unit 4: nutrients chapter 7. unit 4: nutrients unit 4 objectives: understanding of essential plant...
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Unit 4: Nutrients
Chapter 7
Unit 4: Nutrients
Unit 4 Objectives: Understanding of essential plant
nutrients and their roles Nutrient action in the soil Knowledge of soil testing and
interpreting nutrient needs Soil pH and how it affects nutrient
availability Deficiency symptoms
Unit 4: Nutrients Essential Nutrients and their Roles
Chemical elements needed by plants for normal growth and development called nutrients
16 essential elements divided into groups Nonmineral elements
C, H, O H & O supplied from carbon dioxide and water
through photosynthesis Primary Minerals
N, P, K
Unit 4: Nutrients Secondary Minerals
Ca, Mg, S Micronutrients
B, Cl, Cu, Fe, Mn, Mo, Zn
Mineral nutrients supplied by the soil through nutrient uptake
Sugars produced by photosynthesis are responsible for most plant growth
Unit 4: Nutrients
Fertilizers Added to soil to help supply needed
macro- and/or micronutrients N
One of the most abundant and mobile nutrients
Part of every plant cell Soils may contain ~5000 lbs./ac. 78% of Earth’s atmosphere
Unit 4: Nutrients Part of chlorophyll What do we observe when N is lacking?
Starts at the tips of lower leaves Slower growth Spindly stalks and stems
Manufactured most commonly into what form? How is it made? What else can be manufactured?
Unit 4: Nutrients N and the Environment
Very mobile Very susceptible to many physical, chemical,
and biological processes Significant losses are possible
Where does it go? Leaching, erosion, denitrification,
volatilization >50% of all N supplied to the soil may never
be used by the crop Nitrification
Regardless of how N is applied to the soil, it ends up in Nitrate form
Unit 4: Nutrients Process converts ammonium from organic
matter or fertilizers to nitrate Only ammonium not converted is trapped
by soil clays Performed by soil bacteria
Once converted to nitrate, becomes part of soil solution
Leaching Nitrates held only slightly by soil colloids
and humus (why?) Move w/ soil water Ammonium is held tightly in the soil (why?)
Unit 4: Nutrients Nitrate losses during the growing season in
medium and fine-textured soils estimated at <5% (greater in coarse-textured soils)
Erosion Nitrates primarily lost in runoff water Ammonium and organic forms of N lost in
sediment Denitrification
Occurs only under anaerobic conditions Bacteria convert nitrate back to N gas Estimated losses of 15-30% of total applied
N from an area flooded for just 3-5d
Unit 4: Nutrients Losses from well-drained soils usually small
Volatilization Occurs when urea converted to ammonium
carbonate when applied to warm moist soils Breaks down into ammonia gas Lost into atmosphere if this occurs on the
soil surface Usually <10%, but can be great if urea is
topdressed, then followed by 3+d of warm dry conditions
Incorporation or injection will eliminate this loss
Unit 4: Nutrients Nitrogen Cycle
Must be pulled from the atmosphere to be used by plants Fertilizer plants N fixation by green plants
N can take many forms from atmosphere to soil to plant and back
Nitrogen Fixation Elemental N removed from the atmosphere by
soil bacteria called rhizobia Live on nodes of legume plant roots Can provide more N to the soil than they
use
Unit 4: Nutrients Organic Matter (Humus)
Decomposition/decay of plants into soil organic matter
Rate of decomposition & amount of N released depends on C:N ratio <25:1 – plant/animal residues are quickly
converted to large amounts of N that can be used by growing plants
Conversion process called mineralization >25:1 – N is immobilized in the soil,
decomposition is slow, bacteria rob N from the soil, N deficiencies can occur
Unit 4: Nutrients Material that has completely decomposed
called humus C:N ratio of ~12:1 Controls the release of N in soil Humus contains ~5% N Soil w/ 1% organic matter will have ~1000
lbs. N/ac. (only ~2% is available annually)
P Very immobile
Only moves if soil particles move Lost via plant removal and erosion
Unit 4: Nutrients Must be near plant roots to be used Soil Reactions
Soil P amounts closely related to pH Maximum availability at slightly acid pH P will form insoluble compounds w/ other
elements under higher or lower pH’s P Sources
DAP & Triplesuperphosphate are main fertilizer sources DAP generally used in dry bulk fertilizers TSP available in bags/bulk
Unit 4: Nutrients Other sources include:
Animal manure, sludge, plant residues, etc. Mineral Apatite – main source for P fertilizer
manufacturing Mined in: FL, NC, WY, MT, TN
K Second most-used nutrient Also relatively immobile Most common deficiency symptom is
scorching or browning along leaf margins or lower/bottom leaves
Unit 4: Nutrients Soil Reactions
