Long-Term Crop Response to Conservation Tillage

In 1987, the United States Department of Agriculture (USDA-ARS) National Sedimentation Laboratory, in cooper­ ation with the Mississippi Agricultural and Forestry Experi­ ment Station (MAFES) and the Natural Resources Conservation Service (NRCS), initiated an interdisciplinary research project to develop profitable and environmentally sustainable conservation production systems for silty upland areas of the Midsouth. Results from the first 5 years of this project were reported to the SCTC in 1993. Culture details and soil types are listed in the earlier paper (Dabney et al., 1993).Treatments includ­ ed no-tillage, conventional (chisel, disk, cultivate), ridge, and minimum tillage for cotton, grain sorghum, and soybeans. A wheat-soybean and grain sorghum-wheat-soybean doublecrop (three crops in 2 years) systems were also includ­ ed. No-tillage cotton followed wheat cover and no-tillage sor­ ghum followed vetch cover. In this phase, both no-tillage cotton and grain sorghum yields improved with time relative to conventional tillage, while crop yields with minimum and ridge-tillage were similar to those with conventional tillage. We reported earlier that soil loss from runoff plots with no-tillage was in the range of 1to 2 tons/acre/year, sufficient for conservationcompliance. An economic analysis of cropping systems showed the doublecrop wheat-soybean system to be the most profitable, no-tillage cotton was profitable, and all continuousgrain sorghum systemswere unprofitable (Dab­ ney et al., 1993). After the fifth crop year, the study was revised. No-tillage replaced minimum and ridge tillage, corn replaced grain sor­ ghum, and full-season no-tillage soybeans and a corn-cotton rotation were initiated (Table 1). The first-phase conventional and no-tillage were retained. New no-tillage corn and cotton were with and without cover crops. The new design permits evaluation of the: (1) time in no-tillage (tillage history), (2) cover crops within no-tillage systems, and (3) crop rotation. Objectives of this revised study were: (1) to monitor longterm crop responses to conventional and no-tillage, (2) to evaluate crop responses when changing to an untilled environ­ ment, and (3) determine the effect of crop rotation on crop