Legacies of winter cover crops lead to opposing optimal N fertilisation rates and yields in first and second subsequent crops on contrasting soils

Abstract

Winter cover crops (CCs) provide substantial agronomic and environmental benefits, yet their influence on nitrogen (N) fertilization requirements and yield outcomes for subsequent crops remains underexplored. This study investigates the economic optimal nitrogen rates (EONRs) and corresponding yield effects for first (silage maize or sugar beet) and second (winter wheat) succeeding crops following CCs. Four CC species from different functional groups were compared to a bare fallow control on contrasting sandy and loamy soils across four German field sites over two consecutive cropping sequences. Results revealed opposing effects: reduced EONR and increased N use efficiency on sandy soils in silage maize sequences, particularly following oil radish and rye CCs, but increased EONR on loamy soils for sugar beet sequences, with vetch CC showing the most favourable outcomes. Yield impacts varied by CC type and soil, with oil radish consistently enhancing yields across sites. However, CC effects on EONR were not correlated with pre-winter N uptake in CC biomass, challenging simple N budgeting practices. Environmental analysis highlighted potential greenhouse gas savings via reduced fertilizer inputs on sandy soils but increased upstream emissions on loamy sites. These findings emphasize the need for site-specific CC selection to balance economic and environmental benefits, with oil radish and vetch emerging as optimal choices in our trials for sandy and loamy soils, respectively.

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