Frações de fósforo no solo em função da calagem, adubação fosfatada e plantio de leguminosas em área de expansão de canavial

Abstract

Phosphorus is one of the nutrients that most limits plant growth, so the adoption of innovative techniques for the cultivation system is essential to ensure the efficiency of use of this nutrient. Thus, the objective was to evaluate the changes in P forms in the soil caused by liming, corrective phosphate fertilization and leguminous cultivation prior to the planting of sugarcane, in an expansion area, in a restrictive environment. The experiment was carried out in Caarapó-MS, in a psamitic Dystrophic Red Latosol, in a randomized block design in sub-divided plots, with three replications. In the plots, two doses of limestone (6 and 12 Mg ha-1) were evaluated; in the subplots, the effect of three predecessor cultures to the planting of sugarcane was evaluated (soybean residue, Crotalaria spectabilis and C. juncea); And in the sub-subplots three doses of calcined thermophosphate (0, 380 and 760 kg ha-1). Soil samples were collected at 18 months after application of liming and soil phosphate treatments. Phosphorus content of different fractions (labile, moderately labile and non-labile) in three soil layers 0 to 0.1; 0.1 to 0.2 and 0.2 to 0.4 m, as well as sugarcane leaf content, production of stalks and sugar. The results were submitted to the Tukey test at 5% probability. In the layer from 0 to 0.1 m, the labile fraction (P resin) for all P doses was higher when 12 Mg ha-1 of limestone was applied. Regarding the predecessor cultures, at doses of 380 and 760 kg ha-1, C. juncea promoted a greater amount of available P. In the layer from 0.1 to 0.2 m, for the dose of 380 kg ha-1 of thermophosphate, the P resin content was higher when the highest dose of limestone was applied; at the dose of 760 kg ha-1 of thermophosphate, the P resin content in C. juncea residue was higher in relation to soybean. In the layer of 0.2 to 0.4 m, P resin at rates of 0 and 380 kg ha-1 was higher in liming with 12 Mg ha-1. It was concluded that the forms of phosphorus in the soil were altered as a function of liming, corrective phosphate fertilization and the cultivation of leguminous plants as predecessor plants to sugarcane. Sunn crotalaria promoted higher phosphorus content in the more labile fractions, especially with the use of 12 Mg ha-1 up to 40 cm of depth. C. juncea associated with liming with 12 Mg ha-1 and soybean residue with liming with 6 Mg ha-1, were the best combinations for the effect of phosphorus availability for sugarcane. Since, the dose of 6 Mg ha-1 of limestone associated with soybean residue, provided greater accumulated production.