AVAILABILITY OF PHOSPHORUS IN SOIL CULTIVATED WITH BRACHIARIA IN ROTATION WITH SOYBEAN

Abstract

In no tillage system it is possible to get benefits by the capacity of some plant species with greater ability to absorb phosphorus, changing the dynamics of the nutrient in the soil, and thus improve the availability of this nutrient for subsequent crops. The main objective of this study it is to assess the availability of phosphorus by brachiaria and its effect in soybeans crop. Three experiments will be conducted in Botucatu, SP. The first test begun to be conducted in no-tillage at 12 years ago. Treatments in the plots are areas that received two P sources (natural and soluble) spreaded over the soil in the begin of the offseason, totaling 400 kg P2O5 ha-1 since the implementation of the system, and more a control. In subplot treatments there are: the presence and absence of Brachiaria in offseason; and 3 doses of P in soybean planting, in subplots. It will be evaluated soil fertility before soybeans crop, the nutrient content and dry matter of Brachiaria and soybeans, and soybean yield. The second and third tests will be carried in a greenhouse, using soils from plots of the previous experiment, with contrasting species for the ability of P uptake, maize and lupine. The treatments are: soil that received or not soluble P spreaded over the soil; soil from plots that received 0 or 60 kg ha-1 de P2O5 in soybean sowings, all with and without Brachiaria in the offseason. It will be evaluated P fractions in rhizosphere and bulk soil, dry matter production and P uptake, shoot: root relation, length and root diameter. The results will be submitted to analysis of variance and means were compared by t test (LSD) at 5% probability.