Carbon fluxes in spring wheat agroecosystem in India

Carbon fluxes from agroecosystems contribute to the variability of the carbon cycle and atmospheric [CO2]. This study used the Integrated Science Assessment Model (ISAM) to investigate carbon fluxes and their variability in Indian spring wheat agroecosystems. First, ISAM was run in site-scale mode to validate GPP, TER, and NEP over an experimental spring wheat site in north India. When compared to flux-tower observations, the spring wheat module in ISAM outperformed the generic crop model. Following that, regional-scale runs were performed to simulate carbon fluxes across the country from 1980 to 2016. The results revealed that fluxes vary significantly across regions, owing primarily to differences in planting dates. Fluxes peak earlier in the country's eastern and central regions, where crops are planted earlier. During the study period, all fluxes show statistically significant increasing trends (p.01). GPP, NPP, Autotrophic Respiration (Ra), and Heterotrophic Respiration (Rh) increased at 1.272, 0.945, 0.579, 0.328, and 0.366 TgC/yr(-2), respectively. Numerical experiments were conducted to investigate how natural forcings such as changing temperature and [CO2] levels and agricultural management practices such as nitrogen fertilization and water availability could contribute to the rising trends. The experiments revealed that increasing [CO2], nitrogen fertilization, and irrigation water contributed to increased carbon fluxes, with nitrogen fertilization having the most significant effect.