The effects of long-term application of nitrogen + phosphate + potassium (NPK), NPK + compost, NPK + silicate, and compost on nitrogen mineralization and soil chemical properties were studied in paddy soils with a fine, silty loamy-textured alluvial deposit. Fertilizers were continuously applied with NPK, NPK + compost, and compost from 1967 to 2004 and NPK + silicate had been added since 1981. The breakdown of NH₄-N mineralized from wet and dry soil by flooding culture for four weeks in 30^oC was observed in the following order: NPK + compost > NPK > compost > NPK + silicate from wet soil and NPK+compost > compost > NPK + silicate > NPK from dry soil. The air-drying effect from soil treated under long term with the same application was seen in the following order: NPK + compost (42) > Compost (35) > NPK + silicate (25.3) > NPK (19.9 mg dry soil 100g^-1). According to treatments, soil pH was around 5.3-5.7 except for plots applied with NPK + silicate. With regard to the plots of NPK, NPK + silicate and NPK + compost showed high values of soil pH but were low in compost. Soil Organic Matter (SOM) content was high in the plots of NPK + compost and compost only showing 32g kg^-1 to 37g kg^-1 and 30g kg^-1 to 34g kg^-1, respectively. In plots with compost, SOM was 27g kg-1 to 31g kg^-1. NPK + compost and NPK increased soil phosphate to 3.5mg kg^-1 and 2.4mg kg^-1 in average, respectively. In the case of soil silicate, the content annually decreased to 14mg kg^-1 for 10 years from 62mg kg^-1 in 1981, when NPK+silicate were first applied. After 10 years of silicate application, the rate clearly increased to 37mg kg^-1 per year until 2001, the 20th year of experimenting with silicate. Keywords: rice, compost, silicate, long-term application, mineralization.