southern sawg - basic organic soil management
TRANSCRIPT
Basic Organic Soil Management: Caring for the Soil as a Living System
Southern Sustainable Agriculture Working Group Annual Conference
Mobile, AL – January 18, 2014
“Feed the soil, and the soil will feed the crop”
David O’Neill of Radical Roots Farm in central Virginia maintain a healthy, living soil, the foundation of successful farming.
Part One
Feeding and Protecting the Soil
• Conservation – prevent erosion losses• Soil life – the “livestock” on every farm• Habitat – organic matter and tilth
First, keep the soil on the farm!
Once the topsoil is gone, it’s gone (left). Nature builds an inch of topsoil every 300 – 500 years. Yet, good soil conservation and organic soil management can restore fertility in three to ten years (above).
Four Principles of Soil Health
• Keep soil covered as much of year as possible.• Maximize living roots in the soil profile.• Minimize soil disturbance.• Energize the soil system with biodiversity.
– Multi-species cover crops - 5 or more species from 3 or more plant families
Based on the work of the NRCS Soil Health Team in Greensboro, NC – David Lamm, Ray Archuleta, Steve Woodruff, and Terry Briscoe
Key Elements of the Soil Food Web
Multiple trophic levels convert residues to soil organic matter
Plant Roots Play a Vital Role in the Soil Food Web• Root exudates
and fine roots• Rhizosphere
community• Mycorrhizal
fungi
The Organic Matter Cycle
The soil food web is the engine of soil fertility and plant nutrition. The breakdown of organic residues is the sole source of plant nutrients, except for nitrogen fixed by microbes.
N-P-S
The Organic Matter Cycle in Nature
The organic matter cycle provides all the nutrients for plant growth in natural ecosystems such as this forest.
The Organic Matter Cycle in Agriculture• Harvest removes
organic matter (OM) and nutrients.
• Bare soil periods reduce OM input.
• Tillage burns up OM and promotes nutrient leaching.
Replenishing the Organic Matter Cycle
To make up for these losses and maintain soil health, feed the soil life a “balanced diet” of:
• Cover crops and green manures• Compost• Organic mulches• Crop residues• Manure• Organic fertilizers and amendments
Cover Crops: the Cornerstone of Sustainable Crop Production
Cover crops maintain soil quality by:
• Preventing erosion, compaction, crusting
• Adding organic matter• Feeding the soil life
while alive (root exudates)
after terminationTriticale + Field Pea
Cover Crops: the Cornerstone of Sustainable Organic Crop Production
Cover crops provide and manage nutrients by:• Fixing N (legumes)• Scavenging surplus N• Making scarce P (legumes,
buckwheat) and K (grasses) more available
• Not aggravating P or K excesses when these exist
Crimson Clover
Cover Crops: the Cornerstone of Sustainable Organic Crop Production
Cover crops reduce pest problems by:
• Suppressing weeds• Breaking pest and
disease life cycles• Providing habitat for
beneficial organismsBuckwheat
Living Plant Cover is Vital to Soil Health
Bare soil is hungry, stressed, and at risk (not “resting”) …
and is an invitation to weeds.
Minimize bare fallow periods in crop rotations.
Living Plant Cover is Vital to Soil Health
This vigorous cover crop supports a thriving soil food web through abundant root exudates and sloughing of fine roots. This is the right way to “rest” the soil. Winter Rye + Hairy
Vetch
Managing High Biomass Cover Crops
Pearl millet + sunnhemp: 7 feet, 4 tons/ac in 65 days.Mow, scythe, or weed-whack top growth.Using clippings as mulch or to make compost.Till stubble as needed to prepare ground for next crop.
Compost: a Concentrated Soil Food Web
Composting facilitates the conversion of raw organic residues of plant and animal origin into active organic matter and humus by mixing materials in a pile or windrow,, and managing temperature, aeration, and moisture.
Composting Tips
• Start with diverse mix of organic materials.• Balance carbon & nitrogen – C:N ratio 25-35:1
Use 2 – 3 parts plant matter and 1 part manure.• Maintain optimum moisture – 50 – 60%. • Turn windrow to aerate and compost all parts.• Heating to 135 – 150°F for 15 days kills pests,
pathogens, weed seeds. Avoid temps > 150°F• Cool curing period (2-6 months) builds beneficial
microbiota.
