Research on optimum fertilizer application
for lowland rice in karst area

【Objectives】Fertilization Indexes System was set up in Karst areas, the recommended rice fertilization system was then put forward and the reliability was verified, for the aim of high efficiency resources use and yield.【Method】 Forty four sets of the “3414” field experiment results were counted in the karst area of Guangxi province in China. The relative yields of 65%, 71%, 77%, 83% and 90% were used to divide the soil mineral N and readily available K into 6 grades, available P into 5 grades. The optimum N, P and K fertilizer rates were separately calculated using mathematics models of QEV3, QEV1 and LPP. Logarithmic models were used to simulate the correlation between the soil mineral nutrient contents and the optimum fertilizer rates. Ten fields were chosen for verification tests and laboratory analysis. The chlorophyll a, chlorophyll b, carotenoid contents, the activity of CAT, POD and SOD were tested at seedling stage. The yield components of rice and yield were investigated finally.【Result】 The 6 grades of soil mineral N availability are 1.21-1.28, 1.28-1.75, 1.75-2.21, 2.21-2.67, 2.67-3.22 and 3.22 g/kg, the corresponding N fertilizer rates are set as: 234-241, 202-234, 178-202, 158-178, 139-158 and 0-139 kg/hm2 respectively. The 5 grades of soil mineral P availability are 3.5-5.50, 5.50-11.70, 11.70-17.85, 17.85-25.00 and 25.00 mg/kg, the corresponding P2O5 fertilizer rates are 95-110, 70-95, 55-70, 44-55 and 0-44 kg/hm2 respectively. The 6 grades of soil mineral K availability are 6.99-19.50, 19.50-37.10, 37.10-54.60, 54.60-72.10, 72.10-92.50, 92.50 mg/kg, and thecorresponding K2O fertilizer rates are 146-191, 117-146, 101-117, 89-101, 78-89 and 0-78 kg/hm2 respectively. The plant height, grain number per panicle, filled grain number per panicle, POD and SOD activities showed significant differences among the differentrates of N, P and K fertilizer input rates in the 10 field experiments, indicating the Fertilization Indexes System is applicable tofertilization recommendation.【Conclusions】The Fertilization Indexes System could be helpful in the practical fertilization in farmland according to its soil mineral N, P and K levels. The method could be used for reference to build the similar fertilization system and the results also could be used in similar karst area to guide fertilization practice.