N2O emission factors from sheep excrement in grass pasture systems with or without the inclusion of supplementation or legumes

Abstract

In grazing sheep systems, excreta is a significant source of nitrous oxide (N₂O) emission. The quantification of emission factors (EF) is essential due to limited data in the literature. Supplementation and the inclusion of legumes have been studied as mitigation strategies in temperate climate systems. The objective of this work was to evaluate the N₂O emission factors from sheep excreta in grass grazing systems, with or without the inclusion of legumes and supplementation. The experiment followed a randomized block design with six treatments and four replicates, using urine (U) and feces (F) samples from sheep submitted to three feeding systems: Italian ryegrass overseeded in Tifton (G), ryegrass overseeded in Tifton with energetic supplementation (G+S) and ryegrass and legumes overseeded in Tifton (L). The treatments were: UG, UG+S, UL, FG, FG+S, and FL. Greenhouse gases were obtained from collections using the static chamber methodology, consisting of a base and a galvanized steel chamber. Air samples were collected in four separate time points. The nitrous oxide emission factor (EF) was calculated based on the difference between the cumulative emissions from the treatment and the control, divided by the amount of nitrogen applied. The data were subjected to a normality test and then followed by analysis of variance and Tukey test at a 5% significance level. No significant differences were observed among the treatments, with EF (%) means of 4.53 (UG+S), 4.06 (UL), 3.34 (UG), 3.04 (FG+S), 2.37 (FL), and 2.32 (FG). Dietary changes did not cause sufficient modifications in the excreta to alter the emission factors. We can conclude that the nitrous oxide emission factors from sheep excreta are not influenced by the presence of legumes or supplementation in temperate grass pasture systems.