Long-Term Grazing and Nitrogen Management Impacted\nMethane Emission Potential and Soil Microbial Community in Grazing\nPastures

Achieving\nsustainable development in livestock agriculture by balancing\nlivestock production, reduction of greenhouse gas (GHG) emissions,\nand effective utilization of nitrogen nutrient has indeed been challenging.\nThis study investigated the long-term effects of continuous cattle\ngrazing, stocking rates, and fertilization regimens on methane (CH<sub>4</sub>) emissions, soil microbial communities, and soil organic\ncarbon (SOC) stocks in Bermudagrass pastures in East Texas, USA. Pastures\nwere subjected to high or low stocking rates for over 50 years, with\nfurther subdivision based on fertilization: nitrogen-based fertilizer\napplication or no fertilizer but with the growth of annual clover.\nSeasonal soil cores (0–60 cm) were collected, and laboratory\nmicrocosm incubation studies revealed unexpectedly high <i>in\nvitro</i> CH<sub>4</sub> emissions in surface soils, particularly\nin the top 0–5 cm soil layer, reaching up to 300 nmol of CH<sub>4</sub> mL<sup>–1</sup>. Higher CH<sub>4</sub> emissions and\nmethanogen abundance, along with lower SOC stocks, were observed in\npastures subjected to high stocking rates compared to those with low\nstocking rates and in clover pastures compared to those with N-fertilized\nryegrass. On the contrary, in low-stocked, N-fertilized annual ryegrass\npastures, methanogen abundance was lowest, CH<sub>4</sub> emissions\nwere negligible, and SOC stocks were highest. Furthermore, animal\nexcreta deposition significantly contributed to increased CH<sub>4</sub> emissions. Prokaryotic and potential methanotrophic taxa, as compared\nto fungi, exhibited greater responsiveness to N-fertilization than\nto cattle stocking treatments with higher levels of methanotrophs\nobserved in pastures subjected to high stocking rates and clover growth.\nThis study suggests that strategic management practices such as optimal\ngrazing and nitrogen management could effectively mitigate CH<sub>4</sub> emissions in grazing lands.