Winter cover crop root biomass yield in corn and soybean systems

Cover crop (CC) roots are critical for soil ecosystem service delivery including soil stabilization, C and nutrient cycling, soil health improvement, and others. However, most CC studies only evaluate CC aboveground biomass yield, neglecting the belowground portion of the plant. The objectives of this study were to quantify the impacts of (a) CC planting (pre- and post-harvest) dates and (b) early (2–4 wk before main crop planting) and late (at main crop planting) CC termination with and without corn (Zea mays L.) residue removal on root biomass yield. We assessed the effects of CC planting or termination dates on root biomass yield for surface 10 cm of soil at four sites through sampling at CC termination and separating roots from soil with a hydropneumatic elutriation system. Pre-harvest CC planting had limited and variable impacts on root biomass yield compared with post-harvest planting. Corn residue removal had no impact on root biomass yield. However, CC termination date had effects at the Irrigated but not at the Rainfed site. At the Irrigated site, late-terminated CCs doubled root biomass yield in both years compared to early terminated and no CC. At this site, under late-terminated CCs, root biomass yield was 2.8 Mg ha^–1 attributed to their higher aboveground biomass yield and later termination. At the Rainfed site, root biomass yield was 1.6 Mg ha^–1. Overall, late termination of CCs can increase root biomass yield; however, early planting into the cash crop did not consistently increase root biomass yield under the conditions of this study.