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Secrets of the Soil: Unearth the key to healthy soil, healthy plants
El Dorado County Workshop Nov. 1, 2016
Chuck Ingels
Farm & Horticulture Advisor
http://cesacramento.ucanr.edu
Physical Characteristics of Soil Plant Roots and the Rhizosphere
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Topics to be Covered
• Physical Characteristics of Soil
Soil texture and its effects water & nutrient retention
Soil organic matter and soil aggregation
Soil structure and effects of tilling & compaction
• Plant Roots and the Rhizosphere
Root structure and Rhizosphere
Mycorrhizae
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Topics to be Covered
• Physical Characteristics of Soil
Soil texture and its effects water & nutrient retention
Soil organic matter and soil aggregation
Soil structure and effects of tilling & compaction
• Plant Roots and the Rhizosphere
Root structure and Rhizosphere
Mycorrhizae
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Typical Soil Profile
www.timberpress.com
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Makeup of Soils
Pore Space
Solid
Organic
Air
Water (sand, silt,
& clay)
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Physical Characteristics of Soil
Texture
Structure
Sandy loam Clay loam
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Soil Texture vs. Structure
Texture: Percent sand/silt/clay
• Examples: sandy loam, clay loam
Structure: Arrangement of particles into aggregates, clods, crusts, pans, etc.
• Affected by compaction
Impractical to change
Can be changed – for better or worse
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Soil Texture
The Soil Triangle
(Based on lab analysis)
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Soil Particle Sizes
Sand 2.00 to 0.05 mm
Silt 0.05 to 0.002 mm
Clay 0.002 to <0.0002 mm
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Soil Texture
Loamy sand LIGHT Sandy loam Loam Silty loam Clay loam Clay Silty clay Sandy clay HEAVY
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Soil Texture Affects Soil Moisture
Water Holding Capacity
Permeability
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Water Infiltration through Soils
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Capillary Water Movement in Clay Loam Soil
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• A measure of soil fertility (soil analysis)
• Cations in soil solution in dynamic equilibrium with clay & humus particles
• Varies by soil type and % organic matter
Cation Exchange Capacity (CEC)
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CEC 1-10
• High sand content
• N & K leaching more likely
• Less lime or sulfur needed to adjust pH
• Low water-holding capacity
High vs. Low CEC
CEC 11-50
• High clay or OM content
• Greater capacity to hold nutrients
• More lime or sulfur needed to adjust pH
• High water-holding capacity
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Typical CECs Based on Soil Texture
Soil Texture Typical CEC Range
meq/100g
Sand 2 – 6
Sandy Loam 3 – 8
Loam 7 – 15
Silt Loam 10 – 18
Clay & Clay Loam 15 – 30
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Topics to be Covered
• Physical Characteristics of Soil
Soil texture and its effects water & nutrient retention
Soil organic matter and soil aggregation
Soil structure and effects of tilling & compaction
• Plant Roots and the Rhizosphere
Root structure and Rhizosphere
Mycorrhizae
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Soil Organic Matter • Serves as energy source
(food) for microbes, which promote aggregation
• Essential nutrients are obtained by plants as OM decomposes
• Enhanced by OM additions but destroyed by cultivation
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Soil Organic Matter Loss Recent Research
Sources: Univ. of Minnesota, Ohio State Univ.
