Cover Crops Provide Much More than Just Cover


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This presentation was the Keynote address for the Innovative Farmers of Ontario (Canada) in February 2014. Some slides may not work as well as intended without their animations.

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  • Roots go deeper than you might think.
  • kg/ha almost equal to lbs/acre (x 0.9)… Mineralization appears tied to increase in spring temperatures- doesn’t have to get HOT, but just when air is warming, N from radish is mineralized. This was a field with high N capture (150-200 kg N) in fall. Nitrate-N was lower in fields with less N capture in fall. This was for no-till- tillage did increase nitrate further for all cover crop treatments.
  • Scene shows Giddings hydraulic probe getting deep soil cores.
  • Cover Crops Provide Much More than Just Cover

    1. 1. More Than Just Cover Cover Crops as Multipurpose Tools for Soil Quality Ray Weil Professor of Soil Science
    2. 2. “Cover crop”, “Green manure”, “Catch crop” In factcall them, thesecrops,grown for using cover crops • Whatever you changes everything! the soil can do a lot more than just prevent erosion. Resource efficiency Biological diversity Soil quality
    3. 3. Harvest Planting Cover crops can utilize otherwise wasted resources The sun shines, the rain falls and microbes work 12 months a year, but this typical mid-west grain farm captures only 3-4 months of this activity.
    4. 4. Cover Crops Liberate Farmers from Market Dictates on What to Plant 1. Cool season grasses 2. Cool season Legumes 3. Cool season Brassicas 4. Warm season grasses 5. Warm season legumes 6. Warm season broadleaves
    5. 5. Cover crops change everything! Cover crops Labile C Soil organic matter Increased infiltration Soil Cover Soil temperature Rhizobial associations Mycorrhizal associations Nutrient capture (N, P, S, K, etc) Reduced erosion loss Soil Aggregation Reduced evaporation Weed suppression Food web activity Bio-drilling Enhanced crop growth Soil water Nematodes P- fertility Reduced leaching loss (N) Nitrogen fertility
    6. 6.  Plan your cover crop as carefully as your cash crops.  What do you want a cover crop to do?  What is your niche and growing window? Alternate drill rows of rye and radish After trying single cover crops, you may want to try simple mixtures. Pure radish Alternate drill rows of Sudex and radish
    7. 7. Farmers are good at figuring out ways to extend their cover crop planting window!
    8. 8. Even a simple rye cover crop can make a measurable difference to your soil Cover Crop Treatment Crop or Soil Parameter No Rye Rye Soybean plant, kg ha-1 5275.5 ** 5995.1 Soybean yield, kg ha-1 2704.8 * 3054.9 Active C mg kg-1 624.2 ** 661.7 C respired in 2 days, mg kg-1 213.1 ** 255.0 Total organic C g kg-1 17.90 ns 19.06 Mineralizable N mg kg-1 82.01 ** 101.81 Stable aggregates % 60.40 ** 69.40 Overall Means of 6 sites in MD and PA with 2 to 6 years of rye cover crop in corn – soybean rotation.
    9. 9. A single rape or rye cover crop changed the soil food web from bacterial to fungal-dominated. Data taken 8 months after cover crops were Fungal-feeding killed. Coslenchus sp. nematode Gruver, Weil, Zasada, Sardanelli, and Momen 2010 (J. of Applied Ecology).
    10. 10. Earthworms and cover crops work together.
    11. 11. Key differences are in the roots!
    12. 12. Harvested part (grain, fruit, leaves) Shoot residues Animal feed Fuel Roots Rhizo-deposition CO2 Soil organic carbon SOC 100 kg C as leaves  ~ 15 kg SOC 1 year after incorporation. 100 kg C as roots  ~ 30 kg SOC 1 year after incorporation.
    13. 13. Soil C content 0 Soil Depth, m > 90% of the data is here. 1 Leaching and re-adsorption of dissolved organic carbon DOC 2 Roots and rhizodeposition Much more effort is needed to study deep soil C > 60% of the carbon is here. SOC in deep layers tends to have low C/N and slow turnover times.
