Manipulating cover crop growth by adjusting sowing time and cereal inter-row spacing to enhance residual nitrogen effects

Abstract

Legume-based cover crop (CC) mixtures can increase nitrogen (N) availability in arable systems, reducing the need for external N inputs, as they retain soil N and fix atmospheric N2. However, they need sufficient biomass accumulation to influence soil N availability. Early establishment through undersowing can improve CC growth and plant N accumulation, but competition with the main crop should be minimized. This study aimed to investigate the effect of main crop inter-row spacing (12, 18, 24 cm), manure application (without, with) and CC undersowing (early, late, no cover crop) on N accumulation in a legume-based CC mixture and the residual N effect on the following crop. We conducted a field experiment in Denmark with spring wheat as main crop and spring oat as following crop during two pairs of consecutive seasons (2015–2016, 2016–2017). Spring wheat yield was unaffected by inter-row spacing, but it was increased by manure application. In manure treatments, larger inter-row spacing and early CC undersowing increased CC N accumulation by up to 260% (30 kg N ha−1), due to increased light availability. Treatments without manure and with early undersowing gave the highest CC N accumulation, resulting in N fertilizer replacement values of 13–50 kg N ha−1. Thus, increasing main crop inter-row spacing and early undersowing can improve CC growth and N accumulation, and well established legume-based CC could help to stabilize crop yield over time, as suggested by the similar cumulative grain yields (spring wheat + oat) without and with manure.