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Humus
• What’s left over after organic matter decomposes
• Cannot be seen by naked eye
• Very reactive (CEC)
• In equilibrium with organic matter additions
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Humus, OM, plant & microbial exudates, and earthworm castings act as “binding” agents
Soil Aggregate Formation
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• Bacterial polysaccharides, etc. – micro-aggregate formation
• Fungal hyphae – enmeshing micro-aggregates into macro-aggregates
Soil Aggregation
© 2012 Nature Education
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http://www.microped.uni-bremen.de/SEM_index.htm
Fungal hyphae growing through the soil
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Netlike fungal mycelia can stabilize micro-aggregates
http://www.microped.uni-bremen.de/SEM_index.htm
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http://www.microped.uni-bremen.de/SEM_index.htm
Stabilization of Soil Structure by Actinomycete Filaments
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Tillage vs. No-Till Effects on Soil Aggregation
No-till Tilled
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Topics to be Covered
• Physical Characteristics of Soil
Soil texture and its effects water & nutrient retention
Soil organic matter and soil aggregation
Soil structure and effects of tilling & compaction
• Plant Roots and the Rhizosphere
Root structure and Rhizosphere
Mycorrhizae
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Soil Structure
Structure - the arrangement of soil particles into aggregates
Good structure: holds water (micropore space) and has air space (macropore space)
Poor structure: lacks adequate macropore space
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A Key Goal = Good Soil Tilth
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Soil Structure May Vary Greatly
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Good vs. Poor Soil Structure
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Effects of Compaction on Soil
• Soil structure is destroyed – pore space is severely reduced
• Soil drains slowly and is prone to being anaerobic
• Compacted soil physically impedes root growth
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Results of Compacted Soils,
Poor Drainage
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De-Compacting Soils
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Some Soil Layers Restrict Air, Water, and Root Penetration
• Hardpan – cemented (by silica, iron, carbonates)
• Traffic or compaction pan – caused by vehicles, tillage implements, feet, hooves
• Crust – brittle, compact/hard when dry
• Claypan – higher clay than overlying layer
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Tire Compaction Avoid Traffic on Wet Soil
No compaction, good aggregation
Compaction, no aggregates
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Plow Pan
Ripping to break up plow pan
Plow Pan Disked Soil (18 mo. Ago)
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Crust Forms on Unprotected Soil Rainfall or Sprinklers
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Cemented Hardpan
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Water Movement in Soils
Poorly Structured/ Compacted Soil
Well Structured Soil
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Topics to be Covered
• Physical Characteristics of Soil
Soil texture and its effects water & nutrient retention
Soil organic matter and soil aggregation
Soil structure and effects of tilling & compaction
Plant Roots and the Rhizosphere
Root structure and Rhizosphere
Mycorrhizae
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Anatomy of Young Roots
Emerging
lateral
root
Root
hairs
Root
cap
Root
hairs
Cell
elongation
Cell
division
Root cap
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Root Hairs
• Cells, not roots!
• Greatly increase root surface area
• Very short lived Nucleus
Root hair
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Root Cap
• Covers apical meristem
• Produces slimy “mucigel”
Sugars, enzymes, amino acids
Protects & lubricates root tip
Improves soil aggregate
formation
Source: Laprotox (UFRGS)
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Plant Roots Feed the Microbes! • Use 25-40% of carbohydrate supplies to feed microbes
• Use hormones to attract and “farm” bacteria, fungi, and other organisms to help recycle soil nutrients & water
Sources: 1. J. Hoorman, Ohio State Univ. 2. www.nature.com
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The Rhizosphere
• Thin region of soil that is directly influenced by root secretions (exudates) and soil microbes
• Roots release organic substances into the rhizosphere
• There are over 1000 times more microbes associated with a live root than in the bulk soil
Source: J. Hoorman, Ohio State Univ.
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Topics to be Covered
• Physical Characteristics of Soil
Soil texture and its effects water & nutrient retention
Soil organic matter and soil aggregation
Soil structure and effects of tilling & compaction
Plant Roots and the Rhizosphere
Root structure and Rhizosphere
Mycorrhizae
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Mycorrhizae (“Fungus-Roots”)
• Fungal infection of roots – symbiotic relationship
• Fungi – receive sugars; Plants – phosphorus & water
• Help roots explore up to 20x the volume of soil
Increases plant resistance to drought
• Lacking only in sedges & brassicas (cabbage fam.)
• Poor growth without myc. where nutrients limited
• Soil inoculation helpful only in poor/disturbed soils
• Two main types: Ecto- and endo-mycorrhizae
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Mycorrhizal Fungus
Sources: Bonfante & Genre 2010, Astrid Volder, UCD
Ecto Arbuscular
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Mycorrhizal Fungi Ecto-Mycorrhizae
• Grow on trees in pine, oak, beech, birch, and willow families
• Grow outside and between cells of young roots
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• Most important is vesicular-
arbuscular myc. (VAM or AMF)
Vesicle = bladder-like structure
Arbuscule = branched structure
• 80% of plant species
• Most crops (monocots & dicots),
hardwoods, non-pine conifers
Mycorrhizal Fungi Endo-Mycorrhizae
Infection directly into root cells
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Mycorrhizae
Poor growth of
forest trees without
mycorrhizae –
where nutrients are
limited
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Add Mycorrhizal Inoculants?
