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ThesisItem Open Access Yield maximisation in rice (Oryza sativa L) in the acid sulphate soils of Kuttanad through systematic approach in fertilizer use(Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani, 2007) Annie, Koruth; KAU; Venugopal, V KCereals are the world’s major source of food for human nutrition. Among these, rice is very important and represents the staple diet for more than two-fifths (2.4 billion) of the world’s population, making it the most important food crop of the developing world. Rice is the staple food of Kerala and is the only cereal crop of significance to the food basket of the State. Kuttanad is the rice bowl of Kerala producing nearly 30% of the State’s rice output. The entire area is now planted with high yielding rice varieties adopting all improved agricultural practices including higher doses of fertilizers and pesticides. The problems associated with the application of heavy doses of fertilizers, leading to nutrient imbalance and economic loss to the farmer is a major constraint. Therefore improvement in soil health through balanced fertilization, leading to productivity increase and economic benefit to the farmer, will have a measurable impact on rice production in the state. With a view to realize the maximum economic yield in rice by optimizing the nutritional status of the soil, a series of experiments were undertaken under the present study entitled “Yield maximisation in rice (Oryza sativa L.) in the acid sulphate soils of Kuttanad through ‘systematic approach’ in fertilizer use”. This involved preliminary soil analysis, nutrient fixation study and green house nutrient survey to demarcate the nutrient constraints and also to optimize the soil nutrient status. The critical level of P & K for the soils of Kuttanad were also done since the basic concept of systematic approach is based on the critical level of nutrients in soil. Pot culture studies were undertaken to find out the critical level of P & K using maize as indicator crop. The soil test values of P & K were correlated with the per cent yield and a significant correlation was obtained only for P with yield. A quadratic relationship was observed with per cent yield and soil test P values. This relationship gave a critical level value of 11.17 mg I' 1 for P. But in the case of K, no such relationship was obtained. Fixation study conducted for P, K, Cu, Zn, Mn, S & B to find out if any of the applied plant nutrients, fixed or complexed abnormally with the soil indicated P, K, Zn, S & B as the limiting nutrients, and the optimum quantities of these limiting nutrients were determined as 224 mg f 1 P, 122 mg l"1 K, 5.8 mg f 1 Zn, 2 mg I' 1 S & 1.52 mg I' 1 B. The green house nutrient survey conducted to arrive at the optimum treatment revealed that, for formulating the optimum treatment, lime @ 0.07 g CaCC>3 100 ml' 1 soil, Ca @ 822.4 mg I'1, Mg @ 349 mg f 1, P, K, Zn, S & B at the above concentrations, Mo @ 2 mg I' 1 & N @ 100 mg I' 1 has to be added. There were 16 treatments. This experiment was conducted with Sorghum as indicator crop and the relative yield calculated from the biomass yield, recorded on the 45th day of planting revealed P only as the limiting nutrient for this particular soil. The quantity of P to be added to the optimum treatment was 224 mg I'1, which is 602 kg P ha'1. Since this is a very high and uneconomic dose for farmers to adopt, the Package of Practices Recommendations: Crops (POP) for medium duration rice variety, 45 kg P2O5 ha’1 was opted as the base and since P is the limiting nutrient, two higher doses, 60 & 75 kg P2O5 ha' 1 were tested as the three levels of P application. As balanced fertilization is a must for the rice crop, three levels of K were also included. Since K was not limiting, the POP recommended dose and two lower levels were tested, i.e., 15, 30 & 45 kg K2O ha'1. Thus the design for the field experiment was 3x3 Factorial RBD with an absolute control. Total 9+1 treatments. N @ 90 kg ha' 1 was applied to all treatment plots. The main effect of P & K and their interactions were studied. The field experiment was laid out for two consecutive seasons, Puncha (Rabi) 2004-05 (Nov. ’04 - March ’05) and Additional Crop (,Khan/) 2005 (May ’05 to Oct. ’05) in the experimental field of Rice Research Station (RRS), Moncompu, Kuttanad, Kerala. The medium duration rice variety, Uma (MO. 16) released from RRS, Moncompu with an average grain yield of 4.5 - 5.0 t ha' 1 was used for the experiment. The effect of these treatments on dry matter yield of shoot & root, soil & plant nutrient content and nutrient uptake of N, P & K at the critical stages of rice growth were studied. Biometric observations, yield and yield components were also recorded. For P, the limiting nutrient, significant differences in the phosphorus content of plant were observed when different doses of P were applied. The P content and uptake of grain and straw were not influenced during the Puncha season, while during the Additional Crop season it was significantly influenced by the varying doses of P. All the control plots recorded a significantly lower P content and uptake & low P soil status compared to treated plots on an average during both seasons. An increase in the application of K doses, resulted in a significant increase in the K status of soil during Puncha season, while during the Additional Crop season, this was not noticed and the treated plots were on par with control. With an increase in applied K, there was a significantly corresponding increase in K content in plant during the Puncha season, while during the Additional Crop season this was not so. The K content and uptake of grain and straw was not influenced during both seasons by the different doses of K but the treated plots recorded a significantly higher uptake