Abstract
The objectives of this study were to monitor the changes in soil solution nutrients and to evaluate their effect on rice uptake and yield. The changes of chemical characteristics of paddy soil solution were examined from the 58th fertilization experiment in which the continuous rice cropping experiment started in 1954 at the National Academy of Agricultural Science. The treatments were no fertilization (No fert.), inorganic fertilization(NPK), inorganic fertilizer plus rice straw compost (NPKC) and inorganic fertilizer plus silicate and limefertilizer as a soil amendment (NPKCLS). The fertilizers were added at rates of standard fertilizer application rate in which nitrogen (N), phosphate (P₂O 5 ), potassium (K₂O), and sililcate (SiO₂) were applied at rates of 75~150 kg ha -1 , 70~86 kg ha -1 , 75~86 kg ha -1 , and 7.5 Mg ha -1 respectively and lime was applied to neutralize soil acidity until 6.5. Average Electrical Conductivity (EC) of soil solution in NPKCLS and NPKC ranged from 1.16 to 2.00 dS m -1 . The NH4+ and K+ levels in NPKCLS and NPKC were higher than that of the other treatments, due to high supply power of rice straw compost. The content of H₃SiO₄ - was higher in NPKCLS because of silicate application. The dominant ions in soil solution were Ca 2+ , Mg 2+ and Na + among cations and HCO₃ - , SO₄ 2- , and Cl - among anions in all treatments. The continuous application of inorganic fertilizers plus rice straw compost (NPKC) and silicate fertilizer (NPKCLS) led to the changes of various chemical composition in soil solutions. Also, they had a significant impact on the improvement of rice inorganic uptake and grain yield. Especially, inorganic uptake by rice in NPKC and NPKCLS significantly increased than those in NPK plot; 14~46% for T-N, 32~36% for P, 43~57% for K, and 45~77% for Si. Therefore, the combined application of inorganic fertilizers with organic compost as a soil amendment is considered as the best fertilization practice in the continuous rice cropping for the improvement of crop productivity and soil fertility.
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