Fracionamento do fósforo e da matéria orgânica do solo em função de diferentes sistemas de cultivo e adubação

Abstract

The aim of the present research was to verify changes in organic matter fractions and soil phosphorus fractions (inorganic and organic) under different winter crops and fertilizer sources in grain production systems. The soil samples were collected at 0.00-0.05; 0.05-0.10; 0.10-0.20 and 0.20-0.40 m depths, in 2015 and 2016. A randomized complete block design was used in a split-plot scheme with four replications. In the summer crop all plots were cultivated with soybean. In the winter period, the plots received different crops (5): black oats, Crotalaria spectabilis, corn, corn + Brachiaria ruziziensis and wheat. In the subplots the three fertilizer sources were applied: organic, organomineral and mineral. The organic fertilizer used was the poultry litter, organomineral fertilizer was produced from the pelletizing of poultry litter and granular mineral fertilizer. The fulvic acid and humic acid fractions of the organic matter and the inorganic and organic phosphorus (P) levels were sensitive to the different winter crops. The humin fraction was little influenced by winter management. The organic fertilizer increases the carbon (C) level of the humic fractions of the organic matter and the inorganic and organic phosphorus level in the soil surface layer and does not alter the total organic carbon and oxidizable fractions of the soil. Mineral fertilizer increases the carbon level in the humic fractions of organic matter and the level of labile and moderately resistant organic phosphorus in the layer of 0.20-0.40 m. Cultures of wheat, corn and corn + Brachiaria in succession with soybean increase the levels of labile inorganic P in the layer 0.00-0.10 m, under organomineral and mineral fertilizer. The suppression of organomineral and mineral fertilization of sowing in the cover crops reduces the soil Pi levels.