COVER CROPS FOR NEW AMERICAN CROPPING SYSTEMS

1. COVER CROPS FOR NEW AMERICAN CROPPING SYSTEMS Seth Dabney USDA-ARS National Sedimentation Laboratoryseth.dabney@ars.usda.gov

2. Organization • Introduction: why cover crops (and no-till)? • Concepts and Terms • Cover Crop Management (killing cover crops) • Cover Crop Selection • Cover Crop Resources

3. Why Grow Cover Crops? • Soil Management • Water Management • Pest Management • Nutrient Management

4. Winter rye cover crop reduced runoff throughout yearaverage of 10 years and in three vegetable crop systemsFreehold loamy sand, 3% slope, New Jersey No cover Brill and Neal. 1950. Agron. J. 42:192-195. Rye cover

5. Cover crops, high-residue crops, and no-till management can reduce runoff (and erosion even more!)average of 6 years, Grenada silt loam, 5% slope, Mississippi Reduced winter runoff with cover crops is mainly due to increased transpiration (and biomass production). Meyer et al. 1999. Trans. ASAE 42:1645-1652.

6. Insufficient Residue = Soil Crusts(no-till won’t work with bare soil)

7. Sprinkler-irrigated rice on Crowley silt loam Conventional-till No Cover Crop No-till No Cover Crop Sprinkler Irrigation trigger No-till Cover Crop Dabney (1998) J. Soil and Water Cons. 53(3):207-213 Cover crop residue mulch increases infiltration

8. Why Grow Cover Crops? • Soil Management • Water Management • Pest Management • Nutrient Management

9. Weed suppression in no-till corn by sub clover (background is conventional tillage, no cover)

10. Stripped cover crops of rye and a clover mix in Georgia for beneficial insect habitat. Cotton was planted into the killed strips of rye while the clover was left growing until an application of Roundup at the 4 to 6 leaf stage Photo: Harry Schomberg

11. Why Grow Cover Crops? • Soil Management • Water Management • Pest Management • Nutrient Management

12. N managementconcepts and terms • green manure: cover crops grown mainly to improve the nutrition of subsequent main crops; may contain legumes that can add N to the cropping system • catch crop: cover crops grown to catch available N in the soil and thereby prevent leaching losses of N already in a cropping system • pre-emptive competition: uptake of soil nitrate by cover crops that would not have been lost to subsequent crops by leaching, thereby reducing availability of N to the subsequent crop

13. Concepts and terms • To be most effective, green manure crops should winter kill, be grazed, or be killed early in the spring to prevent pre-emptive competition and so that green manure N can be rapidly mineralized. • To be most effective, catch crops should be planted early in the fall to maximize root growth and N uptake. • High residue cover crops can increase yield potential and build soil C, but may also increase the economically optimal fertilizer N rate.

14. Catch crop effectiveness is highly correlated with rooting depth, but not with root densityWith warm weather, broad leaf plants may root more deeply more quickly than grasses Thorup-Kristensen, K. 2001. Plant and Soil 230: 185–195.

15. Synchrony – temporal match between N supply and demand (Crews and Peoples. 2005. Nutrient Cycling in Agroecosystems 72:101-120.)

16. Source: Dabney et al. 1989. Agron J. 81:483-487 Rice and legume cover crops:no-till improves synchrony

17. In reseeding legume systems, seed may contain ~ 50 kg N/ha Reseeding crimson clover biomass and N accumulation in GA Sampling (of above ground biomass, litter, or roots) indicates net growth, not gross biomass production or N uptake Harper et al. 1995. Crop Sci. 35:176-182.

18. Plowing cover crops into soil does not increase soil organic matter • Tillage controls weeds, loosens soil, and smoothes fields • burns up soil organic matter • speeds organic N mineralization and nitrification • Cover crops make no-till more successful • (make no-till vegetables possible) • No-till with cover crops increases soil C

19. Worried about ammonia loss from no-till residues?

20. Even when hay is rained on, total NH3 losses to the atmosphere are minor

21. No-till with cover crops wheat cover

22. Cover crop residue mulch increases soil temperature Dabney, Delgado, and Reeves. 1991. Comm. in Soil Sci. and Plant Anal. 32:1221-1250.

