Carbon fractions and productivity under changed climate scenario in soybean–wheat system

Global climate change is anticipated to have a tremendous influence on crop productivity and nutrient cycling in legume-based cropping systems. The effect of long-term application of manure and fertilizers on the dynamics of soil organic carbon (SOC) pools and soil physical properties was studied in a soybean (Glycine max Merr. L)–wheat (Triticum aestivum L.) system. The temperature sensitivity of C pools and the alterations in microbial composition were determined at 25, 35, and 45 °C. Higher levels of microbial biomass C (MBC) and nitrogen (MBN), water soluble carbon (WSC), acid hydrolysable carbohydrates (AHC), particulate organic matter carbon (POMC) and nitrogen (POMN) were observed in the NPK + FYM at a depth of 0–15 cm. Irrespective of the treatment, micro aggregates (53–250 μm) were a major aggregate size class, comprising 45–57% of the total soil aggregates, followed by macro aggregates (250–2000 μm at 37.8–45%). Microbial respiration rate increased by 13.9% in most recalcitrant pools (<53 μm) at 45 °C than at 25 °C. Furthermore, data on labile C (A0) revealed a 4.9–55.4% increase in the substrate pools and a 10.5–32.5% increase in mineralization rate (k) with these treatments at 25–45 °C in 250–2000 μm aggregates. AHC and POMC content decreased by 23–37% and 12–23% of SOC, respectively, when the temperature was raised from 25 to 45 °C. It is concluded the gradual depletion of nutrients, structural degradation and changes in microbial composition might have collectively contributed to the decline in crop yields. It was suggested that temperature has a strong effect on C mineralization, depending on the types and extents of substrate utilization. Seasonal rainfall, maximum and minimum temperature and SOC had jointly explained 12–41% of variation in soybean production in NP, NPK and NPK + FYM treatments. However, balanced use of NPK plus FYM is an important management option to arrest the decline of crop yield.

► We examined long-term effect of manure and fertilizers application on soil organic carbon pools
► We studied temperature sensitivity of C pools and alterations in microbial composition
► Established the relationship between productivity and climatic parameters
► Physico-chemical degradation and changes in microbial composition may decline in crop yields.