chapter 3 3 soils and plant nutrition ... tennessee master gardener handbook 53 oflcal tmg...

Chapter 3Soils and Plant

Nutrition

Learning Objectives1. Name the main components of a soil

2. Explain the origin and functions of inorganic and organic matter in a productive soil

3. Describe soil productivity factors and the importance of soil fertility

4. Describe several methods to improve soil texture

5. Explain soil fertility and its relationship to the plant

6. Explain the factors that influence soil fertility and plant nutrition

7. Explain the benefits of using compost in gardens

8. Explain how to recognize and prevent common problems with composting

9. Explain the factors that affect the composting process

Tennessee Master Gardener Handbook 52

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Soil is the medium to support plant growth and development. Within recorded his-tory, the soil systems of the world have

played an essential role in the production of food and fiber. These systems may play an increasingly important role in the production of crops as renewable sources of energy.

Improving and sustaining soil systems are widely studied topics. Soil productivity refers to the capacity of the soil to produce plants. Some soil productivity factors are soil land-scape position, slope, rooting depth, drainage, texture, organic matter, structure, presence of rock fragments, available water-holding capacity and fertility. Soil fertility refers to the quality of a soil that enables it to supply a plant with essential nutrients in adequate amounts and proportions. It is especially important be-cause it is easily adjusted, relative to the other soil factors affecting the soil system.

Soil FormationParent material is the basis of soil. It is made up of bedrock and unconsolidated deposits. Parent material is one of the constituents that plays a role in the formation of soils, also in-cluded is time, topography, climate, plants and animals forms and develops the soils of Ten-nessee. Although soil boundaries are not clear, some general statements can be made about the physical and chemical properties of a soil based upon knowledge of the parent material from which it developed. There are nine parent material regions of soil in Tennessee. Soils in each of these regions have some physical and chemical properties due to the type of parent materials in which they developed. Many of these properties such as soil texture, rooting depth cannot be feasibly changed except per-haps for very small unit areas. Each of the nine regions is discussed in detail below.

Soils and Plant Nutrition

Figure 1. Physiographic Regions and Soil Parent Materials of Tennessee


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Region One: ▪ The Mississippi River flood plains ▪ Soils derived from stream-depos-

ited sediments called alluvium ▪ Soils are generally fertile and range

from fine-textured, firm and slowly-drained, to loamy and well-drained

▪ Alluvial soils may be found along the major stream bot-toms in all regions of the state

Region Two: ▪ Deep loess ▪ Soils derived from a moderately deep

to deep layers (4 to 70-feet) of silt material deposited by the wind (called loess) over coastal plain (materials of marine or oceanic origin) sands

▪ Soils are characterized by fra-gipans (hard layers)

▪ Fragipans restrict drainage, lower avail-able water-holding capacity and are impervious to penetration by roots. They may limit yield potential when found at shallow depths (< 25 to 30-inches) and the erosion of overlying materials can re-sult in a tremendous loss of productivity

Region Three: ▪ Coastal plains and shallow loess ▪ Soils derived from marine deposits of

unconsolidated gravel, sands and clay ▪ Sloped areas have soils that are vari-

able in texture and low in fertility ▪ Smooth areas have soils that have

silty topsoils and variable sub-soils, depending on the nature of the underlying marine deposits

Region Four: ▪ Highland Rim ▪ Divided into the eastern and western sections ▪ Soils primarily derived from lime-

stone-containing chert (a min-eral high in silica and very resistant to degradation) or shaly limestone

▪ Level portions of the rim have silty deposits (loess), some with fragipans

▪ Ridge slopes and the escarpment above the central basin have cherty soils

▪ These soils are low in fertil-ity and have restricted drainage

▪ A large portion of the eastern Highland Rim is referred to as "The Barrens"

Region Five: ▪ The Central Basin ▪ Soils in the hilly portion of the Outer

Basin, below the Highland Rim, derived from cherty limestones. Topogra-phy in this area consists of strongly-sloping, narrow and irregular ridges

▪ Soils in the smoother parts of the Outer Basin derived from phosphatic limestone. In this area, fertility is medium to high

▪ Soils in the Inner Basin derived from level-bedded limestone. Some of the soils here are highly produc-tive, while many are limited be-cause they are shallow or stony

Region Six: ▪ Cumberland Plateau ▪ Soils derived from sandstone and shale ▪ Topography is relatively smooth; how-

ever, streams have dissected some areas and formed steep-rocky slopes

▪ Soils are shallow and low in fertility

Region Seven: ▪ The Sequatchie Valley ▪ Similar in parent materi-

als and soils to Region 8

Region Eight: ▪ Ridge and Valley or Great Valley ▪ Soils derived primarily from lime-

stone with narrow belts of soils de-veloped from shale and sandstone

▪ Topography is strongly-rolling to hilly ▪ Internal drainage is moder-

ately- to well-drained ▪ Soils developed in high-grade

limestone and cherty limestone have depths of 8 to 20-feet

▪ Soils developed in shale are often shallow

Region Nine: ▪ West slope of the Appalachian

mountains or Unaka Range ▪ Topography is steep and stony with soil

that is shallow, acidic and low in fertility ▪ Parent rocks are chiefly quartz-

ite and slate with smaller amounts of gneiss, schist and granite


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Soil CompositionMany soils are arranged in three distinct layers or horizons (Figure 2). Each layer may have two or more distinct sub-layers. The principal horizons (collectively called the soil profile) are: A, the surface soil, B, the subsoil and C, the material that has only been slightly affected by soil-forming processes. Soil in the C-horizon may or may not be like the parent material and excludes bedrock such as granite, sandstone or limestone. A sub-layer is defined for cultivated soils; it is often called the Ap ho-rizon, or the plow layer. This zone is distinctly altered by cultivation. The plow layer often includes the A-horizon and some part of the B-horizon. In landscapes with severe erosion or construction disturbance, the plow layer may be mostly the B-horizon.

A desirable soil for plant growth contains about 50 percent by volume solid material and 50 percent open or pore space. The physical composition (Figure 3), consists of 0.1 percent living organisms, 1 percent decaying remains of plants and animals, 48.9 percent weathered rock fragments (gravel, sand, silt, clay) and 50 percent air and water. Each of these compo-nents affects water and nutrient availability to plants and soil productivity.

Living OrganismsLiving organisms play important roles in nutrient cycling, nutrient availability, soil structure development, soil permeability and plant disease. For example, animals such as earthworms, beetle grubs or ants may bur-row into the soil increasing its permeability to air and water. Microscopic organisms such as bacteria, fungi, actinomycetes and animals (protozoa, nematodes) may play important roles in decomposition and nutrient cycling. Some specific types of bacteria (Rhizobium), in association with leguminous plants such as clovers or beans, can play an important role in capturing atmospheric nitrogen that is later used by plants for growth and development. The role of nitrogen in the soil and in the en-vironment is further explained in the Tip Box entitled Nitrogen in a Nutshell.

Figure 2. Soil Horizons

Figure 3. Components of a Desirable Soil

Figure 4. Mycorrhizal fungi under magnification


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Organic MatterCultivated soils in Tennessee usually have less then 1 percent, by weight, of organic matter. The organic fraction of the soil includes plant and animal residues, cells and tissues of soil organisms and substances synthesized and secreted by soil organisms. The very fine and more or less stable fractions of organic matter

remaining after plant and animal residues have been decomposed by the action of organisms living within or in association with the soil are called humus. Organic matter is beneficial to the soil in the following ways:

▪ Decreases erosion ▪ Improves the physical condi-

tion, the tilth, of the soil by en-hancing soil structure

▪ Supplies plant nutrients ▪ Increases the soil’s abil-

ity to hold nutrients ▪ Increases water-holding ca-

pacity of the soil ▪ Serves as a buffering agent

Organic matter, such as compost or crop residues, decreases the amount of available water in sandy soils by cementing the par-ticles together, which reduces the volume of the large pore. In fine textured soils, adding organic matter encourages aggregation, which increases the number of pores small enough for water to be available for plants.

Adding organic matter to medium textured soils does not have a dramatic effect on avail-able water in the soil. However, organic matter can contribute vital nutrients to soils. In the South, organic matter breaks down quickly due to the humidity and heat, which increases microbial activity.

Water, Air and Mineral MatterWater enters the soil through cracks, holes and openings between soil particles. Large openings, such as those made by large roots or earthworms, are called macropores. The small-er openings are called micropores. As water enters the soil pores, air is pushed out and the water becomes known as the soil solution. The soil solution contains dissolved nutrients and other chemicals. It acts as a medium for the movement of plant nutrients and other chemi-cals into the plant. Plant nutrients dissolved in the soil solution are highly available to the plant for uptake and use in growth and devel-opment. As the plant takes up nutrients from the soil solution, the nutrients are replenished by rock and mineral fragments, secondary minerals, organic materials, and undissolved

Mycorrhizal Symbiosis: An Important Component of Healthy Soils

Mycorrhizal fungi usually colonize roots of most native and many crop plants (See Figure 4). Mycorrhizal fungi are beneficial soil microbes that can help plants in a number of ways. Mycorrhizal symbiosis dramatically improves phosphorus nutrition of plants, especially those growing in phosphorus-limited soils. This has been demonstrated for hundreds of plants, both woody and her-baceous. In exchange for enhancing acquisition of phosphorus, as well as some of the immobile micronutrients and possibly nitrogen, the fungus receives vital carbon compounds from the plant to en-able it to live.

Mycorrhizal fungi are also thought to increase plant resilience to other environmental limitations such as drought, salinity, some pollutants, herbicides and infection by pathogenic fungi.

One of the most important agricultural consequences of encour-aging healthy populations of mycorrhizal fungi in soils may be for the soil itself. The fungi’s tiny but prolific hyphae spread out into the soil and exude organic substances, which help promote good soil structure and retard soil erosion. In fact, the fungi are so adept at improving soil structure and allowing plants to survive in harsh conditions, that they have been used in sand dune stabilization, mine reclamation and phytoremediation.

Figure 5. Aggregate StabilityAggregate Stability as Influenced by the Presence of Organic Matter


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nutrients. These things are known as the solid phase of the soil.

The rate of replenishment depends on many factors, including temperature, concentration of nutrients in the solid phase and the nature of the solid phase itself. A soil system that is able to quickly replenish plant nutrients in the soil solution is highly buffered. For more in-

formation on the relationship between soil and water see Chapter 4, Water Management.

Pore space not occupied by the water con-tains air, which is necessary to supply oxygen to the roots of most plants. The soil air usually contains less oxygen and more carbon dioxide than the air above the surface of the soil.

The composition of the mineral portion of the soil is partially dependent upon the type of parent material from which the soil devel-oped. The mineral portion of the soil is made up of a mixture of particles of various sizes and plays a large role in determining soil physical and chemical properties. For example, soils developed from sandstone are characteristically sandy and low in fertility.

Soil Physical PropertiesThe physical properties of a soil are those characteristics that can be seen or felt between the thumb and fingers. Some important soil physical properties are landscape position, slope, rooting depth, color, drainage, texture, structure, presence of rock fragments and available water capacity. These characteristics are the result of soil parent materials being affected over time by climatic factors, such as rainfall and temperature; topography, such as slope, direction or aspect; and kind and amount of life forms, such as forest, grass and animals. A change in any one of these influ-ences usually results in a difference in the type of soil formed. Important physical properties of a soil are color, texture, structure, drainage, depth and surface features, such as stoniness, slope and erosion.