Good, finished compost provides:
• Inoculum of beneficial soil organisms
• Active organic matter• Stable humus• Nutrient and moisture
holding capacity• Slow-release nutrients• Extra P, also K, S,
micronutrientsFinished compost producedat Poplar Manor Enterprisesin Riner, VA
Manure: the Original Organic Fertilizer
Manure benefits:
• Provides N, P, K, and micronutrients.
• Supports beneficial soil life.
• Promotes heating and provides nutrients in compost pile (20-30% of total mix).
Manure cautions:
• Unstable N• Pathogens• Antibiotic and herbicide
residues• Weed seeds• Salts• Unbalanced N:P ratio• Cu and Zn buildup
(poultry litter)
Manure Management• Know the source, avoid chemical residues.• Compost or age with carbon (e.g. bedding) to
stabilize nutrients and reduce pathogens.• Compost at ≥131°F for 15 days, or apply at least 120
days before harvest to protect food safety.• Spread on heavy feeding cover crop.• Adjust rates to optimize soil P and other nutrients.• Avoid nutrient runoff – do not spread on bare or
frozen soil on sloping fields near streams or ponds.
Organic Mulch: Simulating Nature’s Way of Feeding the Soil
Organic mulches:• Protect the soil surface.• Conserve soil moisture.• Suppress annual weeds.• Feed the soil life.• Provide slow-release
nutrients.• Provide habitat for
spiders and other generalist pest predators.
Eggplant thriving and nearly weed-free in straw mulch atDayspring Farm in theTidewater of Virginia
Mulching cautions:
• Weed seeds• Herbicide residues in hay (especially
picloram, clopyralid, aminopyralid, aminocyclopyrachlor)
• Cooler soil• Potential pest habitat (slugs, squash bugs)• Excess K with heavy use (esp. grass hay)• Costs of purchase, hauling, and spreading
Plastic Mulch
• Better weed control • Warms soil• Practical at farm scaleHowever:• Does not feed soil life,
may stress earthworms and other organisms
• Planting holes and alleys need other weed control.
• Must be removed at end of season
Black plastic film warms soil and suppresses weeds nearcrops. Alley weeds must be controlled by other means.
Building and Protecting SoilWhile Using Plastic
Covering alleys with organic mulch (above) or a rye + clovercover crop (right) protects soil inalleys and adds organic matter.
Soil Health Challenges for Vegetable Production in the South
• Many vegetable crops return little residue to feed the soil life.
• Farmers working small acreages must crop intensively to make a living, have less flexibility to include soil building cover crops.
• Warm, rainy climates accelerate organic matter oxidation in Southern region soils, especially in tilled annual cropping systems.
The Organic Grower’s Dilemma• Organic producers aim to
build soil life and organic matter for long term fertility.
• Without herbicides, organic systems depend on tillage and cultivation to manage weeds and cover crops.
• Tillage burns up organic matter, and each pass stimulates more weed seeds to germinate.
Plowing down vetch coverreleases N, but leaves thesoil exposed, and may causea flush of weed emergence.
Tips for Maintaining Soil Quality while Growing Organic Vegetables
• Keep soil covered with living plants – as soon as one crop is harvested, plant the next!
• Include one high-biomass, multi-species cover crop per year in the rotation.
• Reduce tillage whenever practical.
Crop rotation and intercropping in a short growing season
In central Vermont, Eliot Colemanmaximized year-round groundcoverage by interplanting covercrops into vegetables at mid-growth.
Reducing tillage to save organic matter
Reduce tillage when practical:
• No-till into rolled-down cover crops
• Mulch tillage (≥30% residue coverage)
• Ridge tillage (skim top of ridge to plant crop)
• Strip-till (disturb soil only in crop row)
Demonstration of no-till vegetable transplanter in roll-crimped cerealgrain cover crop at North Carolina Agriculture & Technology State U.
Perennial sod to restore soil and reduce weed populations
Include perennial sod crops in the rotation to restore soil quality and reduce weed seed populations.
• Cereal grain + red clover for 1 year
• Perennial grass + legume for 2 – 4 years After several years’ vegetables,
oats + red clover were planted. Clover was grown for one year after oats were harvested.
On slopes greater than 5 – 7%, grow perennial crops
At Virginia Gold Orchards, 28 acres of Asian pears on hillyground in Lexington, VA, Paul and YoungSuk Estabrook combines a high-value crop(left) with soil conserving perennial sod between rows of trees (right).
Part Two
Feeding the Crop
• Meeting crop nutritional needs• Optimizing efficiency, avoiding
pollution• Understanding soil tests • Developing organic recommendations
Can “Feed the Soil” adequately feed the crop?