    14. 14. Researchers are no longer so sure that no-till increases total profile organic carbon. Depth distribution of corn roots Amount of of C measurements Distribution soil carbon soil No-till Plowed But very few of the tillage comparison included cover crops! Root system of a corn plant (field excavation by Weaver 1929) and the sampling depths used in 140 comparative studies of tillage impacts on soil carbon. Scale in feet. Baker, J.M., T.E. Ochsner, R.T. Venterea, and T.J. Griffis. 2007. Tillage and soil carbon sequestration--what do we really know? Agriculture, Ecosystems & Environment 118:1-5.
    15. 15. Cover crop roots build soil bio-physical quality
    16. 16. A little extra organic matter goes a long way to stabilize aggregates and keep soil surface open. 1.2% OM 2.0% OM
    17. 17. Cover crops can improve structure deeper in the soil More on biodrilling to fight compaction in the break out session tomorrow!
    18. 18. Cover crop surface residues influence: • Soil temperature • Soil moisture • Weed pressure Forage radish residues Spring oat residues
    19. 19. Four stages of a unique cover crop 19
    20. 20. Vegetation and residues dramatically suppress weeds and influence no-till seedbed conditions. Rye Forage Radish
    21. 21. Forage radish “film” during rapid decomposition
    22. 22. Effect of living rye v decayed forage radish on soil temperature at 5 cm depth in April in Md. (oC) 25 20 15 10 5
    23. 23. Effect of living rye v decayed forage radish on soil water at 5 cm depth in April in Md.
    24. 24. Soil moisture at 5 cm after cover crop treatments, Clarksville Md 2013 Workable days (below 80% plastic limit)
    25. 25. Zoned cover crop mixtures
    26. 26. Like deep ripping and using a burn down herbicide in the planting row while mulching the inter-row Radish planted on 75cm (30”) centers with 3 rows of oats drilled in between. September Joel Gruver, Western Illinois Univ. 26 photo by Joel Gruver, UWI
    27. 27. Another major cover crop function: enhanced nutrient management Reduce losses Enhance availability Add nitrogen Recover deep nutrients
    28. 28. Why use cover crops to manage nutrient loss? The environment • Nutrient leaching (N) • Runoff/erosion (P) Farm profitability Source Price / kg N Price / kg P Urea Lake Erie $1.40 DAP $1.40 Legumes Dairy manure $2.75 Cost of seed, land, labor, lost crop ? ?
    29. 29. Very complex as N occurs in •Solids •Liquids •Gases Blue = anaerobic processes Bright green = N addition to soil Dark olive = N losses to water The N Cycle From Weil and Brady 2015 The Nature and Properties of Soils.
    30. 30. Inputs of N to soil organic matter as plant and animal residues .
    31. 31. Decomposition of residues and release of N by mineralization. SOM R-NH2 Decomposition promoted by: • Good aeration • Warm temperature • Easy to digest carbon • Tillage NH4+
    32. 32. Grass turns greener because Fairy ring fungi release N from SOM
    33. 33. Oxidation N from soil Conversion ofof Ammonium to Nitrate organic matter to soluble mineral forms. Organic matter Soil organisms NO3- Nitrate NH4+ NO2nitrite Leaching loss Ammonium Nitrification needs: •Oxygen (aeration) •Warm temperature •Presence of nitrifiers
    34. 34. In a soil with 2.5% organic matter, the top 30cm has: ~4000 kg/ha ORGANIC Nitrogen < 100 kg/ha Inorganic N/year • nitrate-N • ammonium-N • other forms (gases etc.)
