Post on 26-Dec-2019
transcript
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
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
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
Typical Soil Profile
www.timberpress.com
Makeup of Soils
Pore Space
Solid
Organic
Air
Water (sand, silt,
& clay)
Physical Characteristics of Soil
Texture
Structure
Sandy loam Clay loam
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
Soil Texture
The Soil Triangle
(Based on lab analysis)
Soil Particle Sizes
Sand 2.00 to 0.05 mm
Silt 0.05 to 0.002 mm
Clay 0.002 to <0.0002 mm
Soil Texture
Loamy sand LIGHT Sandy loam Loam Silty loam Clay loam Clay Silty clay Sandy clay HEAVY
Soil Texture Affects Soil Moisture
Water Holding Capacity
Permeability
Water Infiltration through Soils
Capillary Water Movement in Clay Loam Soil
• 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)
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
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
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
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
Soil Organic Matter Loss Recent Research
Sources: Univ. of Minnesota, Ohio State Univ.
Humus
• What’s left over after organic matter decomposes
• Cannot be seen by naked eye
• Very reactive (CEC)
• In equilibrium with organic matter additions
Humus, OM, plant & microbial exudates, and earthworm castings act as “binding” agents
Soil Aggregate Formation
• Bacterial polysaccharides, etc. – micro-aggregate formation
• Fungal hyphae – enmeshing micro-aggregates into macro-aggregates
Soil Aggregation
© 2012 Nature Education
http://www.microped.uni-bremen.de/SEM_index.htm
Fungal hyphae growing through the soil
Netlike fungal mycelia can stabilize micro-aggregates
http://www.microped.uni-bremen.de/SEM_index.htm
http://www.microped.uni-bremen.de/SEM_index.htm
Stabilization of Soil Structure by Actinomycete Filaments
Tillage vs. No-Till Effects on Soil Aggregation
No-till Tilled
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
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
A Key Goal = Good Soil Tilth
Soil Structure May Vary Greatly
Good vs. Poor Soil Structure
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
Results of Compacted Soils,
Poor Drainage
De-Compacting Soils
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
Tire Compaction Avoid Traffic on Wet Soil
No compaction, good aggregation
Compaction, no aggregates
Plow Pan
Ripping to break up plow pan
Plow Pan Disked Soil (18 mo. Ago)
Crust Forms on Unprotected Soil Rainfall or Sprinklers
Cemented Hardpan
Water Movement in Soils
Poorly Structured/ Compacted Soil
Well Structured Soil
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
Anatomy of Young Roots
Emerging
lateral
root
Root
hairs
Root
cap
Root
hairs
Cell
elongation
Cell
division
Root cap
Root Hairs
• Cells, not roots!
• Greatly increase root surface area
• Very short lived Nucleus
Root hair
Root Cap
• Covers apical meristem
• Produces slimy “mucigel”
Sugars, enzymes, amino acids
Protects & lubricates root tip
Improves soil aggregate
formation
Source: Laprotox (UFRGS)
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
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.
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
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
Mycorrhizal Fungus
Sources: Bonfante & Genre 2010, Astrid Volder, UCD
Ecto Arbuscular
Mycorrhizal Fungi Ecto-Mycorrhizae
• Grow on trees in pine, oak, beech, birch, and willow families
• Grow outside and between cells of young roots
• 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
Mycorrhizae
Poor growth of
forest trees without
mycorrhizae –
where nutrients are
limited
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.
https://TechInsiderScience/videos/927452267363450/
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
Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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
• 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
• 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
• 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
Nodules Created by Rhizobium Bacteria
Berseem clover
• 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
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
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
Mineralization and Immobilization
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
Timing of N Mineralization vs Crop Demand
Gaskell et al., 2006
Synchronize needs with availability
Apples: Organic N fertilization 4-6 weeks after bloom optimum, highest need
Cheng and Raba, 2009 Courtesy T. DuPont
• 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
Annual Clovers
Subclover
Crimson Rose
● Self reseeding ● Mainly for orchards
and vineyards
• 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
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
• 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
• 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
Cover Crop, Tomatoes
FOHC
Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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
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
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
Organic Amendments
• Composts
• Manures
“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
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
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
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
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
% 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
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)
OSU Organic Fertilizer
Calculator
N. Andrews et al.
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
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
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
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
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.)
Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
Mulching with Wood Chips
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
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
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
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
Mulch alone won’t keep soil in place on steep slopes
Topics to be Covered
• Cover Crops
• Fertilization
• Mulching
• Soil Sampling and Analysis
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
Soil Sampling Tubes (or use shovel)
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.
Sampling Patterns
• 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
THANK YOU!
Questions?