Discrepant long-term nitrogen mineralization in soil at early and later period after fertilization

Abstract. Soil mineralization, the process of organic to inorganic N which balances the N uptake by crop and N loss to environment, was always quantified by short-term (one day to thirty weeks) incubation experiment. However, the residuary effect of fertilization for N mineralization, especially manure application, is long-term existed, which is important and thought to be shaped by fertilization, soil properties, and climate. Here, we defined and examined dynamic shifts in long-term N mineralization (LT-N_min) between the first decade and later period after treated with no-fertilizer, conventional fertilizer with/without manure, fertilizer with stover return, in six typical agricultural zones over multiple decades. Soil total N (TN) and available N (AN) increased at rates of 10.1–58.2 mg· kg^-1·yr^-1 and 1.41–4.13 mg· kg^-1·yr^-1, respectively, by manure application at five sites, suggesting that manure enhanced both soil N storage and availability. The LT-N_min rate, defined as slope of the correlation between soil AN and TN indicated that AN increased by 70–81 mg per gram of TN increase, regardless of fertilization. Considering the fertilization period, the LT-N_min rate with manure application were higher in the first decade (42–181 mg·g^-1) than those in later period (33–92 mg·g^-1) at all sites. Variance partitioning analysis showed that soil properties contributed 35 % to LT-N_min in the first decade and increased to 45 % in the later period, while climatic conditions contributed 19 % first, but 8 % in the later period. Structural equation modeling suggested that LT-N_min was directly affected by annual temperature, with a standardized path coefficient of 0.86 in the first decade and 0.45 in the later period. These results showed that the residual N in soil was mineralized with a high rate in the first decade after fertilization and then slowed down, and the interactions between climate and soil had an enhanced impact on LT- N_min in later years of fertilization. This context-dependent understanding of interactions between soil properties, N cycling, and climate can thus inform soil management strategies to improve N availability and reduce the N loss to environment.