Optimizing STCR-IPNS fertilizer prescription for targeted rice yield in North Eastern agro climatic zone of Tamil Nadu

Rice is the major crop in the North Eastern zone of Tamil Nadu. In Tiruvallur district, rice is the major crop cultivated in 96967 ha with a share of 6.7% of the state. At present, the productivity of rice in Tiruvallur district is 4200 kg ha-1 . Due to intensive cropping and application of chemical fertiliz- ers without organic manures, the organic matter content of the soils in Tiru- vallur district is very low in most of the areas with the occurrence of multi- nutrient deficiencies, especially zinc and iron deficiency in rice. In Soil Test Crop Response-Integrated Plant Nutrition System (STCR-IPNS) technology, the fertilizer doses are tailored to specific yield target levels, considering the nutrient requirement of the crop, and the contribution of nutrients from soil, fertilizers, and organic manures. The field experiments were conducted during samba season in irrigated rice to refine the existing Fertilizer Pre- scription Equations (FPEs) for specific yield target levels on the Kadambady soil series in the Tiruvallur district for sustainable rice production and soil quality. Observation on growth and yield attributes was recorded. Grain yield, straw yield, and dry matter production were recorded. Post-harvest soil and plant samples were collected from all the plots. Based on the initial soil analysis of available NPK (Kg ha-1 ) and NPK content in FYM, the STCR- based IPNS fertilizer recommendations were worked out with FPEs of Irugur soil series (Rabi) under yield target levels of 50, 60, and 70 q ha-1 . Using the data on the grain yield, total uptake of NPK, initial soil test values for availa- ble NPK, and doses of fertilizer N, P2O5, K2O, and FYM applied, the basic pa- rameters, viz., the nutrient requirement (NR), contribution of nutrients from soil (Cs), fertilizer (Cf), response ratio (RR), and farmyard manure (Cfym) were computed. Using the basic parameters, viz., NR, Cs, Cf, and Cfym, the FPEs were developed under NPK alone and IPNS. From the test verification trials, the STCR-based fertilizer prescriptions under IPNS for 7 t ha-1 , i.e., applica- tion of fertilizer N, P2O5 and K2O based on initial soil test values with FYM at 12.5 t ha-1 (with a manurial composition of N: 0.48 %, P: 0.23%, K: 0.42 %, and moisture: 24%) contributed fertilizer N, P2O5 and K2O at 40:20:32 kg ha-1 from the recommended dose of fertilizers based on soil test values. This can be recommended for achieving higher yield, RR and benefit-cost ratio (BCR) for rice. The increase in yield with STCR-IPNS-7 t ha-1 was 41.5% over blanket (100% RDF alone), 24.8% over blanket + FYM at 12.5 t ha-1 ,and 56.7% over farmer’s practice. The increase in RR was 4.54, 1.98 and 5.25 kg kg-1 due to STCR-IPNS-7 t ha-1over blanket (100% RDF alone), blanket + FYM at 12.5 t ha- 1 and farmer’s practice respectively, on Kadambady soil series and allied soil series, especially in Tiruvallur district of North Eastern agro climatic zone of Tamil Nadu.