Phosphorus-lime interaction in a strongly acid upland soil grown to rice in Cavinti, Philippines
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Phosphorus deficiency and soil acidity are major constraints in strongly acid upland soils in the humid tropics (von Uexkull, 1986). This adverse ecosystem is gaining importance for food production due to population pressure. Therefore the need for proper soil fertility management of these soils is already strongly felt in some countries (Kamprath, 1980).
The trial was conducted in an Orthoxic Palehumult in Cavinti, Laguna beginning 1984 wet season. Different P sources and rates were applied with or without lime. Grain yields and soil properties were monitored to evaluate long-term effects of fertilizers and cropping on the soil. Soil P fractionation was also done after 6 cropping seasons.
Grain yields were highest when both P and lime were applied. Upland rice responded more to P during the initial years; but with time, the benefit of lime increased. Soil pH and Bray II P showed slight improvements with time. Yields in unfertilized plots gradually declined.
About 50% of total phosphorus was organic P. Iron phosphates were much greater than aluminum and calcium phosphates
Key wordsmanagement of P fertilizers and lime for dryland rice P deficiency and soil acidity in strongly acid soils
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