Antecipação da adubação fosfatada no inverno: produtividade das culturas e formas de P dosolo

Abstract

The phosphate fertilization anticipation is still a very complex issue, requiring further investigation on its effects on crop development, soil fertility and soil phosphorus (P) lability. Therefore, the aim of this work was to evaluate the effects of the phosphate fertilization anticipation, in the medium term, on the nutrition, yield and P use efficiency (PUE) of the spring-summer crops (maize and soybean), soil fertility attributes and soil P forms, under no-till (NT). The experiment was installed in September 2012, in Tibagi, Paraná, in a Oxisol with sandy-clay loam texture, in a randomized block design, with six replications and five treatments, namely: anticipation of 100, 75, 50, 25 and 0% of phosphate fertilization. The total dose of P2O5 during the year, for all treatments, corresponded to 90 kg ha-1, in the form of single superphosphate. The phosphate fertilization anticipation promoted changes in crop nutrition and in the soil chemical attributes, but with no impact on the crops dry matter and grain yields. There was no increase in the maize and soybean grain yields with the phosphate fertilization anticipation. For maize, when there was low water availability during the crop cycle, the anticipation of 50% of phosphate fertilization caused greater PUE compared to the anticipation of 75% of phosphate fertilization. For soybean, the phosphate fertilization anticipation tended to decrease grain yield and PUE. The lowest P anticipated doses and the P total application in the spring-summer sowing increased the levels of available P in the 5-10 cm soil layer during the course of the experiment. The management of phosphate fertilizer did not alter the levels of total organic carbon (TOC) in the 0-5 cm soil layer, keeping the levels high, benefiting the other soil chemical attributes, being fundamental for the success of the phosphate fertilization anticipation as a strategy of fertilization of systems. Regardless of the phosphate fertilization anticipation, organic P (oP) and residual P were the main components of soil total P, in greater quantity in the moderately labile and non-labile P fraction. The phosphate fertilization anticipation increased labile oP, total labile P and non-labile inorganic P bound to calcium, in the 0-5 cm soil layer, while phosphate fertilization in the spring-summer crop or the anticipation of only 25% of phosphate fertilization in winter it increased the levels of labile P, mainly oP, in addition to non-labile oP in the 5-10 cm layer. The TOC:oP ratio varied along the soil profile, with higher values obtained in the 0-5 cm soil layer (due to the higher TOC content in that layer) and below the 20 cm depth of the soil (due to the low mobility of P on the ground). However, all TOC:oP values were below 100, and a soil with a high content of available P could be considered. Under conditions of adequate soil fertility, stabilized NT and medium to high concentration of organic matter, the phosphate fertilization anticipation for maize and soybean is feasible, but without increases in crop yields.