Optimized crop rotations increase biomass production without significantly changing soil carbon and nitrogen stock

Abstract

To meet the growing challenges for food security, renewable resource production and climate change adaptation, optimized crop rotations (OCRs) should aim to maximize biomass production and export from the field while minimizing carbon (C) and nitrogen (N) footprints. However, the effects of OCRs on aboveground biomass production and soil C and N stock as well as the potential links between them remain poorly understood. In this study in Denmark, we harvested all aboveground biomass and simultaneously investigated soil C and N content and stock in two continuous monocultures (CMs) as well as in four OCRs. Across five-year continuous observations, OCRs significantly increased cumulative aboveground biomass production by 23% compared to CMs. There was no significant difference between OCRs and CMs in soil C and N content in any of the soil layers (0–20, 20–50, and 50–100 cm) after the five years. Moreover, OCRs had no effect on top layer soil C and N stock compared to CMs, even when examined by equivalent soil mass. Slight reductions in soil C and N stock after five years in both OCRs and CMs did not relate to the changes in aboveground biomass production. Our results highlight that it is feasible to produce more biomass for biorefineries in OCRs than in CMs and the reductions in soil C and N stock over time seem similar for the two systems. Longer-term continuous observations are called for to underpin these results.