Rice soil constraints and fertility management in the highlands of Madagascar
1995
Balasubramanian, V. | Rabeson, R. | Razafinjara, L. | Ratsimandresy, J.
Two of the most important factors that limit rice yield and response to fertilizers are soil OM content and water regime. Fertilizer response of, and use on rice will be limited in the absence of adequate water control. Phosphorus deficiency is common in all the soils, and must be corrected to obtain responses to other nutrients and to sustain rice soil productivity. Corrective P fertilization using heavy doses of P (100-200 kg/ha) is not possible for individual farmers, unless externally financed. Root dipping and nursery P fertilization appear to be efficient for small amounts of P. Nitrogen deficiency is common in mineral and slightly organic hydromorphic soils. Iron toxicity in poorly drained sites, and high OM content in peat soils, and low temperatures, reduce N use efficiency. Highly organic or peat soils respond mainly to P, while mineral soils require N and P application for high rice yields. Potassium becomes deficient only when crop residues or FYM are not regularly added to soils. Sulfur, Zn, and Si deficiencies occur in only isolated pockets. Assuming that a part of the crop residue is returned to the soil and some amount of FYM is added in each season, a dose of 45-60 kg N, 13-20 kg P, and 24-32 kg K/ha may be optimum for rough rice yields of 4-5 t/ha. Yield increases beyond this level with higher levels of fertilizer use are possible only with improvements in water control
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