• Plants often choose fungi selectively
• Research shows that the wrong fungi, or wrong combination, can impair plant growth
• Adding purchased AMF not wise:
– Often dead in the bag
– May not be the correct species
– Adding fungi has unknown effects on the growth of that plant, the soil organisms in your area, etc.
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https://TechInsiderScience/videos/927452267363450/
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Chuck Ingels
Farm & Horticulture Advisor
http://cesacramento.ucanr.edu
Practices to Protect and Enhance Soils
Secrets of the Soil: Unearth the key to healthy soil, healthy plants
El Dorado County Workshop Nov. 1, 2016
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Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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Cover Crops Definitions
Cover crop
• A non-harvested crop planted to provide any of a number of benefits, such as improving soil quality, reducing erosion, adding N, and/or attracting beneficial insects
Green manure cover crop
• A crop grown & plowed under for its beneficial effects to the soil and subsequent crops
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• Lowest fertilizer energy use: On-site production of N
May still need additional N
• Add organic matter
• Improve soil tilth and water penetration
Cover Crops Benefits
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• Competition with trees for water & nutrients
• Insect and vertebrate pests
• Increased costs and management
• Additional equipment required
• Requires chopping/disking in spring
Cover Crops Potential Problems
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• Atmosphere = 78% N; only legumes can use
• Rhizobium bacteria in roots use N in soil air
Symbiotic relationship
Store N in nodules on roots
Nodules resemble root-knot nematodes
• Most N translocated to foliage
Cover Crops Nitrogen Fixation of Legumes
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Nodules Created by Rhizobium Bacteria
Berseem clover
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• Low ratios (legumes) – rapid decomposition, net release of N
• High ratios (cereals/grasses) – slow decomposition, & net tie-up of N
Cover Crops C/N Ratio
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Example of C/N Ratios
Oat straw 70:1
Wood chips 60:1
Corn stubble 57:1
Rye (mature) 37:1
Rye (vegetative) 26:1
Mature alfalfa hay 25:1
Source: J. Hoorman, Ohio State Univ.
Ideal microbial diet 24:1
Rotten manure 20:1
Legume 17:1
Young alfalfa hay 13:1
Hairy vetch 11:1
Soil microbes (avg.) 8:1
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Cover Crops General C/N Ratios
RESIDUE C/N RATIO
Legume 15:1 to 20:1
Brassica 20:1 to 30:1
Grass 40:1 to 80:1
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Mineralization and Immobilization
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C:N Ratio of Organic Matter
• As a rule of thumb:
• At C:N >20:1, NH4+ is immobilized (tied up)
• At C:N < 20:1, NH4+ is mineralized (released)
N in organic matter and microbes
NH4+
(ammonium)
C:N < 20:1
C:N > 20:1
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Timing of N Mineralization vs Crop Demand
Gaskell et al., 2006
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Synchronize needs with availability
Apples: Organic N fertilization 4-6 weeks after bloom optimum, highest need
Cheng and Raba, 2009 Courtesy T. DuPont
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• Standard winter green manure legume mix:
High N mix: Bell beans, vetch, and field peas
Add for soil tilth (or use alone): Oats or barley
• Annual reseeding mix (orchards & vineyards):
Crimson, rose, subclover + bur medic
• Summer:
Cowpeas, buckwheat
Cover Crops Species
Vetch/Pea/Oat Mix
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Annual Clovers
Subclover
Crimson Rose
● Self reseeding ● Mainly for orchards
and vineyards
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• Good seedbed preparation; inoculate seed
• Scatter seed and rake in (or drill)
• Rototill 3-4 weeks before planting spring crop
Reduced soil-borne diseases
Reduced tie-up of soil N
Cover Crops Planting and Incorporation
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Inoculating Legume Seeds
Background
• Specialized bacteria (Rhizobium sp.)
