Mineralization characteristics of soil organic carbon under long-term fertilization management

Mineralization of soil organic carbon (SOC) is a vital link in carbon cycle in terrestrial ecosystems and has a significant effect on soil productivity and CO₂ exchange in the soil-atmosphere system. Studies on the response of SOC mineralization and its temperature sensitivity to long-term fertilization could provide essential information for the understanding of SOC dynamics in semiarid agro-ecosystems. In this paper, we analyzed the characteristics of SOC mineralization for soils collected from legume-grain rotation systems with 27 years of application history of different fertilizers in the semiarid Loess Plateau of China. We also analyzed SOC mineralization sensitivity to temperature and its response to different fertilizations. The objective of the study was to build a deeper insight into how SOC mineralization responds to long-term fertilization in semiarid agro-ecosystems. The results showed that SOC mineralization rates were high at the initial stage and then slowly decreased at different temperature (15 ℃ and 25 ℃) and fertilization treatments. Fertilization and cultivation temperature significantly influenced SOC mineralization. Compared with the no fertilization treatment (control), long-term application of phosphorus (P), combined nitrogen and phosphorus (NP), and combined nitrogen, phosphorus manure (NPM) increased cumulative mineralized SOC (C_min) by 41%, 85% and 89%, respectively, at 15 ℃, and by 7%, 46% and 77%, respectively, and 25 ℃. Also compared with control, P, NP and NPM application conditions decreased SOC mineralization sensitivity to temperature by 25%, 21% and 6%, respectively. Long-term fertilization changed the parameters of SOC mineralization, which varied with fertilizer type and cultivation temperature. SOC mineralization potential (C_p) of P, NP and NPM treatments increased by 29%, 65% and 48%, respectively, compared with that of control at 15 ℃. However, at 25 ℃, C_p increased by 2% under NP condition, increased by 21% under NPM condition, and decreased by 36% under P treatment compared with that under control. SOC mineralization constant (k) varied slightly at 15 ℃, but greatly increased due to fertilization at 25 ℃. Additionally at 25 ℃, cumulative Cmin and C_p were enhanced positively with increasing of both SOC and soil total nitrogen content. But at 15 ℃, Cmin and C_p were barely positively correlated with SOC and soil nitrogen. In conclusion, long-term fertilization increased SOC mineralization in legume-grain rotation systems in semiarid Loess Plateau, and decreased SOC mineralization sensitivity to temperature.