Management of cover crops and soil amendments affect yield outcomes during organic transition

Abstract

This study sought to assess the impact of cover cropping and high rates of soil amendments on crop yield during organic transition. Compost, biochar, or a “50/50” mixture of the two on a C-equivalent basis were applied at a rate of 8 Mg C ha⁻¹ per varying application regimens, with and without cover crops, at two locations on the North Carolina Coastal Plain with sandy, low-C soils. It was hypothesized that the treatments would increase crop yield due to soil organic carbon–driven improvements in soil health, such as enhanced nutrient availability. Rather than increase yield, however, cover cropping and compost additions resulted in 15%–20% yield reductions for cash crops following a legume cover crop. The results suggest that the treatments, which provided N in excess of crop needs, drove late-season weed growth past the window for mechanical cultivation and led to subsequent yield reductions. Additionally, poor synchrony between cover crop N and cash crop demand was observed in a year where crimson clover was terminated late and its residue had a high C:N ratio (>30). These results were observed in a unique context, where organic management was implemented and N-related best practices concerning cover crop termination timing and fertilizer rate adjustment were intentionally deviated from in order to maximize the C input and to avoid yield differences resulting from varying N fertilizer rates, respectively. This study highlights the negative consequences of suboptimal N management and weed dynamics on crop productivity in Southeastern organic management systems with no rescue herbicides.