Decomposição e liberação de nutrientes da palhada de azevém (Lolium multiflorum) submetida a diferentes locais de deposição

Abstract

Although the effects of grazing on decomposition have been demonstrated in several studies within crop-livestock integration systems (ILP), few have examined the roles of site conditions as intermediate factors, ie effects on soil conditions, decomposition. Usually, the effects of previous grazing are evaluated, in which there is a change in the structure and composition of the forage plant. The objective of this work was to evaluate the decomposition dynamics of ryegrass residues, as well as the rate of nutrient release, under different conditions of decomposition sites, where residues of ryegrass plants were placed with presence or not of animals. In order to do so, we used the methodology of using litter bags placed in the field in an experiment with a randomized block design in a factorial scheme where Factor A was the presence of animals at two levels: and Without Animals (SA). Factor B were the Days After Deposition (DAD) and were composed of seven litter collection dates. The dry matter (DM) decomposition rates of ryegrass residues, as well as the rate of nutrient release, were estimated by adjusting for non-linear regression models. The kinetics of the process of decomposition of ryegrass residues deposited in areas with presence of animals was faster than when compared to residues that were not on the presence of animals, that is, there was a greater amount of residual residues where there were no animals. The half-life time was higher at the site with animals due to the presence of more readily available material, the increase of this compartment is related to the increase in quantity and diversity of the microbial biomass, where the microorganisms started to access parts of the plant that without the animal presence was not possible. As for nitrogen contents, nutrient accumulation was observed in the non-animal site, because there was immobilization of N due to a smaller amount of microorganisms to participate in the decomposition process, requiring a higher retention of N to get the work done. As for phosphorus, there was no effect of the presence of animals on the phosphorus release rates between the deposition sites, but it was possible to observe a trend of greater retention or immobilization at the non-grazed site, same thing observed for potassium; concentration of this nutrient was influenced by the presence of animals. Finally, it was observed that the presence of animals changes the decomposition sites, mainly influencing the soil biological community, which will have a direct effect on straw decomposition and nutrient release, altering the process as deeply as changes caused by a grazing, where there are changes in the structure of the plant.