Not to be confused with Mycorrhizae
Creates nodules on roots
Captures N in plant, most moves into foliage
• Insures that N fixation will occur
• Not essential to inoculate for same soil in year 2
• Good to inoculate garden peas & beans too
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• Use at least 1 oz./10 lbs. of seed
• To help inoculant adhere to the seed:
Mix 9:1 hot water (non-chlor.) + corn syrup
Let cool, add a small amount to seeds
Rate effect (up to a point) – Use plenty!
• Pouring dry into hopper may work but would not provide uniform application
Inoculating Legume Seeds
Methods
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• Grass alone may require N
• Avoid N fertilizers on legumes
High soil N legumes fix little N
• Max. N contribution is at early flowering (incorporate in March)
• >80% of N is in above-ground parts; <20% in roots
Cover Crops Nutrition
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Cover Crop, Tomatoes
FOHC
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Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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Vegetable Fertilization Veg. Gardening Basics, UC Pub. 8059
• Preplant: N-P or N-P-K
Use 1/3 lb. N per 100 sq. ft.
Dry steer manure: 100 lb. per 100 sq. ft.
Chicken manure: 20 lb. per 100 sq. ft.
• Side dressing when plants 3-4” high
0.4 lb. N per 100 sq. ft.
Banded application
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Fruit & Nut Tree Fertilization The Home Orchard, UC Pub. 3485
• Total lbs. of N/year to correct a deficiency:
Large fruit tree: 1 lb.
Small fruit tree: 0.5 lb.
Large nut tree: 2 lbs.
Small nut tree: 1 lb.
• Deciduous trees: Late spring and summer
• Citrus: Jan. or Feb., May
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Synthetic vs. Natural Fertilization
• Plants take up nutrients from natural and synthetic sources (no preference)
• Natural fertilizers feed soil microbes and require them for breakdown
• Microbes (and roots) release compounds like organic acids, enzymes, and chelates convert nutrients from organic form into a plant-available (soluble) form
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Organic Amendments
• Composts
• Manures
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“Finished” Compost
• Thermophilic heating process with turning
• Temperature low, no ammonia smell
• Contains diverse microbial populations
• Contains most nutrients required by plants
• Should not contain weeds & plant pathogens
• N content usually 1-1.5%, very slow release
• Usually considered a soil amendment to add organic matter, not fertilizer
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Earthworm Castings Better than Compost?
• Both add slow-release nutrients, improve soil structure, increase water & nutrient retention
• Earthworm castings may be better for:
– Promoting beneficial microbial activity
– Adding more humic acid to stimulate plant growth
– Improving soil aggregation
• Using compost and some EW castings ideal
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Manures
• Fresh/dried manure
N content & release generally higher than compost
Food safety concerns: Do not use on leafy greens
Orchards: Cannot be used within 90 days of harvest
Strong odors
Salinity concerns
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Manures Characteristics and Uses
• Poultry, dairy, feedlot, steer, rabbit, sheep/goat
• May contain salts and weed seeds
• N content varies greatly
Poultry may have >3%N (ammonia smell)
Aged feedlot manure may have <1% N
• Use caution!
Match N need with plant demand, consider N loss
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Application Strategy: Incorporation…
Poultry manure
Other manure
The same day 0.75 0.50
Within 1 day 0.50 0.40
Within 2–4 days 0.45 0.35
Within 5–7 days 0.30 0.30
After 7 days/none 0.15 0.20
Volatilization % of N Retained
Courtesy T. DuPont
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% Dry Weight Basis
Manure N P K
Chicken, fresh 5.1 2.0 1.8
Chicken, partially
composted
2.9 3.3 3.3
Steer 2.5 0.4 0.7
Horse 1.8 0.5 1.2
Manures Typical Nutrient Content
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Available N from Manures, Compost Decay Series
• UC research, 1970s
• Average plant-available N over 3 years
(years 1, 2, and 3):
Chicken (90%, 10%, 5%)
Dairy (75%, 15%, 10%)
Feedlot (35%, 15%, 10%)
Compost (~10% in year 1)
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OSU Organic Fertilizer
Calculator
N. Andrews et al.
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Guidelines for PAN, Year 1
Year 2 PAN – 5-10% of total initial N
Compost – 2%/yr N mineralization from Yr 4 on (Cogger et al.)
