Influence of Cover Crop Mixtures on Soil Health and Weed Control in Cotton Production Systems

Abstract

The restoration of soil health is a crucial step in maximizing productivity in the historically-eroded Ultisols of the Southeast. The utilization of winter cover crops can potentially improve soil health by increasing soil organic matter, improving soil structure, and enhancing nutrient-use efficiency. Studies were established at the Tennessee Valley Research and Extension Center (TVREC) and Wiregrass Research and Extension Center (WREC) to examine the impact of cover crop monocultures and mixtures on dynamic soil health indicators in cotton (Gossypium hirsutum) production systems. Eight treatments including monocultures and combinations of cereal rye (Secale cereale), crimson clover (Trifolium incarnatum), and Daikon radish (Raphanus sativus) were arranged in a randomized complete block design with winter fallow controls. Cover crop biomass was collected at termination, and soil samples were collected two weeks following termination. Measured soil health indicators included permanganate oxidizable carbon (POXC), total carbon (TC), water stable aggregates (WSA), and soil strength (AUCC.I.). Stratification of TC with depth occurred at TVREC, and TC under crimson clover, rye-clover, and rye-radish was higher than TC under the winter fallow control. In both 2018 and 2019, POXC at TVREC was not different between treatments at the 0-5 cm and 5-10 cm depths, while POXC was higher under crimson clover compared to the rye-crimson clover mixture at 10-15 cm. There were no differences in TC and POXC between treatments at WREC, but POXC was higher in 2019 than in 2018. WSA values from both locations were not different between treatments within the same depth class in both 2018 and 2019. No differences in AUCC.I. occurred between treatments at TVREC, while the rye monoculture was less compacted than the crimson clover monoculture and 3 crimson clover/radish mixture at WREC. Additional years under these cover crop treatments may be required to detect changes in soil health. Winter cover crops are also a common tool for integrated weed management in both conventional and conservation agricultural systems. Two trials were established at E.V. Smith Research Center in Shorter, AL in November 2016 to evaluate the efficacy of several cover crop systems as a supplemental form of weed control in cotton production systems. The first trial consisted of twelve treatments. Cover crops included a rye monoculture, a mixture of rye, oats (Avena sativa), wheat (Triticum aestivum), crimson clover, and Daikon radish, and winter fallow. Each cover crop system was evaluated under four herbicide regimes including PRE only (pendimethalin and fomesafen), POST only (dicamba fb glyphosate), PRE+POST, and herbicide-free. Amaranthus control was lower in all herbicide-free treatments compared to all PRE+POST, and cotton lint yield was lower in the herbicide-free treatments compared to treatments with herbicide applications. Lint yield was higher in PRE+POST treatments compared to herbicide-free treatments, regardless of cover crop. Lint yield under PRE only treatments were not different from PRE+POST while POST only treatments had lower lint yield than PRE+POST treatments in 2018. The second trial includes rye monocultures as whole-plot and row-middle only treatments, a clover-radish mixture in the whole plot and within the cotton row only, and three-species mixtures as whole-plot treatments and with precision placements; all treatments managed with a PRE+POST herbicide regime. In the cover crop placement trial, weed control was often similar between treatments in the same year, and cotton yield was only influenced by year. Results indicate that cover crops alone will not eliminate the need for chemical weed control.