Decomposição e emissão de N2O em função da qualidade e quantidade de resíduos culturais na superfície do solo

Abstract

The management of crop residues influence several processes in agriculture, such as soil protection, water dynamics, decomposition, nutrient fluxes and the overall balance of greenhouse gases, mainly N2O. These effects depend on the chemical composition and the initial quantity of the crop residues. Thus, the present work aimed to quantify the decomposition and release of nitrogen (N), phosphor (P) and sulfur (S) of crop residues with different qualities and quantities deposited in the soil surface and N2O emission. The experiment was carried out during 360 days in a Typic Paluedalf, at Department of soil - UFSM, Rio Grande do Sul, Brazil. A randomized complete block design with four replications was used in the experiment. The treatments were composed of vetch (Vicia sativa L.) and wheat (Triticum aestivum) crop residues under quantities equivalent to 3, 6 and 9 Mg ha-1 of dry matter plus a treatment with no crop residues (control). Crop residues were allocated in litter box of 0.16 m2 to evaluate the decomposition. The mulch in 6 and 9 Mg ha-1 treatments were spliced, respectively, in two (low and top) and three layers (low, middle and top) of 3 Mg ha-1 each one. The moisture of the mulch, the DM, carbon, nitrogen, phosphorus and sulfur remaining were evaluated on nine sampling of the residues. The N2O and CO2 fluxes were periodically measured using closed static chambers. In the soil, soil moisture and temperature were continuously determined at depths of 2.5 and 7.5 cm. Soil NH4 + and NO3 - contents were evaluated at some dates N2O emission was performed. There was no interaction between the quality and quantity of C, N, P and S remaining in the residues of vetch and wheat. The quality of the residues had a significant effect on all the evaluation dates with a rapid release of the nutrients. The quantity of residues was not significant for the release of nutrients. The N2O emission was higher for the vetch residue when compared to wheat residue, depending on the initial chemical composition. In contrast, the emission factor was higher for wheat than vetch residues. The quantity had an effect only for the residues of higher quality up to 6 Mg ha- 1. There was no significant difference between the quantities for the wheat residue. The results of this study show that the quality of the residues affects the decomposition and release of nutrients and consequently the N2O emissions. In addition, the quantity of residues affects only the N2O emission when the residue presents high quality.