Physical properties and chemical compo-sition largely determine the suitability of a soil for its planned use and the management requirements to keep it most productive. To a limited extent, the fertility of a soil deter-mines its possible uses, and to a larger extent, its yields. However, fertility level alone is not indicative of its productive capacity. This is because soil physical properties usually control the suitability of the soil as growth medium. Fertility is more easily changed than soil physical properties.

Figure 6. Soil Water Content

A.

Saturation is the point when all the pores are filled with water.

B.

Field Capacity is the maximum amount of water that a soil can hold against a gravitational force.

C.

Permanent Wilting Point is the amount of water left in the soil when plants wilt permanently

Mineralization

Organic matter contains about 5 percent nitrogen and 0.5 percent phosphorus and sulfur. The conversion of plant nutrients in or-ganic matter to inorganic forms that are available for use by plants is called mineralization. In tilled systems, about 1 to 2 percent of this organic matter will mineralize each year. For example, it is com-monly estimated that the surface 6-inches of soil in 1 acre (referred to as an acre furrow slice) weighs about 2 million pounds. If that soil contains 1 percent organic matter and 2 percent is decomposed in one year, then 20 pounds of nitrogen and 2 pounds of phosphorus and sulfur will be released to the mineral soil within that year. This release, however, has to be replaced by new additions to organic matter.


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Soil Landscape PositionWhile topography refers to the lay of the land (level, undulating, rolling, steep), landscape or physiographic position relates to the origin and age of the landscape form. The same or differ-ent topographies (upland, terrace, footslope, depression, bottomland) may exist on differ-ent landscape positions. Landscape position is important because it can affect flooding hazard and water supply (Figure 7).

Uplands and terraces are similar landscape positions. Upland soils developed primarily from the underlying rock, marine deposits, loess or other materials not deposited by streams. Terrace soils are developed in materi-als deposited by old stream actions (alluvium). Terraces were previously bottomlands before the stream entrenchment. Soils on uplands and terraces usually have moderate to strong development of the horizons in the profile.

A footslope is the area at the base of a slope where material that has washed or slid downslope accumulates. Footslopes are in con-cave positions on the landscape, meaning that the soil above the footslopes on the landscape is steeper than the slopes below them. Foot-slopes generally have slight to moderate profile development. They often look like floodplain soils, but are usually on more sloping areas and do not usually flood. Footslope soils receive runoff from higher areas on the landscape giving them a higher water-supplying capacity for plants than the surrounding areas. They are often very productive garden sites if not too wet.

A depression refers to an area surrounded on all sides by higher land. It has no natural outlet for surface water flow and is therefore subject to flooding during heavy rains and the accumulation of salts. Frequency and duration

of flooding can vary considerably and could be a problem when locating a garden site. Soils developed in depressions have slight to moder-ate profile development.

Bottomlands or floodplain soils developed in materials deposited by recent stream action (young alluvium). These soils are in the present floodplain or overflow area and are subject to flooding unless protected by dams or levees. Soils in floodplains usually show little develop-ment of the soil profile. If well-drained, these soils can be productive garden sites; however, there is a risk of flooding.

Soil SlopeSoil slope is the change in vertical elevation over a given horizontal distance. It is impor-tant because steeper slopes usually have more runoff and are drier. They are usually subject to greater erosion and may limit the operation of machinery.

Slope is expressed as a percent, which is equal to change in elevation, divided by the horizontal distance, times 100 percent. Slope can be accurately determined using survey instrumentation. For purposes of selecting a garden site, it can be estimated for a specific area using a tape measure and string. Slope classes of soils have been defined as a means of mapping soils and making recommendations about their use. Slope classes vary between regions. They are often referred to by letters: “A” slopes are nearly level, “B” slopes are gently sloping and so forth up to “F” slopes, which are very steep. Slope classes used in Tennessee are shown in Table 1. Generally, slopes of 5 percent or less are strongly preferred for gar-dens. On steeper slopes, conservation practices like mulches, winter cover, grass strips and possibly even bench terracing will be needed.

Figure 7. Landscape Positions


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Soil Rooting DepthRooting depth is the total depth of soil that will allow root penetration and growth. Layers that stop or severely limit root growth include bedrock, continuous hard pans (fragipans), unconsolidated partially weathered parent material, structureless clay and compact layers of chert or gravel. If root growth is confined to cracks several inches apart, the layer is consid-ered unfavorable for roots. Rooting depth can be divided into four classes:

▪ Deep36 inches or more ▪ Moderately Deep20 to 36 inches ▪ Shallow10 to 20 inches ▪ Very Shallowless than 10 inches

Deeper-rooted soils can provide more water to plants. Therefore, plants growing on deeper soils resist drought better and are more lush and healthy. Shallow soils can be used for gardens, but will require irrigation for healthy, productive plants.

ColorWhen soil is examined, color is one of the first things noticed. Color is important, because it gives an indication of soil conditions such as: organic matter content, extent of weathering (age of the soil) and drainage.

Surface soil colors vary from almost white to shades of brown, gray and black. Light colors can indicate low organic matter content as well as the presence of salt. Dark colors can indicate high organic content. Light or pale colors in the surface soil are frequently associated with relatively coarse texture and highly leached conditions. Dark colors result from poor drainage, low annual temperatures

or conditions such as profuse plant growth and low decomposition rates.

In general, subsoil colors indicate the aeration and drainage status of the soil. Red, brown and other brightly colored subsoils indicate free movement of air and water. If these colors persist throughout the subsoil, it indicates favorable aeration. Some soils with mottled (areas of mixed, variable colors) sub-soil, especially where the colors are shades of red and brown, are also well aerated.

Most soils that have gray mottling in the subsoil, or where gray color is predominant, have too much water and too little air during much of the season. The red-to-brown rust color of the subsoil comes from iron coatings under well-aerated conditions. In frequently wet soils with low oxygen levels and fluctuat-ing wet-dry conditions, the iron coatings may be chemically and biologically removed, leav-ing the gray color of background soil minerals.

DrainageA lack of good soil drainage is most commonly due to a high water table, a slowly permeable layer within the soil profile, seepage or some combination of these conditions. Poor drain-age causes delays in land preparation, delays in cultivation, a delay in soil warm-up and suffocation of roots. Excessive drainage causes weak or dead plants because water cannot be held within the soil long enough for plants to use. Soil drainage influences land use, plant selection, and garden management. Wetter soil can be improved by artificial drainage; droughty soils benefit from irrigation. There are five classes of soil drainage. They are de-fined below.

Table 1. Slope Classes Used in Tennessee

Middle and East Tennessee West Tennessee

Slope Class Range (Percent) Slope Class Range (Percent)

Nearly Level (A) 0 to 2 Nearly Level (A) 0 to 2

Gently Sloping (B) 2 to 5 Gently Sloping (B) 2 to 5

Sloping (C) 5 to 12 Sloping (C) 5 to 8

Moderately Steep (D) 12 to 20 Moderately Steep (D) 8 to 12

Steep (E) 20 to 30 Steep (E) 12 to 20

Very Steep (F) 30 or more Very Steep (F) 20 or more


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Soil TextureSoil texture affects the rate of water absorp-tion, water movement in the soil and the amount of water and nutrients the soil can provide. This water- and nutrient-holding capacity is then very important in determining how easily excess nutrients or pesticides might leach into groundwater and how frequently one might expect to have to lime, fertilize or irrigate. Soil texture also affects ease of tillage, erodibility, fertilizer management and root penetration. Soil texture can only be changed at great cost.

Soil texture is determined by the relative amounts of sand, silt and clay. Sand is the larg-est particle determining soil texture and can be seen by the naked eye. It has a high bulk density (mass per unit of volume) with less sur-face area and larger pores per unit volume than similarly structured silt or clay. Sand holds little water or nutrients and is not slick or sticky when wet. It gives the soil a gritty feel.

The medium-size soil particles are called silt. These particles are too small to be seen without a microscope. The bulk density of silt is between sand and clay. Silt holds a moder-ate amount of water and nutrients. Silt has the feel of talcum powder and is moderately sticky when wet. Water and nutrients are held by silt with less force than those held by clay. As a result, a larger portion of the total amount of water and nutrients are available to the plant.

The smallest soil particles are called clay. Clay is the most chemically and physically active part of the mineral (inorganic) portion of the soil. Clay has a lower bulk density than sand or silt, with more surface area and many fine pores per unit volume. As a result, clay can hold a lot of water and nutrients. Some water and nutrients are held so tightly that they either cannot be used by the plant or cannot be used within the time frame needed to sustain growth and development. Clay can act as a binding agent between sand and silt particles in forming soil structural units. Soils that are high in clay are sticky when wet and hard when dry.

Figure 8. Relative Size of Sand, Silt and Clay

Table 2. Drainage Classes of Soil

Soil type Depth of saturation Saturation period Color

Poorly drained Less then foot from the soil surface During at least one season > 50% gray in the top 10-inch

layer

Somewhat poorly drained Within a foot from the soil surface 1-2 months Some gray colors form

Moderately well drained The lower part of the subsoil 1-2 months

Red, brown, or yellowish colors in the top 10-inches; no gray mottles. Gray mottles or mostly gray within 3-feet of the surface

Well drained Not saturated within 3-feet of the surface Minimal

Reddish, brownish or yellowish to a depth or 3-feet or more without gray mottles.

Excessively drained Not saturated within 3-feet of the surface None to minimal No gray mottles within 3-feet

of the surface


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Figure 9. Soil Textural TriangleAssessing Soil Texture

For gardening purposes, rubbing a moist sample of soil between the thumb and finger can make an adequate as-sessment of soil texture. Three groups (Coarse or Sandy, Medium or Loamy, Fine or Clayey) can be defined based on textural class identified by discerning fingers (Table 3). Experience is the key to this art and one becomes better with practice.

To determine soil texture by feel, start by wetting a sample of soil until it has the consistency of putty or modeling clay. Make a ball of the wetted soil about ½- to ¾-inch in diameter. Press the ball be-tween the thumb and finger. Try to make a thin ribbon from it. Then estimate the texture using the guidelines in Table 3.

Table 3. Estimating Soil Textural Groups and Classes—The Discerning Fingers Technique

Textural Group Textural Classes Description

Coarse (Sandy) Sand, loamy sand

Will not form a ribbon. Feels very gritty because soil is mostly sand. Ball is loosely held together and falls apart easily when handled.

Medium (Loamy)

Sandy loam

Will usually not form a ribbon. Feels gritty, but contains considerable silt and clay. Ball will hold together when handled gently, but will break apart easily when pressed.

Silt, Silt loam, Loam

Forms a very short ribbon that breaks easily. Feels smooth like talc in a silt loam, but with slight grittiness in a loam. Ball will compress only slightly before cracking when pressed. Slightly sticky when wet.

Sandy clay, Loam, Clay Loam, Silty clay loam

Will form a short ribbon that breaks easily. Ball will compress somewhat without cracking when pressed. When smoothed with fingernail or knife blade, will not leave a shiny surface. Sticky when wet.

Fine (Clayey) Sandy clay, Silty clay, Clay

Will form ribbon easily and holds together well. Ball of moist soil can be molded into various shapes with little cracking. Will leave shiny surface when smoothed out with knife or fingernail. Very sticky when wet.