Nitrogen % C:N ratio % N Available
Fresh Material
1 35 0
2 18 15
3 12 30
4 9 45
5 7 60
6+ <6 75
Composts
1 25-35 5
2-3 10-15 10
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Amendment
%N
% PAN, Season
DW Basis
PAN, Season Lb. N/100 lb.
“As Is”
Feather meal 13 75 10
Blood meal 12 75 9
Fish meal 10 75 8
Soy bean meal 7 75 5
Composted manure
1.5 10 0.2
Org. Fertilizer Calculator
PAN of Selected Organic N Fertilizers
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Animal-Based Organic Fertilizers
• Blood meal 13-1-0.6 (80% protein)
Quick N release – ammonia can burn plants
• Bone meal (1-13-0 to 4-12-0, + 22% Ca)
Hi P good for flowers, roots
• Feather meal (usually 12-0-0)
• Fish products
• Many forms, N + some P, K, & micros
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Animal-Based Organic Fertilizers
• Bat/seabird guano
From islands in Pacific & other oceans
– Loss of bats & biodiversity
Bat guano: 3-10% N, up to 12% P, 1% K
Seabird guano: Up to 12% N & P, 0-2% K
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Plant-Based Organic Fertilizers
• Soybean meal (7-0-0)
• Cottonseed meal (6-2-1)
• Alfalfa meal (2-1-2)
• Kelp/seaweed (little N-P-K, mainly used for micronutrients, hormones, vitamins, etc.)
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Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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Mulching with Wood Chips
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Potential Benefits of Mulch
• Reduces weeds & erosion
• Insulates roots from temp. extremes
• Conserves soil moisture ↑ root growth
• Increases microbial activity
• Increases water penetration
• Improves plant establishment
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Potential Problems with Mulch
• May prolong saturation in heavy soils
Favors root and crown rot
• May host plant diseases, insects, and nuisance fungi
• Some wood chips poor quality
• Can’t see soil moisture
• Time consuming to spread
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Mulch Basics
• Wood chips for perennial crops
Conifer mulches last longest
Application rate: 2-4 in. deep
• Non-woody mulch for vegetables
Straw, hay, leaves, compost, etc.
Can incorporate or remove at end of season
• Keep mulch on top of soil to prevent N tie-up
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Do Wood Chips Affect Soil Nutrients?
• Tie-up of N?
N immobilization from high C:N mulch
Generally N tie-up at interface only
Avoid mulch in planting holes
• Soil pH (pine needles acidic) – little effect unless incorporated
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Mulch alone won’t keep soil in place on steep slopes
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Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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Soil Nutrient Analysis
• Doesn’t always tell what plants take up
• Leaf tissue analysis to compliment soil
• Good for baseline info, detecting deficiencies
• Areas that test high may need less fertilizer than other locations
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Soil Sampling Tubes (or use shovel)
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Soil Sampling for Nutrient Analysis Take 20 Cores Per Sample
• Single sample from area of uniform soil
• 2+ samples from different areas
• Sample different soil types separately
• Avoid unusual "patches“
• After disking crop, before fertilizing
• Sample to depth of root zone
– E.g., 0-8” or 0-6” + 6-12” or 0-12” + 12-24”, etc.
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Sampling Patterns
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• Place core samples in bucket, mix soil
• Fill a 1-qt. Ziploc bag 1/2 to 2/3 full
• Label with name, address, & sample site
• Include: Total N, NO3-N, P, K, Ca, Mg, soil texture, pH, OM, CEC, salts(?)
• Soil & plant tissue testing labs:
http://cesonoma.ucanr.edu/viticulture717
– Click on Viticulture Publications, under “Misc.”
Soil Sampling for Nutrient Analysis Send Samples to Lab
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THANK YOU!
Questions?