MOISTURE MANAGEMENT & IRRIGATION WITH COVER CROPS

Transcription

1 MOISTURE MANAGEMENT & IRRIGATION WITH COVER CROPS 1 Michele L. Reba, PhD, PE Research Hydrologist USDA-ARS Jonesboro Worksite National Sedimentation Laboratory michele.reba@ars.usda.gov

2 ORGANIZATION Introduction: why cover crops? Concepts and Terms Hydrologic Cycle Soil Management Water Management Cover Crop Management Cover Crop Selection Cover Crop Resources

3 WINTER RYE COVER CROP REDUCED RUNOFF THROUGHOUT YEAR AVERAGE OF 10 YEARS AND IN THREE VEGETABLE CROP SYSTEMS FREEHOLD LOAMY SAND, 3% SLOPE, NEW JERSEY Brill and Neal Agron. J. 42: No cover Rye cover

4 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 Trans. ASAE 42:

5 WEED SUPPRESSION IN NO-TILL CORN BY SUB CLOVER (BACKGROUND IS CONVENTIONAL TILLAGE, NO COVER)

6 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

7 CONCEPTS 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

8 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.

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10 HYDROLOGIC CYCLE & COVER CROPS Precipitation Trapping Snow Evaporation Runoff Altering radiation (change albedo: spring warming, reduce depth to soil freeze/delay soil thaw) wind speed, vapor pressure deficit & surface temperature Increasing hydraulic roughness, canopy & surface detention storage, infiltration rate Soil profile storage capacity Increasing ET & modify porosity Macropore geometry: root growth & macrofauna activity Decreasing leaching losses Increasing transpiration & scavenging nutrients

11 WINTER RYE COVER CROP REDUCED RUNOFF THROUGHOUT YEAR AVERAGE OF 10 YEARS AND IN THREE VEGETABLE CROP SYSTEMS FREEHOLD LOAMY SAND, 3% SLOPE, NEW JERSEY Brill and Neal Agron. J. 42: No cover Rye cover

12 Cover crop residue mulch increases soil temperature Dabney, Delgado, and Reeves Comm. in Soil Sci. and Plant Anal. 32:

13 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)

14 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.

15 PERCENT KILL OF SUMMER COVER CROPS IN NORTH CAROLINA (CREAMER AND DABNEY, 2002, AM J. ALT. AG. 17:32-40) Cover crop Growth stage Mow Undercut Roll (smooth) Cowpea Vegetative Soybean Early bloom Buckwheat Mature Pearl Millet Heading German Millet Green Seed Sorghumsudangrass Mature

16 COVER CROP SELECTIONS FOR THE MID-SOUTH (HUMID ZONES 6+) Winter Hairy Vetch (Vicia villosa) Balansa clover Rye Oat (Trifolium michelianum) Paradana or Frontier (Secale cereal) Abruzzi or Merced (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)

17 Let cover crops grow longer (if water is available) increased residue can be managed Increased residues control weeds increased residue conserves water later maintains mycorrhiza hyphae network for early growth boost Do not till needlessly it is like taking money out of the bank!

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 RODALE ROLLER AT DCDC, METCALF, MS, IN 2006 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

20 CONCLUSIONS: COVER CROP OPPORTUNITIES Catch crop or green manure Reduce runoff Surface temperature Porosity Synchrony Biomass production from available water and sunlight

21 SELECTED RESOURCES ON THE WEB ATTRA NAL/SAN ARS California Michigan Cedar Meadow (Steve Groff) Rolf Derpsch

22 THANK YOU Michele L. Reba, PhD, PE Research Hydrologist USDA-ARS-Jonesboro, AR National Sedimentation Laboratory 22