• Healthy, well-fed soil food web can meet most of the crop’s nutrient needs.
• Usually need some nutrient inputs.• NPK input needs are often less than
conventional recommendations.• Replenish organic matter to maintain soil life.
How the Soil Life Modulates Crop Nutrition
Nitrogen is initially tied up as microbes digest fresh residues, then gradually released as higher trophic levels consume microbes.
Organic Nutrient Management
Use organic and natural mineral amendments to:• Restore depleted soils• Remedy nutrient deficiencies & imbalances• Adjust soil pH• Meet nutrient demand of heavy feeders• Replenish nutrients removed in harvest
Determining Fertilizer Needs: Soil Test
A soil test is a “snapshot” of the chemical condition of the soil, including:• pH (acidity)• Plant-available P, K, Ca, Mg, micronutrients• Organic matter content• Cation exchange capacity (CEC)• Recommendations for lime, nitrogen (N),
phosphate (P2O5), potash (K2O)
Interpreting the Soil Test
• VL = very low critically deficient
• L = low likely yield limiting
• M = medium possibly yield limiting
• H = high optimum for most crops
• VH = very high possibly excessive
Understanding conventional nutrient recommendations
• Lime recommendations based on soil pH, CEC, and buffer index.
• NPK recommendations based on research into crop responses to nutrients on conventionally managed soils.Usually more than harvest removal, because some of
applied soluble NPK is lost or tied up.Biologically active soils often need less inputs.
• Can use organic fertilizers to provide recommended nutrients.
Research-based Nutrient Recommendations↓= most profitable application rates.
In healthy, biologically active soils, less nutrient may be needed for optimum response.
Nutrient Sufficiency
• Adequate nutrient reserves in soil.
• Abundant and balanced soil life.
• Deep, open soil profile; roots explore large volume of soil.
Nutrient Deficiency
Scenario 1: the nutrient itself is scarce in the soil.
Apply nutrient
Adjust soil pH if needed to enhance nutrient availability.
Nutrient Deficiency
Scenario 2: The soil life is depleted or unbalanced.
Utilize high quality compost to provide inoculum.
Provide organic inputs to “feed” soil life.
Nutrient Deficiency
Scenario 3: Soil compaction restricts root growth.
Chisel plow or subsoil.
Grow deep-rooted cover crops.
Tips on Using a Soil Test in Organic Nutrient Management
• Correct sampling procedure is important.
• Note deficiencies, excesses, and imbalances.
• Observe the soil and crops.
• Verify with plant tissue analysis.
• Re-test with same lab to monitor trends.
Soil pH and Lime
• Most vegetables prefer pH 6.0-7.0.• Blueberries prefer pH 4.8-5.2.• Use high-calcium limestone if Mg is high.• Use dolomitic limestone if Mg is low.• Use elemental sulfur to lower pH.• Hydrated lime and quicklime are hard on soil
life; not allowed under NOP certification.
Nitrogen (N)• N is most common crop nutrient
deficiency.• Vast stores in atmosphere (N2),
and soil (organic matter N)• Plants utilize soluble nitrate
(NO3-) or ammonium (NH4
+).• Soil life mediates N availability
and storage.• Legumes important N source.• Soluble N easily leached or
volatilized, can pollute water.Deficiency: older leaves turn evenly yellow.
Carbon-to-Nitrogen (C:N) Ratio and Soil N Dynamics
• Soil life utilizes 25-30 lb C for every lb N.
• Organic residues with C:N > 30:1 tie up N.
• Organic residues with C:N < 25:1 release N.
• Materials with C:N 25-35:1 build most soil OM.
• Biological processes reduce C:N of materials.
Organic and natural mineral N sourcesLegume cover crops (can add 50-200 lb/ac)Feather meal (13-0-0) Blood meal (12-0-0) Chilean nitrate (16-0-0)
N sources with some P and K:Cottonseed meal (6-2-1) Fish Meal (9-3-1)Harmony (poultry litter) (5-4-3) Composted manure (~ 1-1-1 to 2-2-2)
Nitrogen Budgeting in Organic Farming
Estimate N available to the current crop:• Estimate N from mineralization by soil life (50 –
200 lb/ac-year – released most efficiently during warm season)
• Legume cover crops (~50% of total N)• Manure (~50% of total N)• Compost (10-25 % of total N)
Apply organic N fertilizers as needed
Phosphorus (P)• Plants use soluble phosphates.• Most soil P = insoluble mineral
and organic forms.• Soil life mediates P availability;
mycorrhizae play vital role.• P excesses initially “fixed,”
then accumulate in soil.• P is lost in runoff and erosion,
can pollute surface waters.• P is most limiting worldwide.
