COVER CROPS, TILLAGE, AND GLYPHOSATE EFFECTS ON CHEMICAL AND BIOLOGICAL PROPERTIES OF A LOWER MISSISSIPPI DELTA SOIL AND SOYBEAN YIELD.

The adoption of sustainable cropping systems, including cover crops and no-tillage practices can promote soil conservation and improve soil quality. However, the selection of the best management practices to increase crop production is needed. A field study was conducted from 2001 to 2005 at Stoneville, MS, on a Dundee silt loam soil to assess the effects of cover crop (rye [Secale cereale L.], hairy vetch [Vicia villosa Roth], or none), tillage [conventional tillage (CT) or no-tillage (NT)] and herbicide (glyphosate or non-glyphosate post emergence), on soil chemical properties, soil microbial ecology, and soybean yield. Cover crops were killed before soybean (Glycine max L. Merr.) planting, incorporated into CT soils, and left on surface in NT soils. Soil (0 to 5 cm depth) was sampled at planting, and mid season following soybean planting. Soil was analyzed for total organic carbon (TOC), total nitrogen content (TNC), nitrate, electrical conductivity, and soil moisture. Biological parameters included fluorescein diacetate (FDA) hydrolysis, total bacteria, gram-negative bacteria and total fungi propagules, and microbial community analysis based on total fatty acid methyl ester (FAME) analysis. The greatest accumulation of TOC and TNC was under NT, particularly under cover crop management. NT soils, especially under cover crop management maintained the highest soil moisture content. Soils managed under a hairy vetch cover crop maintained at least two-fold greater soil nitrate and electrical conductivity compared to no cover crop regardless of tillage. FDA hydrolysis was 55 to 120% greater under NT compared to CT with the highest activity associated with cover crop managed soils. Patterns of microbial community structure were dependent on year and sample time dependent with a greater effect of tillage compared to cover crop. Soybean yields were consistently similar under CT and NT systems. Despite the beneficial effects on soil properties, soybeans grown with rye cover crop, regardless of CT or NT system, consistently yielded lower compared to hairy vetch or no cover crop. Adoption of cover crop-based systems by soybean farmers is less likely due to additional costs. Alternatively, soybean farmers are more likely to adopt NT-based production systems to potentially increase soybean yield and improve soil quality. [ABSTRACT FROM AUTHOR]