Found in greatest quantity in the soil, available amounts are relatively small Most tied up w/ other soil minerals Considerable amounts trapped between clay
particles K Sources
Most K is mined from deposits found from ancient seas Largest deposit in Saskatchewan, CAN
Muriate of Potash most common source of K fertilizer
Unit 4: Nutrients
Secondary & Micronutrients Just as important for plant growth, but
needed in much smaller amounts S
Most present in organic form Becomes available upon decomposition of
organic matter Mineralized to sulfate form
Subject to leaching and immobilization by microbes
Unit 4: Nutrients May be supplied from atmosphere by rain May be present in some lower-grade
fertilizers as an impurity Gypsum can be used to increase soil S
levels Plants absorb in sulfate form Constituent of amino acids, proteins,
vitamins, enzymes Also contribute to distinct odors
Mustard, onion, garlic Required for N fixation
Unit 4: Nutrients Ca
Supplied by soil minerals, organic matter, fertilizer, lime
Primary ion on CE sites Essential part of plant cell wall structure Helps w/ transport/retention of other
nutrients Provides strength Critical balance w/ Mg and K
Abundance of one can cause deficiencies of the other two
Unit 4: Nutrients Mg
Sources Soil minerals, organic matter, fertilizers,
dolomitic limestone Held on CE sites like Ca, K Part of chlorophyll and essential for
photosynthesis Activates many plant enzymes Relatively mobile in the plant
Can be translocated from older to younger plant parts to prevent deficiencies
Unit 4: Nutrients Micronutrients
Most apt to limit crop growth under several conditions Highly leached acid sandy soils Muck soils Soils high in pH or lime Soils heavily cropped and fertilized w/
macronutrients Fe
Essential for chlorophyll synthesis Part of many plant organic compounds Antagonist w/ Mn
Unit 4: Nutrients Cu
Essential for growth Activates many enzymes Deficiencies interrupt protein synthesis Excess Cu can cause Fe deficiency
Mn Absorbed in ionic form Believed to activate many enzymes Antagonist w/ Fe Availability closely related to soil pH
Deficiencies can occur in slightly acid/alkaline soils
Unit 4: Nutrients Zn
Controls synthesis of indoleacetic acid which dramatically regulates plant growth
Also active in enzyme activity Mo
Important for enzymatic activity, N fixation Inadequate Mo can cause N deficiencies Required in minute amounts
B Regulates the metabolism of CHO in plants Needs vary w/ crop, and high levels may
damage B sensitive crops
Unit 4: Nutrients Nutrient Availability & Plant Uptake
Nutrients must be available in the soil in forms the plant can absorb to be effective
Absorption occurs when plant roots come into contact w/ soil solutions that contain these nutrients
Nutrients held by soil particles Although large amounts of nutrients may be
found in the soil, small quantities are actually available
Unit 4: Nutrients Unavailable nutrients may be found in the
following forms: Insoluble chemical compounds – P and micros Unweathered or Undecomposed soil minerals –
most all nutrients can be in this form Organic Matter or Plant Residues – mostly N or
S Trapped by Soil Particles – lots of K, some
ammonium Greatly affected by soil pH
Unit 4: Nutrients Nutrient Interactions
How one nutrient may help/hinder the uptake of another Conditions may affect Nutrients may also vary
Examples: Ammonium-potassium: ammonium can
interfere w/ K uptake, can create K deficiencies in some crops
K-Mg: K can reduce uptake of Mg at high rates, can result in Mg deficiencies
Unit 4: Nutrients P-N: P uptake increased in presence of N P-Zn: high P can reduce uptake of Zn
Soil pH Acid/base balance of the soil Highly acid/alkaline soils can negatively affect
nutrient uptake and/or production Causes of Acid Soils
High losses of Ca, Mg, K from erosion, leaching, and crop removal
Conversion of ammonium to nitrate results in soil acids
Unit 4: Nutrients Adjusting Soil pH
Can be easily adjusted to any desired range Adjustments should only be made based on
soil test results What would we apply to adjust soil pH
up/down? What are the recommended pH ranges for
some common crops? (See pg. 155) Lime Sources
Most economical source is ag lime
Unit 4: Nutrients Dolomitic – contains Mg
When might we use this? Calcitic – contains only Ca Functions
“Sweetens” the soil (most plants don’t prefer acid soils)
Improves availability of plant nutrients Increases effectiveness of applied N, P, K Increases microbe activity, especially for N
fixation and decomposers Improves plant growth and yields
Unit 4: Nutrients
Soil Testing Most accurate method for determining
fertilizer needs Measures soil pH and available nutrients Most fertilization problems associated w/:
lack of/improper use of N, P, K, and lime
Unit 4: Nutrients Collecting the Sample
Must be a representative sample Take a large composite sample Mix for one representative sample Each sample shouldn’t represent >10 ac.
