Quantifying soil N pools and N2O emissions after application of chemical fertilizer and straw to a typical chernozem soil

An incubation experiment with equivalent N rates was conducted for 56 days using a typical black soil amended with chemical fertilizer with or without straw amendment using a N-15 cross-labeling technique. Compared with the chemical fertilizer treatment ((NCF)-N-15), chemical fertilizer combined with straw treatment (CF + S) showed a significantly higher (P < 0.05) contribution from applied N to microbial biomass N (BN) in the first 14 days and to particulate organic N (PON) and mineral-associated total N (MON) throughout the incubation. Straw application in the CF + S treatment significantly (P < 0.05) decreased the recovery of chemical fertilizer N as soil inorganic N except at day 3 but increased the recovery of chemical fertilizer N as BN before day 14 and as PON and MON from day 14 to the end of the incubation period. At the end of the incubation period, the total N2O-N emissions in the CF + S treatment increased significantly (P < 0.05) compared with the CF treatment, and the increase in N2O-N emissions was 73% from chemical fertilizer and 27% from straw N individually. Our results suggest that the combined application of chemical fertilizer and straw increased soil fertility together with an increase in N2O emissions in the typical black soil and the N2O emissions from straw cannot be ignored.