Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2003
Publication Date: 11/1/2003
Citation: Reddy, K.N., Zablotowicz, R.M., Locke, M.A., Koger, C.H. 2003. Cover crop, tillage, and herbicide effects on weeds, soil properties, microbial populations, and soybean yield. Weed Science.51:987-994. Interpretive Summary: Information on effects of cover crops and no-tillage on weeds, soil resources and soybean production is needed to implement conservation management strategies for the Mississippi Delta. Scientists at the Southern Weed Science Research Unit in Stoneville, Mississippi completed a four-year study evaluating various herbicide, tillage (conventional or none) and cover crop (rye or crimson clover) systems in soybean. Both cover crops have potential for improving soil quality and reducing weed density in soybean; however, optimum weed control was obtained when herbicides were included. Rye offered better weed suppression than crimson clover, while crimson clover treatments increased soil nitrate and had the greatest increase in soil organic matter. Soybean yields were equivalent in no cover crop and rye, while they were lower in crimson clover compared to no cover. Soybean yield and weed density were similar for both tillage systems; however, no-tillage enhanced microbial activity, organic carbon, and availability of some nutrients in soil. These findings demonstrate that no-tillage is a practical and profitable option for soybean farmers who desire practices with lower inputs and also provide environmental benefits.
Technical Abstract: A field study was conducted during 1997-2001 on a Dundee silt loam soil at Stoneville, MS to examine effects of rye and crimson clover residues on weeds, soil properties, soil microbial populations, and soybean yield under conventional tillage (CT) and no-tillage (NT) systems with preemergence (PRE) only, postemergence (POST) only, and PRE + POST herbicide programs. Rye and crimson clover were planted in October, desiccated in April, and tilled (CT plots only) before planting soybean. Both cover crop residues reduced density of barnyardgrass, broadleaf signalgrass, browntop millet, entireleaf morningglory, and hyssop spurge, but did not affect yellow nutsedge at 7 wk after soybean planting (WAP) in the absence of herbicides. Densities of these weed species were generally lower with PRE-only, POST-only, and PRE + POST applications compared with the no herbicides. Total weed dry biomass was lower with CT (1570 kg ha-1) vs NT (1970 kg ha-1), rye (1520 kg ha-1) vs crimson clover (2050 kg ha-1), and PRE + POST (640 kg ha-1) vs PRE-only (1870 kg ha-1) or POST-only (1130 kg ha-1) treatments at 7 WAP. Soils with crimson clover had higher organic matter, NO3-N, SO4-S, and manganese, and lower pH compared with rye and no-cover crop soils. Total fungi and bacterial populations, and fluorescein diacetate hydrolytic activity were higher in soil with crimson clover, followed by rye and no-cover crop. Soybean yields were similar between CT (1830 kg ha-1) vs NT (1960 kg ha-1), no-cover crop (2010 kg ha-1) vs rye (1900 kg ha-1), and rye vs crimson clover (1790 kg ha-1), but higher in PRE + POST (2260 kg ha-1) vs PRE-only (1890 kg ha-1) or POST-only (1970 kg ha-1) treatments.