Adjusting Ley Grassland Duration in Crop Rotations to Reconcile Food Production and Soil Carbon Stocks

Introduction of grasslands into cropping systems represents a strategy to ensure food production while reducing soil carbon losses. Yet, mixed crop and grassland management systems need to be evaluated in terms of achieving balanced food production and soil carbon (C) sustainability. The objectives of the study are: 1) to explore the impact of grassland duration on C input and soil C changes in agricultural systems; and 2) to test the variation in C input and soil C changes between rotations using grassland fertilized at high or low Nitrogen (N) application rates and their impacts on productivity. Field data regarding C input, soil C and crop production were collected during 2005–2016 from a longterm experimental site in Lusignan, France. Root biomass C was sampled annually, and the stable C isotope signature (δ13C) was determined to quantify the amount of C input from the root biomass. The results showed that integrating ley grassland in crop rotations increased the C input in the 0–30 and 0–60 cm soil layers (P \u3c 0.05) but showed limited improvements in shoot biomass C and grain yield of these crops. In addition, C stocks also increased in the 0-30 cm but not always in the 0-60 cm layer. Compared with cropland, permanent grassland did not show a greater C input, whereas the latter showed a C stock increase of 0.6–1.4 Mg C ha−1 yr−1. In addition, in crop rotations integrated with ley grassland together with high-N or low-N fertilization did not impact C input, changes in soil C at either 0-30 cm or 0-60 cm soil layers, or even the crop production, while the grass production decreased by 22.2%-66.6% for low-N fertilization. In conclusion, integrating ley grassland in crop rotations increases the C input and soil C stocks in top soil, while reducing the time and production of crops