Responses of winter wheat yield and soil organic carbon to long-term (1990–2021) fertilization regimes under inter-annual weather variation in the Loess Plateau

Understanding the long-term responses of crop yield and soil organic carbon to fertilization is necessary to sustain food supply in a context of global change. The time-course of winter wheat yield and soil organic carbon were established in a 31-year long experiment with four fertilization regimes: unfertilized control; fertilized with mineral nitrogen and phosphorus, NP; fertilized with mineral N, P and K, NPK; and fertilized with manure and mineral NPK, MNPK. Over the time series, mean temperature increased at 0.054 ℃ year−1 (i.e. 1.67 degrees over the course of the experiment) and annual precipitation increased at 8.9 mm year−1. Yield did not show trends in unfertilized controls, increased at 210 kg ha−1 year−1 in the first 20 years and decreased slightly afterwards in the NP and NPK treatments, and increased at 310 kg ha−1 in the MNPK treatment until 2006, and leveled off afterwards. Soil organic carbon increased linearly with rates from 0.05 g kg−1 year−1 in unfertilized controls to 0.24 g kg−1 year−1 in MNPK. In fertilized crops, yield correlated nonlinearly with annual precipitation, and linearly with average temperature during the growing season. Across fertilizer treatments, yield correlated nonlinearly with soil organic carbon and the thresholds of soil organic carbon for peak yield increased with water supply. It is concluded that the combination of organic and inorganic fertilizers contributed to yield and soil organic carbon against the background of a warmer and wetter climate.