Relations between resin extractable soil phosphorus and response of vernalized garlic to phosphate fertilization of five soils, with and without organic fertilizer

摘要

Responses to phosphate fertilizing by vernalized garlic (Allium sativum, variety Roxo Perola de Caçador) were studied. To determine the calibration curve for phosphorus extracted with ion exchange resin, five soils of different textural groups, with and without organic fertilizer, were utilized. Two experiments, placed in 16 L pots, were carried out under greenhouse conditions, in the county of Botucatu, State of São Paulo, Brazil, from May to October, 1995 and 1996. Each of these experiments consisted of five soils at six levels of phosphorus (0, 50, 100, 200, 400, and 800 mg dm-3 of P). Organic fertilizer was applied only in the first year, at a rate of 40 t ha-1 of bovine decomposed manure. The application of organic matter made it difficult to discriminate the lower levels of applied P. High levels of phosphorus increased the chlorophyll, N, P, K, and Mn concentrations and reduced the Mg concentration in the leaves; P showed no antagonistic effects on the Zn absorption. The critical level of phosphorus, extracted with ion exchange resin, for the five soils was approximately 50 mg dm-3 of P, while the critical foliar concentration of phosphorus was 2.5 g kg-1 of P. Organic fertilizer may substitute phosphate fertilization, in the dosage recommended by the State of São Paulo, for vernalized garlic crop.