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Judging Soil TextureAn accurate assessment of soil texture can be obtained by laboratory analyses. Soil scientists have defined 12 classes of soil texture (Fig-ure 9). Soil texture can be determined from a textural triangle by locating the appropri-ate particle size content (as indicated by a soil physical analysis) on the outer edges and determining the quadrant where these points intersect. For example, a soil having 30 percent sand, 30 percent silt and 40 percent clay would give a clay/clay loam soil.

Soil StructureSoil structure is the arrangement of individual sand, silt and clay particles into clusters or aggregates. These soil clusters, or aggregates, vary in shape, arrangement, size and distinct-ness, and durability. Soil structure is important in determining rooting depth and percolation rates, which is the amount of water in inches/hour that is able to move through a soil. Well-structured soil is easier to work with because it has free air and water movement.

Presence of Rock FragmentsRock fragments are loose pieces of rocks of any kind or shape larger than sand. Rock frag-ments influence water storage, infiltration and runoff. A soil that is 50 percent by volume rock fragments would have roughly one-half the available water-holding capacity of a similar soil without the rocks. Rock fragments inter-fere with tillage.

The amount of rock fragment is measured as a percentage of the total soil rooting volume taken up by rock fragments. A quick and reli-able estimate of rock fragments can be made by taking a quantity of the soil and separating it into two stacks: fragments and fine particles. If, for example, the stack of fragments is one-fourth as large as the stack of fines, then the soil has 25 percent, by volume, of rock frag-ments. Three classes of rock fragments are: none or few, less than 15 percent rock frag-ments; common, 15 to 35 percent rock frag-ments; and many, more than 35 percent rock fragments. Rock fragment content is averaged over the entire rooting depth.

Figure 10. Common Types of Soil Structure in Tennessee

Crumb and Granular

Blocky

Platy

Prismatic

Massive

Crumb and granular: Aggregates are small particles and weakly held together. It may be roughly spherical with many irregular sur-faces. Has the greatest proportion of large openings between soil aggregates. Usually the most desirable for gardening

Blocky: Usually angular or subangular in shape varying in size from 1/16-inch to 1-inch in diameter. Most subsoils in Tennessee have an-gular or subangular blocky structure. This structure may be strong (easily seen, all particles aggregated) or weak.

Other structures not common in Tennessee soils: platy, prismatic, columnar, massive or single grain.


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Available Water-Holding CapacityAvailable water-holding capacity (AWHC) is the amount of water a soil can store and release for use by plants. For selection of a garden site where irrigation is not possible or too costly, this physical property is of major importance. Concerning soil texture, sandy soils have a low AWHC, silt has the highest AWHC and clayey soils have an intermediate AWHC.

Available water-holding capacity is esti-mated using texture, rooting depth and coarse fragment content. The average AWHC of soils with different textures is shown in Table 4 and

is expressed in inches of water available per inch of soil.

Table 5 can be used to evaluate the effects of AWHC in Tennessee gardens.

Changing and Managing Soil Physical PropertiesSince soil physical properties are costly and difficult to change quickly, the selection of a garden site should involve some assessment of these properties. This is especially important if a choice of sites is available. When site avail-ability is limited, knowing the physical proper-ties will provide a guideline for management strategies to maintain and enhance garden productivity. An assessment can be made by assigning points to the various soil physical properties at each potential garden site. This will involve getting much better acquainted

Estimating Available Water-holding Capacity of a Soil

To estimate the available water-holding capacity of a soil:

1. Determine rooting depth. If 36-inches or more, consider the rooting depth to be 36-inches.

2. Within the rooting depth, determine the thickness, in inches, of each layer of the soil having different textures (coarse, medium, fine).

3. Determine the AWHC for each layer by multiplying the thickness of the layer by the AWHC shown in Table 4 (inches/inch) for the texture of the layer.

4. If any of the layers contain 15 percent or more rock fragments, reduce the AWHC for that layer by a percentage equal to the percentage of rock frag-ments because the volume occupied by the fragments will not hold water. If less than 15 percent fragments, make no deductions.

5. Add the available water-holding capacities for each layer within the rooting depth.

Table 4. AWHC of Soil Textural Groups

Texture of Soil Average AWHC (Inches/inch of soil)

Coarse 0.05

Medium 0.20

Fine 0.15

Table 5. Effect of AWHC on Tennessee Gardens

AWHC (inches) Interpretation

Less than 4.0 Low: May be droughty

4.0 to less than 6.0 Medium: Intermediate Water Supply

6.0 or more High: Good Available Water Supply

Figure 11. Available Water in Five Soil Types


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with the soil. One must actually get down into the soil at each potential site. Tools such as a shovel, soil probe and auger will be essen-tial. The site rating highest when score sheets are totaled should have greater potential for

productivity. A sample score sheet is illustrated in Table 6.

Amendments and cultural practices that benefit soil physical properties include adding ditches, tiles or soil conditioners; minimizing erosion by planting on a contour, terracing,

Table 6. Using Soil Physical Properties to Compare Productivity Potential Among Garden Sites

Soil Physical Property (Select one interpretation for each)

Interpretation Points to Assign

Your Potential Garden Sites

A B C D

Landscape position

Upland 4

Terrace 4

Footslope 5

Depression 2

Bottom 5

Soil slope

Nearly level (A) 10

Gently sloping (B) 7

Sloping (C) 3

Moderately steep (D) 1

Steep (E) 0

Very steep (F) 0

Soil rooting depth

Deep 10

Moderately deep 6

Shallow 3

Very shallow 1

Drainage

Poorly drained 1

Somewhat poorly drained 3

Moderately well drained 5

Well drained 5

Excessively drained 2

Surface soil texture (A Horizon)

Coarse 2

Medium 5

Fine 3

Surface soil structure

Granular 5

Crumb 5

Other 2

Presence of rock fragments

None or few 5

Common 3

Many 1

Available water-holding capacity

Low 3

Assign a 10 to all categories when irrigation will be used. 6

High 10

Totals


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maintaining soil cover and minimizing tillage; using green manure; using plant residue; and encouraging healthy earthworm populations. Keep in mind that any modifications made to the soil may show few immediate beneficial ef-fects. The full benefits are usually realized over long periods of time; years instead of weeks or months.

Ditching or TilesSoil drainage can be improved by ditching or by installing tile drains. Ditching provides a place for the water to go. It also lowers a high water table. Ditching alone may result in sub-stantial improvement of drainage, especially with coarse- and medium-textured soils or soils with a well-structured subsoil.

Installing tile drains changes the pore size distribution of a sufficient volume of soil in strategic locations so that movement of water is faster, especially in fine-textured soils with many small pore spaces. Local, state, federal or other appropriate regulations should be adhered to before engaging in any large-scale project to improve drainage. If ditching and tiling are not viable options, an alternative is planting a garden on a raised bed.

Soil ConditionersSoil conditioners are used to improve soil physical properties. Some soil conditioners, such as animal manure, may also significantly affect soil chemical properties. Some common-ly used soil conditioners include sand, com-posted materials, animal wastes, peat, perlite, vermiculite and various potting soil mixtures. Availability and costs associated with haul-ing and spreading the large amounts needed to effect significant changes in soil physical properties are major limitations to the use of soil conditioners. Chemical soil conditioners, such as Gypsum, are often used to reduce high

soil strength caused by the dispersive effects of sodium. However, research has shown no advantage to their use in most situations.

Green Manure Cover CroppingGreen manure cover crops are usually planted in the late summer or early fall and plowed under either in late fall or several weeks before spring vegetable garden planting. They provide large amounts of organic matter, some nutrients and protection from erosion over the winter. They are useful to gardeners trying to improve their soils, especially those who are unable to compost enough material for their large gardens. They may also be used over the growing season in a rotation system designed to control plant pests or improve soils.

There are two types of green manure cover crops: legumes and non-legumes. Legumes can add nutrients to the soil because they have root nodules that contain nitrogen-fixing bacteria. They fix more nitrogen when mixed with a non-legume crop in the garden than when grown alone. It is not unusual for a mixed legume planting to fix 20-300 pounds of nitrogen per acre. Legumes may also have very deep roots, which improve soil drain-age and bring up nutrients from the subsoil to levels where shallow-rooted plants can use them. Peas, beans, clover, vetch and alfalfa are examples of legumes.

The non-legumes used as green manure cover crops are mostly grasses. They are grown because they are economical, easily established and can quickly produce large amounts of organic material. Examples include annual ryegrass, oats, wheat and millet.

Cover crops may be left to decay on the soil surface, chopped or mowed with a rotary lawn mower. This needs to be done before their

Table 7. Green Manure Crops

Cover Crop Sowing Time Time to Turn Under

Crimson clover (Trifloium incarnatum) Fall or spring Fall or spring

Hairy vetch (Vicia villosa) Fall or spring Fall or spring

Buckwheat (Fagopyrum esculentum) Late spring or summer Summer or fall

Oats (Avena sativa) Spring or fall Spring, fall or summer

Rape (Brassica napus) Spring or fall Sumer or fall

Winter rye (Secale cereale) Fall Spring


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seeds mature. Allowing a cover crop to remain on the soil surface will provide about the same amount of nitrogen as turning it under and it may help reduce erosion and retain moisture. It could, however, also provide a place for insects and disease pathogens to overwinter. If cover crops are turned under, be sure to allow at least six weeks for them to decay before planting. This will reduce nitrogen immobilization problems.

Crop ResiduesCrop or plant residue is the portion of the plants remaining after harvest. This residue is a significant source of organic material. It can be left on the surface where it grew, used as mulch, composted or turned under. Leaving plant residues on the surface slows breakdown of the organic material so total soil organic material increases. However, insect, disease and weed problems are increased due to these pests overwintering in the debris. Turning crop residues under cause them to break down faster, which may release nutrients. Addi-tionally, some insects and diseases are less likely to survive if their host plant material is eliminated.

Soil Fertility and Plant NutrientsPlant nutrition should not be confused with fertilization. Nutrition is the plant’s need for basic chemical elements. Fertilization is the application of those elements to the environ-ment around the plant. Plants require 16 nutrient elements to survive and produce seed. Air and water provide carbon, hydrogen and oxygen. The soil usually supplies the remain-ing 13 essential mineral elements: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), chlorine (Cl), copper (Cu), iron (Fe), manga-nese (Mn), molybdenum (Mo) zinc (Zn) and nickel (Ni).

Nitrogen, P and K are classified as primary macronutrients based on the large amounts of each required by plants, see Table 8. Although the movement of N, P and K varies in soils, once inside a plant, all three may be mobilized, moving from one plant part to another.

Calcium, Mg and S are categorized as sec-ondary macronutrients because plants require

less of these three essential elements than N, P and K. Magnesium and S are mobile in plants. However, Ca cannot be transported from old leaves to support new plant growth. This is why calcium deficiency symptoms occur first on new leaves.

In Tennessee, most native soils contain enough of each micronutrient to support healthy plants. The micronutrients are boron, chlorine, copper, iron, manganese, molybde-num and zinc. Micronutrients are just as es-sential as the primary and secondary nutrients; however, deficiencies are rare and can be easily corrected because garden crops need small quantities. See Table 8 for a list of each of the essential nutrients.

For the 13 nutrients to be available to the plant, the plant must first absorb them. Some 98% of these nutrients are absorbed into the soil solution surrounding the plant, while only 2% are absorbed when in direct contact with the root hairs.

