PSXI-38 Nitrous oxide emissions from excreta of cattle grazed in mixed, single or fertilized pastures of Marandu-grass

Abstract Few options have been found to mitigate nitrous oxide (N2O) emissions in grazing systems, which requires attention, by the researches. The aim of this study was to determine N2O emissions from excreta of cattle grazed in Marandu-grass pastures (Brachiaria brizantha cv. Marandu) with different sources of nitrogen. The experiment consisted of two factors (pasture management and excreta type) in a randomized complete block design, with 5 replicates. The pastures were: 1) CONTROL: Marandu-grass pastures without nitrogen or legume; 2) FERT: Marandu-grass pastures fertilized with nitrogen (150 kg N haArachis pintoi cv. Amarillo). The excreta types were dung (1.6 kg/ treatment) and urine (1.0 L/ treatment) from heifers (353.1 ± 24.1 kg BW) grazing in the pastures. Static chambers were used to evaluate N2O emissions, which were determined by gas chromatography (electron capture detector), and were integrated over time, to calculate the cumulative emissions and the amount of nitrogen lost as N2O. Posteriorly, ANOVA was performed and the Tukey’s test was ran to determine differences among means. Dung emissions of N2O totaled 1151, 579 and 245 µg N-N2O mP = 0.0052). Urine emissions of N2O were 273, 347 and 275 µg N-N2O m2O emission factor differed between excreta type and was 2.2 times greater for dung than for urine (P = 0.038). For dung, the emission factor (EF) varied from 0.15 to 0.83% N-applied and for urine ranged 0.16% N-applied emitted as N2O. The greatest emissions were observed for FERT. Excreta affected N2O emissions, and in all cases, it was much lower than IPCC default Tier 1 emission factor.