How do we collect a sample? What are some new technologies being
used?
Unit 4: Nutrients
Foliar Symptoms Vary w/ plant species What other things can produce foliar
symptoms? Suspicion of nutrient deficiencies should
be confirmed w/ other diagnostic methods
Unit 4: Nutrients Tissue Testing
Rapid Tissue Testing Green tissue collected for analysis Chemicals used to test for present elements Accuracy may be sacrificed for speed Dry tissue testing more accurate
Dry Tissue Testing Uses dry leaves or plants Entire leaf ground up and tested for selected
nutrients Should be very accurate
Unit 4: Nutrients More expensive and time-consuming
compared to Rapid Testing or Soil Analysis Plant part sampled and stage of
development critical to interpretation of results
Choosing the Fertilizer Source Many fertilizers available to supply
needed nutrients If fertilizer supplies only one nutrient –
called straight material (urea, muriate of potash)
Unit 4: Nutrients If contain each of 3 primary nutrients –
called complete or mixed fertilizer Can be purchased bag or bulk How do we determine N, P, K amounts in
a fertilizer? What forms are they in?
Solid or Liquid Fertilizer? Performance is equal if equal amounts are
applied Makes little difference to the plant
Unit 4: Nutrients Selection should be made based on:
Availability Economics Other factors
Fertilizer Placement Soil characteristics, crop, nature of
fertilizer material should be considered when determining method of application
Things to consider: Provide adequate nutrient quantities in the
root zone
Unit 4: Nutrients Irregular distribution can lower
effectiveness of fertilizer Early seedling stimulation usually
advantageous – fertilizer should be placed near seedling roots
Rate and distance of fertilizer movement depend on the soil, can be carried up in dry conditions, or down in wet conditions
Fertilization in dry conditions may do more harm than good to the plant
N, K more readily soluble than P and should not be placed in as high a concentration near plant roots
Unit 4: Nutrients Reduction in soil moisture increases salt
concentration and can result in crop injury P should be placed in the root zone due to
immobility Banding fertilizers can reduce rates by 50%
compared to broadcast Slows conversion of P to unavailable forms
Foliar Fertilization Feed plants through leaves, stems, etc. Should only be used in a supplementary role Can only apply in small amounts (why?)
Unit 4: Nutrients Can be expensive Most appropriate to supplement micros
Other Fertilization Sources Animal Manures
Nutrient concentration is generally low, but some quantities of all nutrients are present
Nutrient content may be variable What might affect this?
General Rules of Thumb: ~16T on manure produced/hd/yr regardless of
species
Unit 4: Nutrients Adding superphosphate to manure can reduce
ammonia volatilization Not appropriate for intensive livestock
operations (why?)
Hydroponic Requirements What is hydroponics? Can be especially effective for some
vegetables (spinach, tomatoes) Bath plant roots in nutrient solution
Must be changed weekly due to plant depletion
Unit 4: Nutrients Avoid problems w/ weeds, soil textures,
diseases Must balance all chemical and physical
conditions properly to work All essential plant nutrients must be
supplied in solutions Imbalances of elements can cause serious
problems
Unit 4: Nutrients
Unit 4 Assignment: Chapter Review Questions pgs. 165-166
#’s 6-10, 12-15 Each question 2 points Due next class!