Nutrients found in the soil solution are ions. Ions are charged components of individual molecules. The ions most readily absorbed are listed in Table 8. Cations, which are positively charged ions, find sites on the negatively charged soil particles and organic matter. Anions, which are negatively charged ions, are not held by the colloids and are lost through leaching.

Ions enter the soil solution by dissolv-ing from a salt. Some salts, such as potas-sium nitrate (KNO3), dissolve easily and stay in solution, separating into K+ and NO3-. However, not all ions stay in solution. Some combine with other ions and become unavail-able to the plant. This phenomenon is espe-cially pH dependent. So, the NO3- is lost and the K+ remains. Some cations are stronger than others, depending on the amount of the ionic charge on the soil particle. Hydrogen is held the strongest, then calcium, magnesium, potassium and then sodium. Therefore, each soil particle has a total potential charge that dictates its holding capacity; this is the cation exchange capacity (CEC). Clays have the greatest CEC and sand has the least. Organic soils especially retain cations; therefore, add-ing organic matter significantly increases the nutrient availability of a soil. Thus, a plant deficiency may not result from a nutrient being absent rather, the ionic charge may be weak due to an unfavorable pH. This would cause


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there to be no available exchange sites in the soil solution.

Nutrient mobility, or immobility, provides us with special clues when diagnosing defi-ciency symptoms. If the deficiency symptom appears first in the old growth, we know that the deficient nutrient is mobile. On the other hand, if the symptom appears in new growth, the deficient nutrient is immobile. When there is sufficient moisture in the soil for leaching to occur, the percolating water can carry dis-solved nutrients that will be subsequently lost from the soil profile. The nutrients that are easily leached are usually those nutrients that are less strongly held by soil particles.

As stated above, nutrients enter the plant through water-soil solution. This uptake is either passive, meaning no energy is expended, or active, meaning energy from respiration is used to take up water. Passive uptake works within a concentration gradient from sur-rounding salt concentrations. Water moves through the root hairs from a lower concen-tration to a higher concentration. This is how molecules of nutrients are carried into the plant. If passive absorption does not take place, then the plants must rely on active absorption to remain healthy.

Table 8. Essential Mineral Elements Required by Plants

Classification Common Name Scientific Name Amount Needed

Mac

ronu

trie

nts

Primary

Nitrogen N NO3-, NH4

+ Mobile

Phosphorus P H2PO4-, HPO4

2- Mobile

Potassium K K+ Mobile

Secondary

Calcium Ca Ca2+ Immobile

Magnesium Mg Mg2+ Mobile

Sulfur S SO42- Mobile

Mic

ronu

trie

nts

Trace (Minor)

Boron B H2BO-, HBO32-, BO3

3- Immobile

Chlorine Cl Cl- Mobile

Copper Cu Cu2+ Immobile

Iron Fe Fe2+ Immobile

Manganese Mn Mn2+ Immobile

Molybdenum Mo MoO42- Mobile

Zinc Zn Zn2+ Immobile


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Nitrogen in a Nutshell

What is so important about nitrogen?Nitrogen transformations are some of the most important biological changes that occur in the soil. These transfor-

mations have significant effects on soil fertility and nitrogen uptake by plants because nitrogen is usually the most limiting plant nutrient in Tennessee soils. Nitrogen transformation relies on specific soil bacteria and environmental conditions.

What are Nitrogen Sources?Some nitrogen sources are very soluble in water and are released within hours after being applied. Others, known

as controlled-release, are formulated to dissolve or release into the solution surrounding the roots very slowly.

Table 9. Examples of Inorganic and Organic Nitrogen Sources

Inorganic Sources Natural or Organic Sources

Ammonium nitrate, ammonium sulfate, calcium nitrate and potassium nitrate

Dried, activated sewage sludge; animal by-products, such as manure, feather, leather and blood meal; and plant by-products, such as corn gluten meal and proteins

Each is very soluble in water and may absorb moisture from the air during storage. Foliar or root burn can occur in plants if too much is applied.

Nitrogen is usually released slowly as a result of soil microorganisms activity. Have a very low burn potential. During cold temperatures, microorganisms are inactive and N is not released.

The rate of release varies among the synthetic organic nitrogen sources. Urea, one of the most concentrated and widely used quickly available, synthetic organic nitrogen sources, releases nitrogen rapidly and can burn turf when improperly applied. Coated, slow-release nitrogen sources are formed by coating granular urea with molten sulfur, a polymer, or a combination of the two.

How is Nitrogen Transformed?Microorganisms

Before growing plants can use organic material, various microorganisms must convert the organic material into forms the plant can use: ammonium (NH4

+) and nitrate (NO3-) ions. The transformations from organic nitrogen to

plant-available nitrogen occurs in three major steps: aminization, ammonification and nitrification. The chemical reactions of each of these steps are detailed below.

▪ Aminization (proteins to amino acids) ▫ Proteins → bacteria → amino acids (R-NH2) + CO2 + energy

▪ Ammonification (amino acids to ammonia) ▫ R-NH2 + H2O → bacteria → NH3 + R-OH + energy

▪ Nitrification (ammonium to nitrates) ▫ R-NH4

+ + 3O2 → bacteria → 2NO2- + 2H2O + 4H+ + energy

▫ 2NO2- + O2 → bacteria → 2NO3

- + energy

These same transformations occur when fertilizers containing ammonium or nitrate forms of nitrogen are added to the soil. There are also bacteria that convert nitrate nitrogen back to nitrogen gas (N2). These bacteria are most active when soils are waterlogged and no oxygen is present. The bacteria use the oxygen in the nitrate ion for their metabolism. The result is a loss of soil nitrogen back into the atmosphere, and nitrogen deficient plants.


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Environmental ConditionsAll nitrogen transformations and the persistence of ammonium and nitrate in the soils are influenced by other soil

conditions such as soil acidity or pH, air, temperature and moisture. If the soil has a low pH, less than 5.5, most bacteria cannot thrive. Therefore, the rate at which each transformation occurs is reduced considerably. If air is lacking, denitri-fication, the conversion from nitrate (NO3-) to nitrogen gas (N2), occurs and nitrogen is lost to the atmosphere. If there are cool temperatures, little ammonium is changed to nitrate. Since ammonium (NH4+) is a positively charged cation, it is held by the soil’s cation exchange capacity and is not readily leached as nitrate (NO3-), an anion. If temperatures are too warm, the conversion of ammonium to nitrate is sped up. If the soil is warm, moist and well aerated during the growing season, most of the plant-available nitrogen is in the nitrate form. Even fertilizer nitrogen added as am-monium sulfate, ammonium nitrate, urea or anhydrous ammonia is rapidly converted by soil bacteria into the nitrate form in warm, moist soils. Nitrates are subject to leaching. Periods of high rainfall can result in the loss of these ions from the rooting zone. This is why most Tennessee soils are very low in nitrogen, and fertilizer nitrogen, manures or large quantities of compost are necessary to provide the nitrogen needed in the garden.

Nitrogen Fixation by Legumes

Another important microbial transformation is the fixation of atmospheric nitrogen (N2) into plant nitrogen. This is accomplished by bacteria called Rhizobia living in association with the roots of legumes. The atmosphere is about 78 percent nitrogen gas (N2), but higher plants cannot use it. Rhizobia bacteria take the nitrogen from the air and

Figure 12. Transformation of Unusable Nitrogen Forms into Useful Nitrogen Cations


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Soil pHThe pH of soil, or more precisely the pH of the soil solution, is very important because the soil solution carries nutrients such as nitrogen (N), potassium (K) and phosphorus (P) that plants need to grow, thrive and fight off diseases. Soil pH values can range from 1 to 14. Seven is considered neutral, anything above seven is alkaline, or basic, and anything below 7 is acidic. The pH scale is logarithmic, not linear. So a pH of 8.0 is 10 times more alkaline than 7.0, while a pH of 5.0 is 100 times more acidic than a soil with a pH of 7.0. Ornamental plants generally prefer a pH range of 5.2 to

6.5; most vegetable crops prefer a pH of 6.0 to 6.5 (see Figure 14. pH Availability Chart).

Because nutrient availability is determined by the pH of the soil solution, if the soil is too acidic, plants cannot utilize N, P, K, S, Ca, Mg and Mo. As a result, the plants will show signs of deficiencies. Additionally, nutrients like aluminum, iron and manganese become toxic. Plants are also more likely to take up toxic metals and some plants eventually die of toxicity. In contrast, if the soil is highly basic, deficiencies of iron, manganese, boron and molybdenum can occur. Very alkaline soils are low in N, P, Fe and Mn and are often high in

convert it into an amine (R-NH2) form that they and their host plant can use for building amino acids and proteins. Only legumes such as peas, beans, clovers, and vetches can support these nitrogen-fixing bacteria. Some trees are also legumes (mimosa, redbud, locust) and many weeds are legumes (beggarweed, sicklepod, kudzu). When the le-gumes die or are turned under, the nitrogen in the plants is mineralized into the soil where other plants can utilize it.

Most garden soils contain an abundant supply of Rhizobia bacteria. However, on uncultivated land, inoculating legume seed with live Rhizobia bacteria specific for that plant may be good insurance. It certainly costs less than fer-tilizer nitrogen. On the other hand, if legumes are fertilized with nitrogen, the Rhizobia may remain inactive and not fix atmospheric nitrogen. The presence of active Rhizobia on legume roots is apparent by observing the presence or absence of small, round nodules on the roots. Nodules that are actively fixing nitrogen will have a pink color when broken. Table 10 shows how much nitrogen per acre a good crop of legumes can fix.

Table 10. Nitrogen Fixed from the Air by a Good Crop of Legumes

Legume Nitrogen Removed From Air (pounds N per acre)

Alfalfa 200

Soybeans 130

Peanuts 120

Cowpea 86

Clover 80

Vetch 80

Garden beans 60

Other Nitrogen Fixing Organisms

Certain blue-green algae and other organisms are known to fix atmospheric nitrogen. However, the amount of nitrogen fixed by these microorganisms is very small and not even considered important in the home garden. In the past, some products have been offered for sale with the claim that they inoculate the soil with these special mi-croorganisms or stimulate their growth by adding seaweed extract or some other natural, organic material. In most cases, the soil already contains these microorganisms, but the conditions for optimum growth of garden plants do not favor the optimum growth of blue-green algae and other nitrogen-fixing organisms. Adding these products to the soil will not improve conditions any more than good gardening practices.


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soluble salts. Plants in these soils show nutrient deficiencies as well.

