Biomass yield, yield stability and soil carbon and nitrogen content under cropping systems destined for biorefineries

Abstract

Sustainable agriculture should aim to increase biomass yield and yield stability, while protecting soil carbon (C) and nitrogen (N) content. However, few studies have concurrently explored changes in biomass yield, yield stability and soil C and N content under different cropping systems targeting biorefinery. In this study, 10 different cropping systems were simultaneously investigated from 2012 to 2017 in central Denmark on a loamy sand soil, including (1) two continuous monocultures of annual crops, (2) one optimized crop rotation, (3) five intensively fertilized perennial grasses, and (4) two grass-legume mixtures without nitrogen (N) fertilization. Our results showed that biomass yield and yield stability differed highly across the cropping systems, highlighting crop-specific characteristics. Of the 10 cropping systems, tall fescue significantly increased soil C and N content at 0–20 cm depth, while sustaining high biomass yield and yield stability. There was no clear relationship between biomass yield, yield stability and changes in soil C and N content, challenging some recent findings on the conflicts between increasing biomass yield and protecting soil C and N content. Indeed, the lack of relationships suggest that there is considerable potential to increase biomass yield and yield stability without compromising soil C and N content through selecting proper cropping systems and managements. Altogether, our results underscore how crop-specific documentation of biomass yield, yield stability and changes in soil C and N content on the same experimental platform can advance the understanding of sustainable agriculture for biorefineries, although long-term continuous observations are still required to better clarify the relations between them.