Site-specific nutrient management in rice in Eastern India using a modeling approach

Rice is the staple food of about 50% of the world's population. Rice yields in many parts of south Asia, however, are declining due to conventional blanket and imbalanced use of fertilizers. Fertilizer application based on quantitative approaches such as simulation modeling can assist in improving yields and nutrient use efficiency in rice. Field experiments were conducted in 20 sites in Eastern India to assess the soil supply, requirement and internal efficiency of N, P, K and Zn in rice. The data were used to calibrate the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model for site-specific, balanced fertilizer recommendations. The parameters of maximum accumulation (a) and dilution (d) of N (31, 87), P (192, 678), K (33, 81) and Zn (32488, 153125) in plants were developed, which can be used as the standard parameters in the QUEFTS model for rice. The relationships between chemical properties and nutrient supplying capacity of soil were also established. Grain yield of rice showed good correlation with N (R(2) = 0.95**), P (R(2) = 0.71**), K (R(2) = 0.98**) and Zn uptake (R(2) = 0.57*). The NPK ratio to produce 1 Mg grain yield of rice was derived to be 6.5: 1.0: 6.8. Running the calibrated model with observed field data from different locations in India with different amounts of N, P, K and Zn produced a good fit between measured and calculated yields. The results suggested that the validated QUEFTS model could be used for calculating fertilizer requirements and improved site-specific and balanced fertilizer management in rice.