The pH level of a soil solution can be determined by a soil test. When the results of the soil test are known, the pH can be adjusted with lime, which will raise the pH and im-

prove soil fertility, and acid forming fertilizers, which will lower the pH. The amount of lim-ing materials needed depends on the type of liming material being used, existing soil pH, soil type (see Table 11) and the unit of change desired to meet the pH requirement of the plants being grown. Liming can improve soil fertility in the following ways:

▪ Add calcium and magnesium ▪ Raise the pH so that Mo, K, P

and S become more available ▪ Reduce the possibility of tox-

icities from Al and Mn ▪ Enhance beneficial microbial activ-

ity for better nitrogen fixation ▪ Improve the soil structure of clay soils

through the aggregating actions of Ca

For most garden and landscape plants, lim-ing materials should be spread uniformly and mixed into the top 6 inches of soil. However, no more than 50 lbs. of limestone should be spread at one time for existing lawns or gar-dens. If the soil test recommends more, the ap-plication should be split and applied 6 months apart. Limestone can be added to lawns any-time of year, and it will be available to plants

Reasons Why a Soil Is Acidic

Soils may become acidic for a number of reasons:

▪ The parent material was acidic ▪ Rainfall leached the soluble calcium ▪ Plant roots excreted hydrogen ions (acid forming) to assist in

nutrient uptake ▪ Plant roots produced carbonic acid to breakdown organic

matter for nutrient release ▪ Plant was exposed to acid rain

Soil Acidification

When ammonium (NH4+) is converted to nitrate (NO3

-), H+ is released into the soils. An increase in the hydrogen ion concentration in the soil results in a low-ering of the soil pH. This is why fertilizers containing ammonium, and most organ-ic nitrogen sources, tend to make the soil more acid.

Figure 13. Development of Acid Conditions in Soils

Table 11. Amount of Limestone Needed to Raise the pH to 6.5

Change in pH DesiredPounds of Limestone per 1000 ft2

Sand Sandy Loam Loam Silt Loam Clay Loam

4.0-6.5 60 115 161 193 230

4.5-6.5 50 96 133 161 193

5.0-6.5 40 78 105 129 152

5.5-6.5 28 60 78 92 106

6.0-6.5 14 32 41 51 55


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until it is in the soil solution. Liming in the fall enhances the movement of limestone into the soil. This is because as the ground freezes and thaws, it increases in porosity. Also, keep in mind that it is not recommended to apply liming materials and soluble nitrogenous fer-tilizers at the same time; it can lead to a rapid release of nitrogen.

In some cases, lowering the soil pH is necessary. This is usually done with a sulfur source, see Table 13. The relationship between soil type and the amount of sulfur that needs to be added is listed in Table 14. It is inadvis-able to add large amounts of aluminum sulfate because the addition can lead to aluminum toxicity in the soils. Also, adding elemental sulfur would not be affective in lowering the pH because the microorganisms would not be active at such a high pH level. Therefore, it is best to use iron sulfate to lower the pH to 6.0, and then use elemental sulfur to reduce the pH further.

Table 12. Common Liming Materials

Materials Chemical Formula CaCO3 Equivalent (100%)Liming Materials (lb) Necessary to Equal 100 lb of Limestone

Burned lime, quick lime CaO (Calcium Oxide) 150 64

Hydrated lime Ca(OH)2 120 82

Dolomitic limestone CaCO3 MgCO3 104 86

Limestone CaCO3 95 100

Marl, marlstone CaCO3 95 100

Shell, oyster, etc. CaCO3 95 100

Using Wood Ashes (Never Use Coal Ashes)

Wood ashes can be used to raise the pH of a soil. Most people find that spreading wood ash is very messy, but it is a way to recycle the ashes properly. It takes about twice as much wood ash as agricultural limestone to raise the pH. However, wood ash is also a good source of potas-sium. If spreading wood ash, spread no more than 10 lbs. of wood ash per 1000 ft2 to avoid toxicity issues. Also, do not allow wood ash to come in direct con-tact with plant roots, young or sensitive plants.

Table 13. Common Acidifying Materials

Materials Chemical Formula CaCO3 Equivalent (100%)Liming Materials (lb) Necessary to Equal 100 lb of Limestone

Soil sulfur S 99.0 100

Sulfuric acid (98%) H2SO4 32.0 306

Sulfur dioxide SO2 50.0 198

Lime sulfur solution CaSx + H2O 24.0 417

Iron sulfate FeSO4 + 7H2O 11.5 896

Aluminum sulfate Al2 (SO4) 14.4 694


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Figure 14. pH and Nutrient Availability Chart

Table 14. Amount of Sulfur Needed to Raise the pH to 6.5

Change in pH DesiredPounds of Sulfur per 1000 ft2

Sand Loam Clay

8.5-6.5 45.9 57.4 68.9

8.0-6.5 27.5 34.4 45.9

7.5-6.5 11.5 18.4 23.0

7.0-6.5 2.3 3.4 6.9

6.0-6.5 14 41 55

Table 15. Amounts of Essential Mineral Elements Commonly Found in Plants and Associated Deficiency Symptoms

Element Effect on Plant Signs of Deficiency/Excess Comments

Nitrogen

Promotes green, leafy growthAids in enzymatic reactions Involved in photosynthesis Helps produce and use carbohydratesPart of plant DNA

Deficiency: Light green or yellowish foliage, stunted growth and shedding of older leaves, yellowing shows first on the oldest leaves. Excess: Excessive vegetative growth, falling over and poor flowering and fruit set.

If not taken up by plants, usually leached away as nitrates (NO3-) or converted to atmospheric N2 gas. Under waterlogged, conditions, N can be converted to ammonia (NH3) gas. Percentage concentration of nitrogen is the first number listed on a fertilizer bag. Nitrogen deficiency can be corrected with fertilizers.

Phosphorus

Essential in energy transformationAssociated with flowers, fruiting, and carbohydrate storage in roots, tubers and bulbs

Deficiency: Difficult to detect in most plants. Results in stunted, darker green plant. Dead areas may develop on the leaves, fruit, and stems. Older leaves affected before younger ones. Purple-ish color seen on some plants. Excess: Inhibits zinc or iron translocation.

Often not practical to correct a deficiency or an excess problem once the plant is growing. Traditional fertilizers formulated for flowering plants are high in phosphorus.Excessive P in surface waters can promote growth of aquatic vegetation.


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Table 15. Amounts of Essential Mineral Elements Commonly Found in Plants and Associated Deficiency Symptoms

Element Effect on Plant Signs of Deficiency/Excess Comments

Potassium

Aids in plant metabolismRegulates the turgidity of cells, respiration and water movementControls stomataIncreases disease resistance Improves winter hardiness

Deficiency: Decline in growth, poorly developed root systems and weak stalks.

Excess: competes with magnesium and calcium for plant uptake and causes “salt” injury.

Soils high in organic matter tend to have higher potassium levels. Excess potassium is not considered an environmental concern.When a deficiency is observed on annuals, potassium fertilization is of little value for the season.

Calcium

Stimulates root and leaf developmentStrengthens plant structure Reduces plant nitrates Stimulates microbial activity, and nutrient uptake Reduces aluminum and manganese toxicity

Deficiency: Poor root growth, black and rotted roots, jelly-like leaf tips.

Excess: Rare

Young leaves and growing points of shoots develop characteristic symptoms of calcium deficiency first. Calcium deficiencies seldom show up when a good liming program is followed and the pH is properly maintained.

Magnesium

Involved in photosynthesisAids in phosphate metabolism and plant respirationInitiates motion several enzyme systems.

Deficiency: Yellow to reddish color appears on the older leaves; leaf veins remain green.

Soils that have been limed with dolomitic limestone (6+% Mg) rarely have magnesium deficient plants. An imbalance between calcium, potassium and magnesium may increase a magnesium deficiency.

Sulfur Essential in protein formation.

Deficiency: Pale green color, appearing first on younger leaves. Deficiencies show up most frequently on very sandy soils in early spring on shallow-rooted plants. Most garden fertilizers contain adequate sulfur.

Contributes to the characteristic odor and taste of garlic, onions and members of the cabbage family. Can leach through sandy soils and can be mineralized from soil organic matter.

BoronImportant in the growing tips of plants, but its exact function remains uncertain.

Deficiency: Stunted plants

Fertilization is recommended for root crops, particularly on sandy soils. Very little boron is needed. Household borax can be used.

Chlorine Stomata regulation Deficiency: Difficult to detect Chlorine is in the soil, most fertilizers, the atmosphere and rainfall

Copper Occurs in several enzymes and certain plant proteins.

Deficiency: No deficiencies observed on mineral soils in Tennessee.

Water flowing through copper pipes get enough to meet a plant’s need.

Iron Maintains chlorophyll in plants

Deficiency: Chlorotic, yellow, tissue between the veins of new leaves. Most common on azaleas, camellias, gardenias, blueberries and centipede turf.

Deficiencies induced by high soil pH, compaction, disease, excessive phosphorus or soil drainage. Foliar fertilization may only temporarily fix a deficiency.

Manganese Activates enzymes

Deficiency: Induced by high soil pH (above 7.0).Excess: Chlorosis and necrotic spots on older leaves, dry leaf tips, stunted roots.

Maintaining the soil pH between 5.5 and 6.5 will avoid toxicity and provide adequate amounts of manganese.

Molybdenum Assimilation of nitrogen in plants Deficiency: Rare, looks like nitrogen deficiency. Liming will usually correct a deficiency.

Zinc Aids in enzymatic reactions. Deficiency: Occurs in new growth, results in smaller leaf size

Deficiencies usually on sandy soils with a pH above 6.5 in early spring or on soils that have recently been limed.


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Soil Testing and Plant AnalysisRoutine soil testing is essential whenever the soil is disturbed, materials are added to the soil or plants are continuously grown in the area. It is important to avoid extremes in pH and fertility levels because this could damage plant health.

Plant analysis is used to diagnose the nutritional status of growing plants. A leaf or a whole plant can be analyzed. This technique is most effective at diagnosing nutritional dis-orders. Your local county extension office may be able to assist if you feel a soil and/or plant analysis is warranted.

Figure 15. Soil Sample

A. From an area of 10 acres or more

B. From a lawn

Figure 16. Soil Sampling Tools and Depth of 6 InchesSoil sampling tools: spade, soil probe, bucket, and depth of 6 inches.

Figure 17. Mixing and Packing the Sample

How to Interpret a Soil Test

For a soil test, each nutrient tested is re-ported in pounds per acre and assigned a soil test category. Nitrogen is not usual-ly reported on a soil test because values for plant available nitrogen are not sta-ble for enough time to give an accurate reading. The ratings for phosphorus and potassium are low (L), medium (M), high (H) or very high (VH). When the second-ary and micronutrients tested are rated as either sufficient (S) or deficient (D).

Recommendations for field crops are reported in pounds of plant nutrients and tons of agricultural limestone to ap-ply per acre. For lawns and gardens, rec-ommendations are reported in pounds of actual fertilizer grades and agricul-tural limestone to apply per 1,000 square feet. Recommendations for vegetables, fruits, flowers and shrubs are reported in pounds per 10 and pounds per 100 square feet.


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Understanding FertilizersFertilizers are added to the plant or soil to provide essential nutrients for optimal plant growth. Nutrients not used by the plant can be lost to the air, surface water or ground water. It is important that gardeners use their soil test or plant indicators to determine the neces-sity of applying supplemental nutrition from a fertilizer. Overuse of fertilizer nutrients can be expensive and detrimental to the environment.

Gardeners often divide fertilizers into chemical or organic categories. Both have similar effects on plant nutrition. The primary differences are the concentration and the relative availability. Chemical fertilizers are made through industrial processes or mined from deposits in the earth and purified, mixed, blended and altered for ease of handling and application. Generally, chemical fertilizers are readily available to plants because soil reac-tions rapidly convert them to the ionic forms that plants take up. Organic fertilizers can be anything from animal manures to composts. Derived directly from animal or plant prod-ucts, organic fertilizer nutrients are generally less available because soil microorganisms must first mineralize the nutrients and then release them in the inorganic, or ionic, form. This can be an advantage where leaching of nutrients is likely but a disadvantage where rapid availability is needed. Organic fertilizers generally contain less total plant nutrients, but have the added benefits of increasing organic matter in the soil.

