Performance of Site-Specific Nutrient Management for Mazandaran irrigated rice

Decision making on fertilizer application require knowledge of supply of nutrients from indigenous sources. Although, soil test is scientific and precision method to measure soil nutrient supplies but unfortunately most of farmers (99%) including rice farmers do not favor to use of the method. Also relationships between grain yield or nutrient accumulation and soil test were scattered. Presently, organic C are used to as a soil index in N fertilizer recommendation but it is no reliable indicator of soil N supply in irrigated rice. Research on P and K concluded that existing soil test methods had limited applicability to lowland rice. For the reasons, fertilizer recommendation for rice is generalized for different places. This is most inefficient method of fertilizer use. The recommendation does not consider spatial and climatic variability. Fertilizer recommendation through omission plot is a simple and holistic that it has not problems associated with soil test. Actually, Nutrient supplies from indigenous sources can be estimated by measuring plant nutrient uptake in nutrient omission plots. On-farm trials with 4 treatments (N0, P0, K0 and NPK + Zn) conducted in 5 farmer fields in Mazandaran during 2006-2007. Plot size varied 40-100m2 in different sites and seedlings were transplanted at 25 × 25cm spacing. Except desired nutrient, other nutrients applied in sufficient limit in the omission plot. Other cultural practices such as water management and crop protection were the same as those of local farmers. Fajr (high yielding variety) and Tarom (local variety) was transplanted in 4 sites and the other site was used Shojaee variety. The performance of treatments was measured in terms of grain yield at 14 % moisture content. 12 hill samples (2 series per plot) were taken at physiological maturity for measuring of dry matter and nutrient uptake. Dry matter, N, P and K uptake and rice grain yield has been evaluated. Results showed that there were significant difference among treatments in view of grain yield, dry matter and N, P and K uptake. Also, results showed that N is the most limiting nutrient so that it influenced P and K uptake. Yield gap between N0 and treatment with highest yield varied 14.3 to 38.4 percent and that of farmer fields and treatment with highest yield was about 4 to 20.7 percent among sites. Indigenous supplies of N, P and K varied with location and variety that indicating blanket recommendation should be revised. Experiment data demonstrate organic carbon is not reliable soil index to N fertilizer recommendation.