Effects of Long-term Application of Controlled-Release Urea on the Acid-Base Buffering System and Soil Fertility in Fluvo-aquic Soils

[Objective] To investigate the effects of long-term application of controlled-release urea on soil acidity, acid-base buffering capacity and fertility of northern calcareous tidal soils. [Methods] Based on a long-term field trial of positioning fertilization since 2008, two types of nitrogen fertilizers, blended controlled-release urea(CRF) and ordinary urea(BBF), and three levels of nitrogen application, namely, no nitrogen application (N 0 kg/hm2), constant nitrogen application (N 540 kg/hm2) and incremental nitrogen application (N 810 kg/hm2), were designed, and soil samples were collected from 0-80 cm during the ripening of the maize season of 2022 to determine the acid-base buffering capacity, soil calcium carbonate content and soil fertility of soil. Samples were collected from 0-80 cm soil at the maturity of the corn season in 2022 to determine the soil acid-base buffer capacity, soil calcium carbonate content and soil nutrients. [Results] (1) CRF slowed down the decline of soil buffer capacity and pH value caused by N application and alleviated the process of soil acidification. The buffer capacity of constant CRF and incremental CRF treatments increased by 5.22% and 11.17%, respectively, and the pH of constant CRF and incremental CRF treatments increased by 0.17 and 0.08 units, respectively, compared with that of constant BBF and incremental BBF. (2) CRF increased the soil cation exchange and exchangeable calcium and magnesium content and increased the active calcium carbonate content of the tillage soil, and the active calcium carbonate content of the constant CRF and incremental CRF treatments increased by 52.08% and 45.31% compared with that of the constant BBF and incremental BBF treatments. Meanwhile, CRF slowed down the loss of soil calcium carbonate content in deep soil layers. (3) CRF increased soil total nitrogen, organic matter, nitrate nitrogen and ammonium nitrogen content. [Conclusion] Long-term application of CRF alleviated soil acidification caused by nitrogen fertilizer application, increased soil active calcium carbonate content, and improved soil fertility.