Fertilizer is rated according to the percent-ages of macronutrients it contains: nitrogen, phosphorus and potassium. 10-10-10 means that there is a balanced rating of 10% nitrogen, 10% phosphorus and 10% potassium.

How to Submit a Soil Sample1. With a spade, trowel, auger or soil sampling tube, take a thin

vertical slice or a core of soil from at least 1020 different places in the area to be tested. Mix all samples thoroughly together in a clean, with no fertilizer or lime residue, container and fill soil sample bag to the FILL LINE, approximately 1 cup. Fold top several times and fasten metal flap securely to avoid spillage during shipment.

2. For row crops sample to plow depth. For example:

▪ Lawns and turf and pasture 4” depth ▪ Gardens 6” depth ▪ Orchards 8”12” depth ▪ Pecan groves 6”8” depth

3. One sample should represent no more than 15 acres. If more than one soil type is present within a sampling area, take a separate sample from each soil type. Avoid sampling high and low spots, areas along roads, old fencerows or fertilizer bands. Sample problem areas separately.

4. Use a waterproof marker to record information on sample bags. Lead pencils and some inks fade during shipment.

5. Samples should not be submitted in plastic bags. This could possibly effect pH and delay the analysis.

6. A routine test consists of pH (lime requirement), phosphorus, potassium, calcium, magnesium, zinc and manganese.

7. Use soil and check submission forms provided by the soil test lab. Send top 2 copies of each form.

8. Refer to Fee Schedule for all special tests and greenhouse/nurs-ery tests.

9. If any additional information is required, either refer to the in-formational packet of material provided by soil lab at secretarial trainings or call the soil test lab at (706)5425350.

10. Soil samples should be submitted to your county Extension office with a Soil Testing information sheet (F394). Soil samples should be sent to specific locations for specific tests:

▪ Soil Test Lab: Lime and fertilizer recommendations ▪ Four Towers: Nematode assay ▪ Riverbend: Pesticide and herbicide analysis

Phosphorus in the Garden

Rose fertilizers are always high in phosphorus. So are African violet fertilizers. Gardeners are sometimes advised to add bone meal (0-10-0) or superphos-phate (0-45-0) when planting lilies, daffodils, tulips, and hyacinths. High phos-phorus fertilizers are fine for container-grown plants, but excessive phosphorus in the landscape has been implicated in surface water pollution problems.


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Types of FertilizerThe following terms may be encountered when dealing with commercial fertilizers that gener-ally fit the chemical fertilizer group.

Fertilizer materialsFertilizer materials are chemical compounds or mixtures containing at least one plant nutri-ent. They can be mixed with other materi-als to form a mixed fertilizer or used alone. Examples are ammonium nitrate, concentrated superphosphate, muriate of potash, gypsum and nitrate of soda.

Dry, blended (mixed) fertilizerDry, blended fertilizers are commercially sold and contain a physical mixture of two or more materials and two or more primary nutrients. They may contain other nutrients as well. Each particle of material can be identified in the blended fertilizer by its color or shape. Blended fertilizer may contain inert filler, such as ground limestone or rock, to make the grade come out even. Examples of popular blended fertilizers sold in bags are: 10-10-10, 13-13-13, 8-24-24 and 15-0-15. Fertilizers can be blended to almost any grade desired.

Dry, granular (homogenous) fertilizer

Heating and adding ammonia to certain materials form dry, granular fertilizers. This causes uniform prills or granules to form. Each granule contains all the plant nutrients listed on the label so the fertilizer is homogenous for an even distribution of plant nutrients. Dry granular fertilizers may be available in some of the same grades as dry blended fertilizers. Dry granular fertilizers are generally complete fertilizers containing some nitrogen, phospho-rus and potassium. Micronutrients may also be included in these because they can be more uniformly distributed in the fertilizer. Most premium or super fertilizers are granular.

Dry, water-soluble fertilizersDry, water-soluble fertilizers are dry materi-als that have been highly purified and blended with no fillers. The products are crystal-lized rather than prilled or granulated so the compounds dissolve more rapidly in water. Sometimes, a soluble dye is added to make the fertilizer easier to see in solution. Water-solu-

ble fertilizers are usually added when watering plants or added through an irrigation system. Because they are highly purified, they usually cost more than granular or blended fertilizers. Examples are some of the specialty fertilizer products sold under the Miracle Growâ or Petersâ brand.

Weed and feed fertilizersWeed and feed fertilizers may be blended or granular fertilizers that contain herbicides preventing certain weed seed from germinat-ing. These must be used strictly as directed on the label or plant injury can result.

Liquid fertilizersLiquid fertilizers are fertilizers that are already dissolved in water. These may contain a lower percentage of plant nutrients than dry fertiliz-ers and are often more expensive, but they are convenient to use in small areas and for foliar fertilization. High-analysis liquid fertilizers are also available to farmers. Another term, “fluid” fertilizers, is used to include liquids and fertilizers suspended in a solution.

Fertilizer spikesFertilizer spikes are “cakes” of fertilizer that are designed to be forced into the soil or into pots. They are easy to use around individual plants but do not provide uniform fertilizer distribution. Nutrients are concentrated near the spike.

Slow-release or timed-release fertilizers

Some dry fertilizers are formulated to release nitrogen slowly into the soil during the grow-ing season. Fertilizer granules may be coated with a resin (Osmocoteâ), sulfur (sulfur coated urea) or a plastic polymer (polymer coated urea) to reduce their solubility.

Organic nitrogen materials are slowly bro-ken down in the soil making them slow-release nitrogen sources (urea formaldehyde). Slow-release fertilizers are excellent for turf, shrubs, fruits and other plants that would normally need several fertilizer applications during the season. They are not suitable for short-season annuals in the home garden.


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Complete fertilizersA complete fertilizer is one that contains all three of the primary plant nutrients, nitro-gen, phosphorus and potassium. It may or may not contain secondary nutrients and micronutrients.

Starter fertilizersStarter fertilizers are small amounts of fertil-izers, containing at least nitrogen and phos-phorus that provide readily available nutrients for new plants and in the early spring when plants are emerging in cool soils. Generally, no more than 1/3 of the recommended fertilizer is applied as a starter fertilizer.

Fertilizer gradeAll fertilizers sold are identified by grade. The grade appears on the label as three numbers, such as 13-13-13, indicating percent nitrogen, phosphate and potash, respectively. Phos-phorus and potassium are listed as phosphate (P2O5) and potash (K2O) because of tradi-tion. At one time all fertilizer nutrients were expressed in terms of the oxide. The actual compounds P2O5 and K2O, phosphorus pent-oxide and potassium oxide, do not really exit. The fertilizer industry has referred to these as “phosphate” and “potash” for so long that its usage and the terms have become a part of the fertilizer industry. Although it can be confus-ing, change is unlikely. If necessary, the fol-lowing factors can be used to convert, but most users think in terms of nitrogen, phosphate and potash and do not worry about the actual amounts of phosphorus and potassium.

P = P2O5 x 0.44 P2O5 = P x 2.29K = K2O x 0.83 K2O = K x 1.20

Choosing a FertilizerTruth Behind the MarketingMany fertilizers sold for homeowners are labeled so the buyer believes they are specifi-cally formulated for a particular plant. This is a marketing tool more than anything else. Fertilizers, or fertilizer materials, should be selected based on soil test results and the plants to be grown. You can save your clients a lot of time and money if you use the following guidelines.

▪ Generally, a higher percentage of N and lower P2O5 is found in fertil-izers labeled for leafy vegetables and

grasses (including corn), because more vegetative growth is desired. This is promoted by the higher nitrogen.

▪ Flowers, bulbs, potatoes, tomatoes and other heavily fruiting plants need less nitrogen because excessive vegetative growth will delay fruiting. Therefore, fertilizers labeled for these plants gener-ally have higher phosphate content.

▪ Fertilizers for acid-loving plants such as azaleas, camellias and blueber-ries are made using ammonium, usually ammonium sulfate, forms of nitrogen because of ammo-nium's effect on soil acidification.

A growing problem in gardens is when a homeowner buys a complete fertilizer, such as 13-13-13 because it is convenient, easily avail-able and relatively inexpensive. However, if the soil test indicates that phosphorus is already very high in the soil, then a fertilizer high in phosphate (P2O5) is not needed, may be detrimental, and is a definite waste, regardless of the plant. Additionally, phosphorus builds up in many Tennessee soils, whereas nitrogen and potassium are often lost through leaching. Therefore, with continued use of a complete fertilizer, phosphorus accumulates to very high and extremely high levels in many garden soils. This causes the plants to weaken and often times, to die.

The Sensible SolutionWhat alternative does a gardener have if the grade needed cannot be found? Fortunately, fertilizer dealers usually carry fertilizer bags with just one or two of the primary nutrients. Materials such as ammonium nitrate (34-0-0), ammonium sulfate (21-0-0-24S), sodium nitrate (16-0-0), concentrated superphosphate (0-45-0), diammonium phosphate (18-46-0), muriate of potash (0-0-60), and potassium ni-trate (13-0-44) can be used instead of complete fertilizers. Per pound of nutrient, the materials may be less expensive than blended or granular fertilizers, and the gardener is not paying for unnecessary products. Secondary and micro-nutrients are also available in small quantities such as gypsum (for Ca and S); zinc sulfate (for Zn); fertilizer borate, or household borax (for B); Epsom salts, MgSO4, (for Mg and S); iron sulfate (for Fe and S); and several forms of chelated micronutrients.


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Fertilizer ApplicationTerms commonly used to describe how fertil-izers are applied include broadcast, sidedress, topdress, banding and foliar fertilization. Each is described in more detail below.

BroadcastBroadcast describes spreading fertilizer evenly over the soil surface. Fertilizers are frequently broadcast prior to planting and incorporated into the soil with normal soil tillage practices. Some nitrogen, most of the phosphorus and potassium, secondary and micronutrients are broadcast to a garden.

SidedressSidedress describes applying fertilizer to one or both sides of growing plants or beside a row of plants. Crops are sidedressed after they are established and growing well. Nitrogen is usually applied as a sidedress because it leaches rapidly through a soil and because plants need additional nitrogen once it is actively growing.

TopdressTopdress describes a uniform (broadcast) application of fertilizer, usually nitrogen, dis-tributed over the top of solid planted crops. For example, a solid bed of turnip greens would be topdressed with nitrogen because sidedressing would be difficult. Turf would be topdressed with nitrogen during the summer.

BandingBanding describes putting all the phosphate, and occasionally some nitrogen and potas-sium, in a band 2-inches below and 3-inches to the side of a row of seeds at planting. The intent of banding is to provide readily avail-able phosphate in soils that test low or very low in available phosphorus. Soils testing low in phosphorus can tie up fertilizer phosphorus if it is broadcast and mixed with the soil. Phos-phate sources are generally lower in salts and not as likely to burn seedlings as nitrogen and potassium fertilizer sources.

