How does grain legume inclusion affect yield and N dynamics in a sugar beet crop rotation?

Abstract Grain legume cultivation may offer benefits for subsequent crops regarding N supply and fertilizer reductions. However, legume effects on subsequently grown sugar beet ( Beta vulgaris L.), before which cover crops may be cultivated, were hardly studied so far. In this study, pea ( Pisum sativum L.) was compared to wheat ( Triticum aestivum L.) as preceding crop before a succession of mustard ( Sinapis alba L.) cover crop, sugar beet and winter wheat over four sequences in a long-term crop rotation trial near Göttingen, Central Germany. For all crops, yield, biomass, N uptake and soil mineral nitrogen before winter and in spring were analyzed. Pea compared to wheat as pre-crop was found to largely increase subsequent mustard cover crop biomass (+ 81%) and N uptake (+ 116%) as well as soil mineral nitrogen after mustard termination (+ 97%). This pre-crop effect was passed on to the following sugar beet which had higher taproot (+ 6%) and leaf biomass (+ 15%) as well as sugar yield (+ 4%) after pea, despite a partially lower N fertilization than after wheat. After sugar beet, soil mineral nitrogen and subsequent wheat yields were similar independent of the preceding main crops, despite a higher N amount in the sugar beet residues after pea. This may hint at a loss of N, necessitating careful adjustments of sugar beet fertilization. Overall, we showed in our field trial that a preceding legume main crop offers benefits for subsequent sugar beet which could be used for a more sustainable sugar beet cultivation, using less fertilizer without losing yield.