    35. 35. Crop use of N and P Crop Yield N P Canola 3000 kg seed 119 19 Corn 9000 kg grain 133 25 Soybean 3100 kg grain 199 20 Wheat 3700 kg grain 69 13 To estimate N_P_K in harvest, use tool at
    36. 36. Nutrient capture: nitrogen in fall
    37. 37. Soil v Cover Crop or Weed Nitrogen Contents in November 12080 = 40  150 kg N taken up by the cover crop  40 kg N missing from the upper 1 m of soil  Where did the other 110 kg N come from?  From deeper soil layers? 150 kg N taken up by plants Data: Wang and Weil, unpublished
    38. 38. Nitrate-N in 180 cm soil No cover: 173 kg/ha Forage radish: 48 kg/ha Oilseed radish: 62 kg/ha Last spring’s fertilizer 2 years ago fertilizer Loamy sand, Beltsville, Maryland After corn-wheat Dean, J.E., and R.R. Weil. 2009. Journal of Environmental Quality 38:520-528.
    39. 39. A few weeks later planting reduces weed suppression and biodrilling but not nitrogen capture. Effect of seeding date on forage radish growth & nitrogen uptake in fall Effect of seeding date on forage radish dry matter and N uptake. Means of 3 locations in 2007. 4.625 Shoot dry matter 5250 4625 4000 3375 2750 Shoot tissue N, % Shoot DM, kg/ha 5875 250 5.000 Tissue N conc. 4.250 3.875 3.500 3.125 2.750 225 Shoot N Uptake, kg/ha 6500 Shoot N uptake 200 175 150 125 100 2125 2.375 75 1500 2.000 50 1 2 3 4 5 Seeding date, weeks after Aug. 20 1 2 3 4 5 Seeding date, weeks after Aug. 20 1 2 3 4 5 Seeding date, weeks after Aug. 20 Means of 3 sites
    40. 40. Nitrogen Capture by October-Planted need to get Timing is everything! – We Rye Cover Crop Topsoil N tied cover crops planted earlier!up by rye 2 10 15 50 Large amounts of N lost September October November March April
    41. 41. Nitrogen Capture by Early of early planting and Some advantagesSept-Planted Radish Cover Crop frost killing. N available to early 25 September 125 200 October November ? N ? planted cash crop March April
    42. 42. Nutrient capture: nitrogen in spring Soil May 10th
    43. 43. Soil Nitrate (0-20 cm) Nitrate-N 33 (kg ha-1) increase from radish Nitrate-N 34 (kg ha-1) increase from radish N mineralization in spring Lounsbury and Weil 2013
    44. 44. Maize Response to Early Spring Nitrogen Release by Radish Cover Crop Following radish Following rye
    45. 45. Increased available phosphorus in surface soil horizons Silt loam, upper 120 cm In 3rd winter of cover crop trts. 0 lsd 0.05 25 lsd 0.05 Cover crops can enhance topsoil fertility with more than just nitrogen Soil depth lsd 0.05 50 ns ns 75 ns ns 100 ns 125 0 No cover Forage radish Oilseed Radish Rapeseed Cereal rye 20 40 60 80 100 120 Soil test P (Mehlich 3), mg/kg •Deep P brought to surface & bound P made available 140
    46. 46. P Concentration around radish holes White and Weil (2009)
    47. 47. Sulfate in Topsoil (0-20 cm) Clarksville Wye Lounsbury and Weil 2013
    48. 48. Brassicas are exceptionally high in certain nutrients: calcium, phosphorus, sulfur , boron Calcium contents Phosphorus contents
    49. 49. Deep Soil Nutrients: Neglected Resource under your feet?
    50. 50. Some Nutrient Capture Questions Needing Research 1. How big is the deep N pool in early fall ? 2. How does aerial seeding in Aug compare to drilling in Oct? 3. Can irrigation or seed coating ensure early stands with aerial seeding? 4. Can on‐the‐spot nitrate‐N tests predict need for covercrop starter N? 5. Can ~15 lbs starter N allow covercrops to capture 100 lbs of extra N? 6. Can cash crops use the captured N (+P, K, S) in spring?
    51. 51. Think about… Managing plants to soils improve plants soils Questions?