Disponibilização de nutrientes por plantas de cobertura do solo

Abstract

The nutrient cycling is closely related to the soil absorption capacity of the plants. The contribution of vegetal residues to the soil surface allows a greater cycling of the nutrients favoring the assimilation by the cultures in succession. In the rates of straw decomposition and nutrient release, the quality of the residue as the main regulatory parameter is marked, with the difference between poaceous, fabaceous and brassic. Thus, the objective of this work was to quantify the straw decomposition rate and the release of Nitrogen, Phosphorus, Potassium, Calcium and Magnesium from winter cover crops under no - tillage system. The evaluations took place in the 2015/2016 harvest, in an experimental area established with no-tillage since 2010, whose previous history was of grain cultivation, located at UNEPE of annual crops of UTFPR, Campus Dois Vizinhos. The soil of the region is classified as Red Latosol, with the climate defined, according to Köppen, as Cfa (subtropical humid), without defined dry season. The experimental design was a randomized complete block design with subdivided plots and three replications. The main plots included the cultivation of eight systems of winter cover crops under no - tillage (PD), predecessor to maize. The winter cover plants used were: black oats, ryegrass, ryegrass, blue lupine, common vetch, forage turnip, oats + vetch (A + E), oats + vetch + turnip (A + E + N). In the subplots two doses of nitrogen (0 and 180 kg ha-1 of N) were supplied by urea in the main crop (maize). Fabaceae and forage turnip showed higher concentration of N, K, Ca and Mg in dry biomass. Nitrogen fertilization (180 kg N ha1) favored the greatest accumulation of N, Ca and Mg in the dry mass of the cover plants, however, for K, the effect was negative. The supply of 180 kg N ha-1 provided higher N accumulation for the oats, rye, forage turnip and blue lupine systems in relation to the absence of nitrogen fertilization, whereas for the Mg accumulation, the same effect was observed for the consortium A + E + N and forage turnip. The decomposition rate of the consortia was intermediate to that obtained for the isolated cultivation of these species, providing maintenance of 39% of their residues. The common vetch and ryegrass obtained the highest rates of decomposition of the residues, with final maintenance of 30% of the vegetal material. The consortia obtained release of N (55 kg ha-1) similar to the supply provided by common vetch in single crop. Potassium presented as the nutrient with the highest release rate, with final concentration at 120 days, less than 2% for all residues. Among the evaluated nutrients, Ca presented the lowest release rate, followed by P. Consortia, in general, had the highest release rates for N, P, K and Mg.