Grazing mitigates soil GHG emissions while optimizes forage production of annual cereal grasses in an arid saline-alkali land

Abstract

Livestock production faces the challenge of feed shortage due to the escalating demand for livestock products and the continued degradation of grasslands. The cultivation of annual forage crops may be an alternative option in the forthcoming decades. However, the impact of grassland utilization method (grazing vs. mowing) on forage yield and associated soil greenhouse gas (GHG) emissions of annual sown pastures remains uncertain. A 4-year experiment was conducted in a saline-alkali cropland with irrigation of 560 mm yr^-1 in Northwest China. Annual forage crops were rotationally sown to elucidate the impact of grassland utilization methods on forage productivity (hay, crude protein (CP)) and soil GHG (CO₂, N₂O, and CH₄) fluxes, aiming to optimize the trade-off between forage production and soil GHG emissions. Results show that compared to mowing, grazing increased the mean yields of hay and CP by 44.7 % and 50.2 %, respectively; however, grazing had no significant impact on the cumulative soil N₂O emissions and CH₄ uptake but significantly reduced cumulative soil CO₂ emissions during the last two study years. For both grazing and mowing, soil water content was the primary influencing factor of soil N₂O emissions, and soil temperature was the primary influencing factor of soil CH₄ uptakes and CO₂ emissions. Cumulative soil N₂O emissions and CH₄ uptakes had upward trends with the increasing forage hay and CP yields under grazing. Cumulative soil CO₂ emission under mowing had a downward-curving relationship with the hay and CP yields. Overall, compared to mowing, grazing decreased hay and CP yield-scaled soil GHG intensity by 36.3 % and 38.6 % respectively. Grazing presents an effective strategy for optimizing forage production and environmental performance of annual cereal grasses in arid regions.