Tailoring fertilizers for wetland rice to soil characteristics and yield target
1985
Reyes, R.Y. | Chavez, C.M. | Orticio, M.R. (International Rice Research Inst., Los Banos, Laguna (Philippines). Soil Chemistry Dept.)
Analyses revealed that over 65% of the soils were N deficient and over 57% were Zn deficient. Less than 25% were deficient in P or K. Most pH values were in the optimum range. In the dry season, 32 of the 52 sites produced significant responses to 80-0-0 of 0.4 to 2.0 t/ha with a mean of 1.3 t/ha. In the wet season, 43 of the 73 sites showed significant responses. Nearly 90% of the soils that responded to N in the two seasons contained less than 0.2% N or 2.0% C. Only 6 of the 125 sites showed a positive response to P in the presence of N. The varieties at these sites were early maturing ones. Responses to K in the presence of N and P were obtained only at 2 sites. For a yield of 5 t/ha, sandy soils containing less than 1% C need more than 80-30-30; clayey soils having more than 2% C need no N, P, K fertilizers. If the yield target was 5 t/ha, fertilizers could be saved and their efficiency maximized by: diverting N fertilizers from areas where the organic C content exceeds 2% to N deficient areas; omitting P fertilizers on soils containing more than 5 mg/kg Olsen P; omitting K fertilizers; growing P and Zn efficient varieties; and planting early
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