Abstract: Soil acidification of large areas of paddy fields in southern China has become an important problem in rice production. Therefore, how to ameliorate or remedy the acidifying paddy soil and to exposit its mechanism has important theoretical and practical significance for rebuilding healthy soils and guaranteeing national food security. Although lime has already been extensively used to remedy acidified soils, long-term application of a large amount of lime would not only cause the soil to harden, but also disturb the balance between calcium, potassium and magnesium in the soil. Given the advantages of lower solubility and comprehensive nutrient supply, fertilizer of calcium silicon magnesium potassium (CSMP) may be used as an alternative. The aim of this study was to clarify the functions of CSMP and its effects on soil acidification in paddy fields. A four-year field experiment was conducted to investigate the dynamics of soil pH, exchangeable acidi-ty, exchangeable base cation and available silicon, as well as 0~30 cm pH buffer capacity (pHBC), net base production under CSMP fertilization in the paddy soil. There were five treatments, i.e. CK (traditional fertilization practice of the local farmers), treatment I (CK plus 750 kg·hm^-2 CSMP); treatment II (CK plus 1125 kg·hm^-2 CSMP), treatment III (CK plus 1500 kg·hm^-2 CSMP), and treatment IV (CK plus 1875 kg·hm^-2 CSMP). The results showed that the traditional fertilization practice of the local farmers resulted in a decline of soil pH, soil exchangeable base cation and base saturation year by year, but soil exchangeable acid was increased with year. Conversely, CSPM fertlization significantly raised soil pH, with the magnitude of increases positively depending on the number of application times or application rate. Continuous and repeated application of CSMP effectively promoted the accumulation of exchangeable base cation and the consumption of soil exchangeable acid in paddy soil, especially for the accumulation of soil exchangeable Ca²⁺, Mg²⁺ and the consumption of soil exchangeable Al³⁺. Furthermore, the more amount of CSPM application resulted in the more accumulation or consumption, but with relatively slower rate. The exchangeable base cation and alkali released by CSMP contributed 108.8% to the total reduction of soil exchangeable acid, suggesting that it was the main path to reduce soil exchangeable acid. Meanwhile, CSMP application improved soil acidity in paddy field, with the content of available silicon increased year by year and the increase amplitude became larger with the more amount of CSMP application. The traditional fertilization of local farmers resulted in soil acidification, with a acidification rate was 2.86 kmol H⁺·hm^-2·a^-1. CSMP application could effectively control soil acidification, producing a lot of alkalinity with net alkalinity production of 9.93-13.82 kmol OH^-·hm^-2·a^-1. CSPM could release Ca²⁺, Mg²⁺ and alkali, which would mitigate soil acidification in paddy fields.

Key words: fertilizer of calcium silicon magnesium potassium (CSMP), soil improvement, exchangeable base cations, soil pH, soil available silicon