Foliar fertilizationFoliar fertilization provides small quantities of plant nutrients to growing plants by spraying a dilute solution of fertilizer on plant leaves This technique is most effective for correcting micronutrient deficiencies (Fe, Mn, B, Mo or Zn) in growing plants. Foliar fertilization is not effective with the primary and secondary nutrients simply because plants cannot take up enough through the leaves. Foliar fertilization will not compensate for poor soil fertility.

CompostingEvery year across America, gardeners till and fertilize the soil; plant seeds, plants, bulbs, shrubs and trees; and, as time goes on, weed, rototil, hoe and water the garden. If these normal gardening habits are followed without considering the improvement of the soil, there will be a:

▪ Loss of available topsoil due to erosion

Table 16. Popular Fertilizer Grades and Materials Available in Tennessee

Fertilizer Grades Percentage of All Grades /Materials Sold in Tennessee

13-13-13 49%

8-24-2 47%

8- 8- 8 7%

5-10-15 7%

7-21-21 7%

5-15-30 6%

18-46- 0 (DAP) 5%

0-20-20 4%

3- 9-18 4%

10-10-10 2%

15- 0-15 <1%

Fertilizer Materials

Ammonium nitrate, NH4NO3 (34-0-0) 45%

Nitrogen solutions, (urea + am. nitrate + water) 26%

Muriate of potash, KCl (0-0-60) 12%

Urea, CO(NH2)2 (46-0-0) 5%

Anhydrous ammonium, NH3 (82-0-0) 4%

Sodium nitrate, NaNO3 (16-0-0) 1%

Ammonium sulfate, (NH4)2SO4 (21-0-0-24S) <1%


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▪ Loss of soil friability due to the re-duction in organic matter

▪ Acidification of the soil due the use of ammonium nitrate fertilizer

▪ Formation of "hardpan" below the sur-face due to repeated use of a rototiller

▪ Extermination of earthworms in the soil due to the use of a roto-tiller and synthetic fertilizers

▪ Gradual loss of trace minerals and therefore gradual loss of soil fertility

▪ Yearly increase in the popula-tion and variety of weeds

However, if the gardener adds compost and uses it regularly, the garden will replenish and maintain soil quality. The items required to successfully create compost include organic

(usually plant) material, a place to pile the material up, water, a little bit of knowledge and time. Composting is not a novel idea; the Indian and Chinese cultures have used composting techniques for thousands of years. Additionally, the ancient Aztec and Mayan cultures were based on a crop system that used composted water hyacinth and water lilies in a raised bed system.

Why Compost?Compost is a mixture of organic residues that have been piled up, watered and partially de-composed. It is a dark, easily crumbled collec-tion of plant and animal products with many of the characteristics of humus-the relatively stable organic component of soils. Composting organic materials at home is a safe and eco-nomical means of disposal and is an effective means of conserving landfill space. Compost benefits the soil and the plants in many ways, compost:

▪ Improves the structure and fer-tility of garden soil

▪ Minimizes fluctuations in soil temperature

▪ Controls weed growth ▪ Protects soil from erosion ▪ Improves clay soil drainage ▪ Allows sandy soil to hold more water ▪ Adds nutrients to the soil ▪ Provides a source of good bacteria ▪ Prevents plant diseases

The Composting ProcessComposting begins when “raw” organic wastes become available to naturally occurring organisms including: bacteria, fungi, thermo-phyllic organisms, actinomycetes, protozoa, earthworms, insects, mites, snails and sow bugs. Composting can happen in a purchased tumbler, can, bin, trench or in a pile on top of the ground. Composting requires time. The amount of time required depends on the mass of the pile, the atmospheric temperature, the moisture content of the pile, the particle size of the organic material, the time frame for adding of additional materials and how often the pile is disturbed. It should be understood that gardening, and especially composting, are

Figure 18.Compost replaces organic matter improving gardening soils

Figure 19. Community Composting


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not for people who demand instant gratifica-tion. Gardens grow at a pace set by genetic and environmental factors and organisms that are turning organic material into compost will consume at a pace also determined by genetic and environmental factors.

Composting BasicsA successful home compost pile depends upon four things:

▪ Mixture of green and brown ingredients ▪ Aeration ▪ Moisture ▪ Container for composting materials

Green Vs. Brown: Carbon Nitrogen RatioOrganic wastes supply organisms (decompos-ers) in the compost pile with carbon (C) and nitrogen (N). Carbon supplies the microorgan-isms with energy and they get this from what is considered brown materials. The microor-ganisms also need protein in order to break down the carbon, which they get from the ingredients green materials. The ratio of C:N

within an organic waste influences the rate at which it decomposes. The goal in composting is to have organic materials in a compost pile mixed to maintain a C:N ratio of 30:1. If the idealized ratio cannot be met, the individual should continue with whatever raw materials are readily available since that is exactly what occurs naturally. When the greens and browns are mixed together they make heat, which makes your compost rot faster.

Greens provide nitrogen: ▪ Grass clippings ▪ Shrubbery clippings ▪ Fresh plant stems/leaves ▪ Newly removed weeds ▪ Kitchen vegetable/fruit scraps ▪ Manures from any herbivore

Browns provide carbon: ▪ Dry leaves ▪ Small sticks or twigs ▪ Cornstalks/corncobs ▪ Straw ▪ Sawdust and wood chips ▪ Shredded newspaper/paper (re-

cycling is still a more environ-mentally friendly option)

Both brown and green materials should be cut or chopped into small pieces to increase the efficiency of the decomposition process. Chipping, shredding or cutting large pieces of organic material will expose more surface area to the decomposers and speed the composting process. This is usually necessary to allow pen-etration of water into the pile. These actions increase the surface area of the organic materi-als but, more importantly, reduce the ability of the materials to form layers that will shed any rainwater.

If an organic residue with a C:N ratio greater than 10:1 is added to the soil, the microorganisms must get extra nitrogen from somewhere else. Otherwise, they cannot break down the organic materials into humus. Ap-plication of a nitrogen fertilizer is an excellent way to speed up the decomposition of residues with a high C:N ratio.

Soil microorganisms are so numerous and effective at using soil nitrogen that they tie it

Speed Up Decomposition?

You cannot speed up the decomposi-tion rate by mixing a bucket of com-posted material with an equal bucket of uncomposted material. The resulting mixture is not half way composted. In most instances the resulting mixture is equivalent to uncomposted material.

Tools Used for Composting

▪ Compost fork or other gardening fork to turn your compost pile

▪ Wheelbarrow to haul compost to and from your pile

▪ Pruners or loppers to trim branches to put on your pile

▪ Compost thermometer ▪ Aerator to get more air into the pile


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up, when supply is low, before higher plants can absorb it. Because decomposing plant resi-due may create a temporary nitrogen deficiency in plants, organic residues should be incorpo-rated well in advance of planting. Once the residue is broken down, the microorganisms start to die and release nitrogen back into the soil for plant use.

TemperatureThe temperature of the pile is a function of: pile size, particle size, C:N ratio, moisture content, pile age, atmospheric temperature and whether the pile is aerobic, anaerobic or aquatic. The observed temperature of an undis-turbed pile can be divided into three distinct steps: initial phase, thermophyllic phase and final phase.

Initial PhaseIn the initial Phase the temperature of the compost pile rises to about 104 degrees F. The initial phase lasts about two to three days.

Thermophyllic PhaseIn the thermophyllic phase, the temperature rises to about 170 degrees F. Most decom-position takes place during this phase. Most decomposers that require oxygen (aerobic) die as the temperature exceeds 140 degrees F. Most seeds die as the temperature exceeds 160 degrees F. As the temperature continues to rise and energy sources are exhausted, the popula-

tion of thermophyllic organisms diminishes. This phase lasts for two months.

Final PhaseDuring the final phase, the temperature stabi-lizes and microorganisms return to live in the compost. This phase will last until the pile is disturbed.

Hot PileIf adding anything to the compost pile that may contain weed seeds or disease pathogens, the C:N ratio is more important so that the compost pile gets hot enough to kill them. Most disease pathogens will die after only 15 minutes or so at temperatures around 130 degrees F. Changing the carbon to nitrogen ratio to 20:1 ensures that the pile will not harvest anything detrimental to the compost. To best monitor the composting process, a compost thermometer with a long probe may be purchased to check the temperature from time to time. Compost temperature tends to spike at around 150 degrees F and then starts to drop. When the temperature drops to around 100 degrees F, it is a good time to turn the compost. When the temperature is no longer fluctuating, the compost is ready. If a gardener is in a hurry to produce compost to add to a garden, the pile can be turned before the temperature reaches 131 degrees F. This will require turning the pile more often, but since the pile will be sustaining optimum tem-peratures longer, the pile will produce compost faster.

Non-Compostable Organic Wastes

Not all organic wastes are suitable for home compost-ing. The following are not recommended:

▪ Manure from any carnivore or omnivore. It may contain harmful pathogens and protein contained therein may produce a noticeable odor upon decay

▪ Fats and oils because they will turn rancid ▪ Meat, dairy or meat byproducts because they may

attract scavengers ▪ Black walnut or Rhododendron scraps/leaves

because they contain natural herbicides that may kill your plants

▪ Tree parts that are larger than a twig because they may take years for them to decompose

Table 17. Average C:N Ratios of Some Organic Materials

Alfalfa 12:1

Clovers 20:1

Animal manures 12-25:1

Sewage sludge 12:1

Corn stalks 40:1

Wheat, rye, oat straw 80-128:1

Sawdust 400-700:1

Grass clippings 20-30:1

Freshly fallen leaves 40-80:1


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Cold PileIf a gardener does not want to take the tem-perature of the compost pile, having “cold compost” is a good option. Even though the pile does not reach the optimum tempera-ture, the compost still rots, just more slowly. Many homes will not produce enough yard and kitchen waste to make a pile that is large enough to reach the optimum temperature for a hot pile. Additionally, it is difficult to create the exact C:N ratio for a hot pile. It is easier to just let the compost pile be and let it rot without worrying about turning it or taking its vital signs. Keep in mind, however, that this method is slower than a hot compost pile. It may take six months or so to get the first load of finished compost. Also, be aware that seeds and pathogens will not die in the cold com-post. Therefore, it is important to keep weed seeds and diseased plants out of the mixture.

AerationAdding air to the compost pile provides the aerobic microorganisms the oxygen that they need. Because aerobic bacteria increase de-composition by as much as 90 percent, adding air to the pile on a frequent basis is essential. To add air to the pile, a gardener can: turn it every two to three days, add a layer of sticks for every 6-inches of green material, build the pile around a PVC pipe with holes drilled in it, poke holes in the compost pile and add wet kitchen garbage (coffee grounds work espe-cially well), or poke and stir the pile.

Turning a compost pile accomplishes several things at once it: adds air to the pile, mixes moist materials with materials that have dried out and mixes less decomposed materials with more decomposed materials.

MoistureFor a compost pile to be successful it should be between 40 and 60 percent water; when touched, it should feel damp. Insufficient amounts of water will cause microbial action to cease. Excess amounts of water will cause a “soggy pile” to form. When this happens, the pile is said to have “soured.”

Compost Pile or Bin SuggestionsFor optimum decomposition, the compost pile/bin should be a minimum size of 3 feet, by 3 feet, by 3 feet. The maximum size parameter is that at least one of the dimensions should not exceed 5 feet. If the pile is too small, it will not get hot enough to allow destruction of the weed seed. If the pile is too big one of two things may happen: Under aerobic condi-tions the pile will tend towards spontaneous

Alternative Aerators

Various types of aerating tools can be purchased. Some interesting, and cheap-er, alternatives that can be purchased at a thrift store include:

▪ Golf clubs ▪ Ski poles ▪ A pair of crutches

Figure 20. Compost Bins

A.

