Effect of long-term fertilization on distribution of aggregates and organic carbon and total nitrogen contents in a brown soil

Objectives The purpose of this study was to investigate effects of different fertilization treatments on soil aggregate distribution, organic carbon and total nitrogen in maize-maize-soybean rotation system, and to gain insight into the mechanism of soil fertility improvement and soil structure. Methods The treatments were as follows:the control (CK), chemical fertilizer (NPK), low-level organic manure (M1), low-level organic fertilizer and chemical fertilizer (M1NPK), high-level organic manure (M2), and high-level organic fertilizer and chemical fertilizer (M2NPK). The soil samples at 0-20 cm and 20-40 cm soil layers were analyzed to understand the characteristics for their water-stable aggregates ( 1 mm, 1-0.5 mm, 0.5-0.25 mm, 0.25-0.053 mm and 0.053 mm), the contents of SOC and TN and partitioning proportions of SOC and TN. Results The effects of the long-term fertilization on aggregates distribution, carbon and nitrogen in brown soil at the 0-20 cm layer were greater than those at the 20-40 cm layer, and the contents of soil organic carbon (SOC) and total nitrogen (TN) decreased with soil depth increasing. The distribution of aggregates, and carbon and nitrogen in agglomerates were mainly in the clay particles (above 40%). Compared with CK, NPK significantly increased the content of clay particles, decreased the contents of macro-aggregates and micro-aggregates significantly. M1 and M2 significantly increased the contents of 1 mm aggregates and SOC, and carbon storage in 0.25 mm aggregates. Compared with NPK, the carbon storage ratios of M1NPK and M2NPK were increased in the order of 0.5-0.25 mm (M1NPK), 1-0.5 mm and 1 mm aggregates. The proportion of carbon storage of 0.25 mm aggregates in the M2NPK was the highest, and that of total nitrogen was similar to that of organic carbon. Conclusions Continuous organic and inorganic combinations of brown soil can significantly increase the amount of large aggregates, SOC, TN content and its carbon and nitrogen ratio, it is an effective fertilization measure to improve soil quality and soil structure.