Cover crops and soil health. Erin Silva, Organic Production Specialist University of Wisconsin, Dept. of Plant Pathology

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1 Cover crops and soil health Erin Silva, Organic Production Specialist University of Wisconsin, Dept. of Plant Pathology

2 Purposes of cover crops Reduce erosion from water and wind Increase soil organic matter and soil biological activity Provide biological nitrogen fixation Capture and recycle or redistribute nutrients Improve soil physical conditions (aggregation, compaction, moisture mgmt.) Source of forage and feed Weed suppression and biodiversity enhancement

3 Purposes of cover crops Reduce erosion from water and wind Increase soil organic matter and soil biological activity Provide biological nitrogen fixation Capture and recycle or redistribute nutrients Improve soil physical conditions (aggregation, compaction, moisture mgmt.) Source of forage and feed Weed suppression and biodiversity enhancement

4 How do cover crops contribute to fertility? Green manure crop cover crop or forage grown to incorporate into soil while green or flowering, to improve soil SOM Catch crop or trap crop cover crops planted to reduce nutrient leaching following a main crop Cover crops do not create nutrients in soil, but can recycle and release Legumes fix nitrogen

5 How much of a benefit are cover crops to soil fertility? Legumes biological N fixation How much N fixed? and released? and when? Non-legumes How much N trapped? and released? and when?

6 Two good nitrogen/cover crop resources Estimating plant-available nitrogen release from cover crops - PANFromCoverCrops.pdf nces_in_nitrogen_management_for_water_quali ty/anm9_a41356aad3b6a.pdf

7 Species Characteristics: Nitrogen Contribution Grasses and brassicas only acquire N from the soil Legumes can acquire N from the atmosphere through N fixation Over time cover crops and forages (as green manure crops) add to the organic matter content of the soil and build nutrient content Less nutrient and organic matter increase if cover crops and forages are harvested Forage Radish Cereal Rye Austrian Winter Pea Nodules LaChance et al., courtesy of Murrell

8 Cover crops and nutrient sequestration Trap nutrients that would otherwise leak out during fallow periods leaching through soil losses as eroded soil or runoff Release nutrients later ideally at the time needed by the next crop

9 Trap crops Cereal rye, annual ryegrass, wheat, barley, sorghum sudan, pearl millet Age/stage of plant when killed, determines N% and C:N ratio, and therefore decomposition rate

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11 Legume Green Manure Crops Produce lbs. N/acre Species Amount of growth/biomass produced %N in plant Approx % of N available to subsequent crop Incorporation of green manure increases N for 4-6 weeks Later N applications needed?

12 Average biomass yields and nitrogen yields of several legumes Cover Crop Biomass Nitrogen Tons/acre lbs./acre Sweet clover Berseem clover Crimson clover Hairy vetch ATTRA, 2003

13 Distribution of plant nitrogen in legume tops and roots Crop Tops Roots %N %N Soybeans 93 7 Vetch Cowpeas Red clover Alfalfa ATTRA, 2003

14 Residue Addition and N Availability High carbon residues added Avail. Soil N Time Immobilization (tie-up) Mineralization (release of N)

15 Residue Addition and N Availability Low carbon residues added Avail. Soil N Time No Immobilization (tie-up) Mineralization (release of N)

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18 Sullivan and Andrews, 2012

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20 Estimating Plant Available N

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24 Which cover crops should I choose? Where is it fitting into your rotation? Planting window Interaction with subsequent crops insects, diseases What functions do you want to fulfill? What tools do I have to manage them?

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