Compost bins made of non-pressure treated wood

B.

Various plastic compost bins


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combustion; under anaerobic conditions the pile will tend towards pyrolysis conditions. As an example: The pile may be 10-feet-wide, by 20-feet-long, but should not exceed 5 feet in height.

▪ Tumblers: Tumblers are usually quite expensive, have to be turned once per day, dry out fairly quickly, and yield a small amount of compost. Additionally, the physical require-ment for turning of the bin is beyond the capabilities of many people.

▪ Purchased plastic bins: Plastic bins are usually priced substantially higher than plastic garbage bins. Therefore, advise clients to purchase a plastic garbage bin and punch some holes in it. Then, they will have something that is roughly equivalent to the purchased plastic bin at a fraction of the cost.

▪ Wire hoops: If a wire hoop is used, it should be constructed of heavy grade concrete wire. This will insure that he unit is sufficiently strong enough to hold the finished compost.

▪ Block Bins: Bins made of con-crete/cinder blocks are acceptable if the mass of the pile does not de-stroy the integrity of the walls.

▪ Pressure-treated wood bins: Pressure-treated wood bins make excellent compost bins. The pH values dissolve the arsenic/chromium compounds and will

kill the microorganisms on the plants prior to anyone ingesting the poisons.

▪ 6-Mil plastic (Wind row): 6-Mil plastic works excellent if you have adequate space, such as a hay field. In this method, organic residue is piled in a strip 6-feet-high, by 6-feet-wide, by up to 80-feet-long. The pile is then wet with water, if necessary, and covered with plastic film. After two months incubation, the finished compost may be removed.

▪ 30 Gallon plastic bag: In this method, the material to be composted is dumped into the garbage bag, wet with a small amount of water, and the top is se-cured. After 2 months incubation, the finished compost may be removed.

How to Construct a Simple Compost Bin

1. Select a suitable spot that is nearly level and is at least 10-inch-wide, by 10-inch-long, and at least 20 feet from any tree.

2. Using salt treated lumber (2”x10”x12’) and (2’x2’x4’), construct a bin 12’x12’x 4’ high on the ground (no bottom).

3. Fill the bin with cleanings collected from a local stable (mixture of horse manure and saw dust). When avail-able, add kitchen scraps and garden-ing refuse to the bin. NOTE: Three pick-up loads of horse manure are required to fill one bin.

4. Allow rainfall to dampen the pile.

5. Cover the pile with a 12’x12’ square of 6-mil black plastic (inhibits animals and UV damage).

6. Allow at least 2 months for the pile to work naturally with no turning.

7. When needed, lift a corner of the plas-tic cover and shovel out the amount desired.

8. Replace the cover to conserve mois-ture if the pile has not been entirely consumed.

Making a Compost Bin

Tomato ring bin. Make a ring of chicken wire at least 3’ high. Throw compost mate-rials inside. Grow tomatoes around and up the outside.

Trash can bin. Use metal or dark colored plastic can with a lid. Drill holes in the bot-

tom and around the side for air circulation.

Loading pallet bin. Wire or screw together loading pallets. You can line the pallets first with ½” hardware cloth to keep smaller materials from falling out.


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Composting with WormsFormally called vermiculture, worm compost-ing is a lot of fun and easy to do indoors when there is no room or no permission to have an outside compost bin. The basic idea is that you are keeping worms as your personal garbage disposal. Special worm bins can be expensive, but it is possible to make your own.

To make a homemade worm compost bin, you will need:

▪ A plastic bin with a top. A minimum of 2 square feet in size is needed. Remem-ber, the bigger the bin, the more worms, the more food waste will be composted

▪ A slightly larger bin or pan that fits underneath the worm bin

▪ Window screen or other fine-mesh metal or plastic screen

▪ Shredded newspaper ▪ Scissors and drill ▪ Food scraps ▪ Red worms/red wigglers. Regular earth-

worms will not work in this environment. Red worms can be purchased through companies that advertise on the Internet.

Figure 23. Worm Composting

Worm composting is a rewarding way for gardeners to see soil organisms transforming garbage into organic mater.

Troubleshooting Compost Problems

Problem: Compost... Suggested Solution

…stays coldMaking hot compost requires volume and some work. The pile needs to be at least 3-feet by 3-feet by 3-feet. Make 6-inch layers, alternating green materials and brown materials. When the pile gets very hot, turn it all over and let it heat up again.

…is too dry Dig a hole in the pile and add wet kitchen scraps. There is no need to water it down with the garden hose. In the future, keep it covered during dry spells. This will keep moisture in.

… has a foul odor Poke it with a shovel to let some air circulate through it. In the future throw some sticks on top of each layer of wet stuff to provide air circulation.

… is made only of browns Add some greens, or just let it be. A pile of leaves will make fine compost all by itself. It might even heat up.

… is made only of greensGreen ingredients all by themselves will rot, but they may stink. Add some newspaper; no more than one quarter of the total material should be paper. Add sticks throughout the pile to permit air circulation.

… is attracting flies Cover kitchen scraps with leaves, or bury them deep in the pile.

… is attracting animals Try using a closed container. In the winter, birds and other animals might sit on the compost to get warm.

…is hosting weeds Either keep the seeds out of the compost or make sure the pile gets hot enough to kill the seeds

….is turning my plants yellow when used in the garden

The microbes are still active and have available nitrogen tied up. The compost was not ready when applied to the garden.


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Uses for CompostBesides the benefits of compost mentioned earlier in this section, compost has many uses. These uses include:

▪ Mulch: Compost makes an effective mulch when spread over the soil surface, around annual and perennial plants, and under trees and shrubs. As little as 1/2-inch of compost spread over the soil sur-face helps to conserve moisture, reduce erosion, protect the soil from temperature extremes, add nutrients to the soil (slow release fertilizer) and suppress weeds.

▪ Planting Medium: A mixture com-prised of four parts compost mixed with one part sand is superior to many purchased potting soils.

▪ Growing Medium: Most crops do well in raised beds to a depth of 6" and grown crops directly in compost. The compost depth of 12" works well for Irish pota-toes, sweet potatoes, carrots and turnips.

▪ Soil Amendment: Cover the area to be tilled to a depth of 4" with compost prior to tilling.

Worm Tips

▪ Worm tea will leak out of the bin into the pan underneath. Make sure to empty the pan so that the liquid does not build up in the bin and drown the worms. You can use the tea as a liquid fertilizer.

▪ Worms are susceptible to overheat-ing or freezing. Try to keep them at room temperature.

▪ Apartment dwellers have been known to keep worm bins under the kitchen sink or in the laundry room. Keep it near the place where food waste is produced.

▪ Make sure other organisms are not co-habiting with the worms. If flies have laid eggs in the worm bin, or other insects are taking over, dis-pose of everything and start over. Try using a more tightly fitting lid on the bin and use a screening to cover the holes in the bin to prevent intruders.

▪ Be persistent. A few helpings of worms may be lost before a suc-cessful worm bin is achieved.

Table 18. Common Compost Myths and Facts

Compost Myths Compost Facts

Compost smells bad When there is too much wet material compost may develop an odor. Poke a smelly compost pile and the smell will become more like clean soil.

Lots of bugs are in the compost pile, and they will hurt the garden

The animals you see in compost – worms, roly-poly bugs, centipedes – are working to decompose the organic matter and make nutrients available to plants.

Compost piles are hard work and must be turned over often

Turning the pile adds air. Adding sticks occasionally will create air pockets and lessen the need to turn the pile

Compost piles must get very hot inside to work properly A cold compost pile will rot, but more slowly than one that gets hot.

Composts must be often watered with the hose to work properly

Moisture can be added from fruit and vegetable peelings, coffee grounds and tea leaves, or gray water- water collected from washing out recyclable cans and bottles

Lime, alfalfa pellets and other amendments have to be added to make the pile rich in nutrients.

There is no need to buy anything to apply to a compost pile. The nutrients from the decomposed organic matter are rich enough.

It is necessary to purchase and add “compost starter”

A shovel of regular garden soil should be added to the compost pile when you start a new pile. After that you can leave it alone. Adding some expired yeast, yogurt or the water from washing out a milk bottle can speed up the process.


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SummarySoil is the basis of plant growth and develop-ment. Without a properly maintained soil, plants will suffer and potentially die. There-fore, it is imperative that, as Master Garden-ers, we teach gardeners to improve and sustain our soil systems. The soil environment must be properly cared for to avoid environmen-tal problems such as: overwatering, which will cause soil erosion and poorly effect plant growth; compaction, which will stunt root growth; and drought, which will negatively effect the plants ability to grow. The first step in doing this is to study and understand the concepts taught in this chapter. Understanding these concepts will help you understand other gardening concepts on your training journey.

Terms to KnowAcre furrow sliceActinomycetesAerationAerobic

AnaerobicAnionsAvailable waterAvailable water-holding capacity (AWHC)BottomlandBufferedCationsClayDecomposersDecompositionDepressionErosionExudatesField capacityFinesFlood plain soilsFootslopeFragipansFriableHardpanHerbivoreHumusLeachingLevelLoamLoppersMacroporesMicroporesMineralizationOmnivoreOrganic MatterOrganic Matter DecompositionOxidationPermanent wilting pointPhysiographic (landscape) positionProtozoaPyrolysisRollingRun-offSandSaturationSiltSoilSoil ConditionerSoil FertilitySoil PhaseSoil ProbeSoil ProductivitySoil StructureSow BugsSpontaneous CombustionSteepTerraceTilthTopography

Tilling

Tilling will speed up oxidization of the compost to carbon dioxide; thus, the benefits do not last as long as if the com-post was applied as mulch.

Troubleshooting

Immature Compost

If the raw materials in your compost are recognizable, the compost is probably not ready for use. If immature compost is used, it will continue to decay. As the mi-crobes consume the raw materials (wood chips, immature compost, etc.), they tie up most of the available nitrogen. This nitrogen will become available to the plants after the microbes have complet-ed their task; however, since they can out compete with your favorite plant for the nitrogen, the plants close to the imma-ture compost will turn yellow/green in color due to lack of nitrogen.


O�cal TMG

InstructorCopy

TranspirationTurgorUndulatingUplandVermiculture

Test Your Knowledge1. List some soil productivity factors and ex-

plain which one is most easily changed.

2. What is the main role of living organisms in the soil?

3. Explain how the classes of slopes A-D are related to erosion potential.

4. What does soil texture affect?

5. What are the “brown” ingredients in compost?

6. What are the “green” ingredients in com-post?

7. What are the most important factors in building a successful compost pile?

8. Explain two ways to aerate a compost pile.

9. Briefly explain the process of nitrogen transformation.

10. How can compost be used in the home garden?

11. Describe the difference between sid-edressing, topdressing and banding for fertilizer application.

ResourcesUniversity of Tennessee Soil, Plant and Pest

Center http://soilplantandpest.utk.eduNRCS Web Soil Survey

http://websoilsurvey.nrcs.usda.govNRCS Soil Education

http://soils.usda.gov/education/

chapter 3 3 soils and plant nutrition ... tennessee master gardener handbook 53 oflcal tmg...

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