Using Cover Crop Mulches for Weed Control in Organic and Conventional Cotton Production.

Cover crop mulches can be used for weed suppression by organic producers to alleviate dependency on tillage and can be used to reduce herbicide-resistant weed pressure for conventional producers. The objective of this experiment was to evaluate the management of a cereal rye/crimson clover cover crop mulch and the effects on soil moisture, soil temperature, cotton emergence, weed suppression, and cotton lint yield in organic and conventional weed control scenarios. The experiment was conducted in Lewiston, NC from 2014-2015 and in Clayton, Rocky Mount, and Lewiston, NC from 2015-2016. A cereal rye/crimson clover cover crop mixture was planted in mid-October using a grain drill and was terminated one-week prior to cotton planting using a roller-crimper or herbicide application. Cotton was planted directly into the cover crop mulch. Main plot treatments included no cover crop, planting into standing cover crop, planting into roll-killed cover crop moved several inches from the cotton row, planting into fertilized then roll-killed cover crop moved several inches from the cotton row, and planting into roll-killed cover crop with minimal residue movement from the cotton row. Subplot treatments included organic and conventional weed control scenarios. Without fertilizing the cover crop, cover crop biomass ranged from 3,817-6,612 kg ha^-1 across our environments. Fertilizing the cover crop in early March with 34 kg N ha^-1 provided an additional 774 kg ha^-1 in cover crop biomass on average across our environments. Cotton emergence was reduced by standing cover crop residue and when the cover crop was moved minimally from the cotton row at planting. Soil temperature was reduced by the presence of cover crops but soil moisture availability was enhanced by the presence of cover crops throughout the growing season. Excellent weed control was achieved when the cover crop mulch was combined with herbicide use. When herbicides were not used, the cover crop biomass levels achieved did not provide adequate weed suppression to allow for respectable cotton lint yield in 2015. Large reductions in lint yield were observed when herbicides were not used regardless of cover crop management strategy.