Sheep Excrement Increases Mass of Greenhouse Gases Emissions from Soil Growing Two Forage Crop and Multi-Cutting Reduces Intensity

To explore the effects of multi-cutting and sheep excrement on greenhouse gas (GHG) emissions from grassland ecosystems which simulate grazing livestock to a certain extent, spring wheat ( Triticum aestivum L., var. Yongliang 15) and common vetch ( Vicia sativa L., var. Lanjian 3) were planted in pot experiments in an inland arid region in 2019. Four treatments were conducted with eight replicates: plants without sheep excrement and cutting (CK), plants with multi-cutting (MC), plants with sheep excrement (SE), and plants with multi-cutting and sheep excrement (CE). The results showed that the carbon dioxide (CO 2 ) emission of common vetch with CE significantly was higher than that with MC at the earlier and later branching stages ( p < 0.05). That of spring wheat with CE was significantly higher than that with MC at the later tillering stage ( p < 0.05). Nitrogen oxide (N 2 O) emissions of the two forage crops with SE rose significantly more than those with MC at both stages ( p < 0.05). Methane (CH 4 ) of both forage crops with SE changed from absorption to emission ( p < 0.05). Soil NO 3 − -N content of both forages significantly increased with SE compared with MC ( p < 0.05), while soil NH 4 + -N content did not change significantly. Sheep excrement changed the CH 4 sink into a CH 4 source of the soil growing the two forage crops and increased the emissions of CO 2 and N 2 O, whereas multi-cutting significantly reduced the GHG intensity of forage crops mostly by promoting the growth of the two forage crops. Future studies are suggested to identify the spatiotemporal effects of cutting and sheep excrement on GHG emissions to improve the prediction of future climate impacts from grazing activities.