Deficiency: stunted growth, purple or reddish leaves
Organic and natural mineral sources of P
Rock or colloidal phosphates (0-3-0) total (0-20-0) available over ~10 yrs Bone meal (2-14-0) – faster releaseManure, fresh or composted, 1-2% P2O5
Composted plant matter, 0.2-0.8% P2O5
Poultry litter based fertilizers (Harmony, 5-4-3)
1 lb P2O5 = 0.44 lb P
Nitrogen-Phosphorus Balance
• Plants utilize N and P in a ratio of 6:1 – 10:1.• Manure and compost provide N and P at
about 3:1.• Some manure N is lost, P is stable.• Using manure or compost for N can build up P.• Excessive soil P can inhibit mycorrhizae, upset
plant nutrition.• Legume cover crops add N but not P.
Managing N and P in organic systems
If soil P is low:• Compost can be used
generously, 10-20 t/ac annually, to provide N and build organic matter
If soil P is high: • Limit compost to match P
inputs with P removal – about 2-4 tons/ac-year
• Use legumes, blood meal, feather meal, etc. for N
Broccoli requires 150 lb N/ac within 60-70 days after planting. Supplying it all with manure or compost will build up soil P.
Potassium (K)
• Plant-available K as K+ ions, held on CEC (clay + humus).
• Most soils have large insoluble mineral K reserves.
• Cereal grains, grasses, trees release some mineral-fixed K.
• Vegetables use a lot of K (≥ N).• K surpluses can build up in most
soils.• K can leach from sandy soils; not
considered polluting.
Deficiency: white spots, singed or tattered edges on older leaves
Organic and natural mineral sources of K
Potassium sulfate (0-0-51-18S, rapid release) Sul-po-mag (0-0-18-11Mg-22S, rapid release) Greensand (7% K, very slow release)Grass hay mulch (~2% available K) (spoiled hay sometimes available free)
Liquid K foliar fertilizers available (6% K)
1 lb K2O = 0.83 lb K
Potassium and Nutrient Balance
• Hay or grass mulches are very rich in K.
• Excess K can interfere with Mg or Ca nutrition: Blossom end rot, tip burn in vegetables. Grass tetany in livestock (life-threatening).
• K excesses are fairly easy to draw down.
Magnesium (Mg)
• Plant-available Mg is mostly held on CEC as Mg+
+ ions.• Deficiencies occasionally
occur.• Magnesium sources:
Dolomitic lime Sul-po-mag (also adds K)Magnesium sulfate Deficiency: older leaves
yellow between veins.
Calcium (Ca)• Plant-available Ca held on CEC as Ca++ ions.• Ca is usually sufficient if soil pH ≥ 6.0.• Blossom end rot (tomato, pepper) and tip burn
(greens) are localized Ca deficiencies.• Sources of Calcium:
– High calcium limestone, aragonite (raises pH)– Dolomitic limestone (raises pH, also adds Mg)– Gypsum (does not affect pH, also adds sulfur)– Poultry litter based fertilizers (~9% Ca, raises pH)
Sulfur (S)• Most topsoil S in organic forms.• Plants utilize soluble sulfate-S.• Sulfate-S can leach from topsoil.• Many Virginia soils have good
subsoil sulfate-S reserves.• S deficiency most common in
seedling stage, sandy soils.• Gypsum, sul-po-mag,
magnesium sulfate, and elemental sulfur supply S.
Deficiency: youngest leaves turn evenly yellow.
Micronutrients essential for plant growth
• Zinc (Zn)• Copper (Cu)• Manganese (Mn)• Iron (Fe)• Boron (B)• Molybdenum (Mb)• Nickel (Ni)• Chorine (Cl)• Sodium (Na)
Fe deficiency: youngest leaves yellow between veins.Mn, Cu, Zn deficiencies similar.
Amending micronutrients• Boron (B) deficiency is
common in Virginia.• Zn, Cu, Mn are occasionally
deficient.• Poultry litter is Zn and Cu
source.• Molybdenum occasionally
deficient in legumes.• NOP allowed micronutrient
supplements are available.
Acute B deficiency:distorted or damagedgrowing points.