23. Improved early season cotton growth and survival with no-till mycorrhiza hyphal counts per mm2

24. Why Not Grow Cover Crops? • Time • Cost • Lack of water • Stand problems • Seed placement • Pest and disease risks

25. 10 ton biomass yield in California~50 mm (2 inches) of water per ton of cover crop biomass Photo: Jeff Mitchell; Rolling rye cover crop, T & D Willey Farms, Madera, CA, April 21, 2006

26. Rhizoctonia infection of sorghum seedlings grown in soil with and without cover crop residues Dabney, Schrieber, Rothrock and Johnson. 1996. Agron. J. 88(6):961-970.

27. No-till planter: coulter to cut residues; double-disk opener set slightly deeper to plant into firm soil

28. Enhanced no-till planter: Tined-wheel row cleaner, scalloped double-disk openers reduce “hair-pinning” and tined press wheels close no-till seed slot without compaction.

29. Row cleaners can clear heavy residues,improving stands of direct seeded crops

30. Cover Crop Management(Killing Cover Crops without Tillage) • Spray (works best early) • Mechanical (works best late) • Mow (flail gives most uniform residue distribution) • Undercut • Roll (roll chop, knife roll)

31. Mowing – flail mowers leave residues evenly distributed, but operation and maintenance costs are high.

32. Undercutter (Nancy Creamer, NC State)

33. South AmericanKnife-rollers

34. American Rollers, Roll-choppers,and Roll crimpers

35. GA farmer, Lamar Black, rolls a 2 meter tall rye cover crop prior to planting corn or cotton The resulting mulch suppresses weeds, conserves water, and lowers peak soil temperature.

36. Cover Crop Management (killing cover crops) Direct seed no-till pumpkin into rye cover crop in Southwest VA (Ron Morse)

37. No-till transplanting cabbage into rolled rye, Hillsville, VA (Ron Morse)

38. Percent kill of summer cover crops in North Carolina (Creamer and Dabney, 2002, Am J. Alt. Ag. 17:32-40)

39. German or Foxtail Millet(Setaria italica) Mowed or Rolled doesn’t re-grow

40. No-till no-herbicide broccoli transplanted into rolled foxtail millet (Ron Morse) Weed control lasts longer after rolling than after mowing.

41. Sunn Hemp – Crotalaria juncea rapid legume growth following corn in Alabamakilled by frost ($2.5/lb from http://desertsunmarketing.com/)

42. Sunflowers grow fast, has wildlife benefits, and can be killed by rolling; mulch degrades quickly

43. Winter Hairy Vetch (Vicia villosa) Balansa clover (Trifolium michelianum) ‘Paradana’ or ‘Frontier’ Rye (Secale cereal) ‘Abruzzi’ or ‘Merced’ Oat (Avena sativa) Summer Cowpea (Vigna unguiculata) Sunn hemp (Crotalaria juncea) Foxtail millet (Setaria italica) Sunflower (Helianthus annus) Forage turnip (Brassica rapa) Forage radish (Raphanus sativus) Cover Crop Selections for the mid-South (humid zones 6+)

45. Balansa cloverTrifolium michelianum Savi– a superior reseeding winter cover crop Mississippi County, AR 7A Moorhead, MS 8A Tiptonville, TN 6B

46. On-farm reseeding demonstration/adoption Thighman Lake

47. Seed size: 1000 to 1400 per gram Plant 5 lb/a (8 if coated); ~$2.00/lb Kamprath Seed (800-466-9959), Manteca, CA

48. Rye, Balansa, or No cover(Average of NT and RT) silty clay soil, Stoneville, MS N Fertilizer Applied Locke et al. (unpublished) NT with rye was most profitable over four years

49. Sweet Potato

50. Rodale Roller at DCDC, Metcalf, MS, in 2006part of a Conservation Innovation Grant Things that went wrong: Rye Stand Marginal (Rita) Rye too old (roller delivered late) Soil too dry Planter depth set too shallow (poor cotton stand) Needed herbicide (thin mulch, poor stand), but herbicide was caught on mulch (poor weed control) Fertilizer N not increased (pre-emptive competition) Result: poor stand, poor growth, poor weed control, poor yield