Abstract

                                An incubation experiment was carried out to know if any of the applied plant nutrients, viz., P, K, S, Zn, Cu, Mn and B react (fix or complex) abnormally with the experimental soil. On the basis of critical level of nutrient in the soil and nutrient sorption curves, an Optimum Nutrient Treatment (ONT) consisting of P, K and Zn besides N, which are deficient in the soil, was formulated for the experimental soil. The evolved ONT was tested by means of a green house nutrient survey experiment with sorghum (Co 27) as the test crop. These results confirmed that the exclusion of N, P, K and Zn significantly reduced the dry matter yield. But the addition of other nutrients like Ca, Mg, S, Cu, Fe, Mn, Mo and B did not significantly influence the dry matter yield. A field experiment was conducted to evolve the fertilizer optima for rice with a treatment structure developed based on the ONT. Short duration rice (ADT 36) was grown during Kuruvai season (June-September, 1999) and medium duration rice (Co 43) during thaladi season (October, 1999- January, 2000). From a fit of the grain yield data on a quadratic polynomial surface, the optimum amounts of nutrients which ensures balanced fertilization were evolved. The results revealed that 175, 54, 50 and 30 kg ha for ADT 36 rice and 165, 63, 65 and 30 kg ha" for Co 43 rice, respectively of N, P,O,,K,O and ZnSO, 7H,O ha¹ were the optimum doses of nutrients in this soil. Economics of balanced fertilization through this systematic approach was compared with the blanket fertilizer recommendation by test verification in the field. The results revealed that the rice yield as well as profit were higher with balanced fertilization by systematic approach as compared to the blanket fertilizer recommendation

Key words : Rice, Yield limiting nutrients, Fertilizer optima