| Livestock dung and herbage litter makes up for the material and energy circulation in grazing ecosystem, which plays an important role in regulating livestock balance and maintaining the ecological productivity of the system. In Longdong Loess Plateau, this is Tan rotational grazing system in typical Steppe. Four stocking rates (no-grazing plot,5.33 sheep/ha,2.67 sheep/ha,8.67 sheep/ha) and two grazing seasons (summer and winter) had been set to analyzed the impacts on the decomposition of livestock dung and herbage litter to provide the scientific basis for the sustainable use of typical grassland. The main results are as follows:1. Responses of sheep dung decomposition to grazingIn summer rotation, the fastest decomposition of dung appeared under 5.33 sheep/ha stocking rate, and the slowest decomposition of dung appeared under 2.67 sheep/ha stocking rate, and the differences were significantly (P<0.05). The average daily decomposition rates of them were 0.632 mg/g and 0.570 mg/g, respectively, In winter rotational grazing, the fastest sheep dung decomposition was under 8.67 sheep/ha grazing rate and the slowest decomposition was under 2.67 sheep/ha, and the average daily rates were 0.622 mg/g and 0.554 mg/g, respectively. The decomposition rate under 2.67 sheep/ha was significantly lower than the decomposition rate under 5.33 sheep/ha and 8.67 sheep/ha grazing (P<0.05).In both summer and winter grazing lands, the sheep dung decomposition rate of organic carbon had the same rule with the decomposition rate of dry matters, and the fastest decomposition rates of nitrogen and phosphorus were under 5.33 sheep/ha.2. Responses of litter decomposition to grazingIn the summer rotational grazing land, the fastest decomposition of litter was under 5.33 sheep/ha grazing rate (average daily rate:0.871 mg/g), and the slowest litter decomposition was at no-grazing plot (average daily rate of 0.734 mg/d), where the decomposition rate of the mixed litter were significant lower than that of other three stocking rates (P< 0.05). However, litter decomposition of the fastest rotational grazing land was 5.33 sheep/ha grazing rate, average daily rate of 0.725 mg/d, and the slowest decomposition of litter was 2.67 sheep/ha, average daily rate of 0.699 mg/d in winter grazing land.The fastest decomposition rates of carbon, nitrogen, phosphorus in summer grazing land were all under 5.33 sheep/ha, but the fastest decomposition rate of carbon was under 8.67 sheep/ha, and the fastest decomposition rate of both nitrogen and phosphorus were under 5.33 sheep/ha in winter grazing land.3. Responses of mixed litter decomposition to grazingIn summer rotational grazing, the fastest decomposition of mix litter was under 5.33 sheep/ha stocking rates and the average daily rate of decomposition was 0.856 mg/g. The slowest decomposition was no-grazing plot and the average daily rate of decomposition was 0.684 mg/g. In winter rotational grazing, the fastest decomposition of mixed litter was under 5.33 sheep/ha stocking rates and the average daily rate of decomposition was 0.796 mg/g, The slowest decomposition was under 2.67 sheep/ha, the average daily rate of decomposition was 0.716 mg/g, of which, the decomposition rates of mixed litter under 2.67 sheep/ha and the other two stocking rates were significantly different (P<0.05).The fastest decomposition rates of carbon, nitrogen and phosphorus in both summer and winter grazing land were under 5.33 sheep/ha.4. The role of stocking rate and the grazing seasons played in sheep and litter decompositionWith stocking rates increasing, the time required for the dung and litter to decompose rized first, and then decreased. The most suitable grazing rate in summer grazing land for the dung decomposition was 6.2 sheep/ha,6.4 sheep/ha for mixed litter decomposition, and 6.3 sheep/ha for litter decomposition; The most suitable grazing rate in winter grazing land for the dung decomposition was 9 sheep/ha,7sheep/ha for mixed litter decomposition, and 7.3 sheep/ha for litter decomposition.Under the grazing rate of 2.67 sheep/ha,5.33 sheep/ha and 8.67 sheep/ha, the decomposition rates of litter in summer grazing land was significantly faster by 18.27% (P<0.05),20.18% (P<0.05),12.53%(P<0.05), than in winter grazing land, and the decomposition rates of mixed litter in summer grazing land was faster by 14.16% (P<0.05),7.58% and 9.26% (P<0.05). The decomposition rates of the dung under the grazing rate of 2.67 sheep/ha and 5.33 sheep/ha were faster by 2.93%,7.64% (P<0.05) and slower by 2.19% than in winter grazing land.5. The turnover rate of the dung and litterIn summer grazing land, it took 25 months for the dung to be 50% decomposed and it took 90 months to be 90% decomposed. The average time for the litter to be 50% decomposed was 17 months in different grazing lands, and 61 months to be 90% decomposed. It took 17 months for the mixed litter to be 50% decomposed, and 64 months to be 90% decomposed.In winter grazing land it took 30 months for the dung to be 50% decomposed, and it took 100 months to be 90% decomposed. The average time for the litter to be 50% decomposed was 20 months in different grazing lands, and 72 months to be 90% decomposed. It took 18 months for the mixed litter to be 50% decomposed.6. The role of species diversity on litter decompositionAfter mixing process for the litter, the number of species in summer grazing land increased by 88.0%, the mass decomposition rate decreased by 1.43%, the return speed of carbon increased by 1.42%, the return speed of nitrogen decreased by 2.79%, the return speed of phosphorus significantly increased by 13.12% (P<0.05). The number of species in winter grazing land increased by 61.7%, the mass decomposition rate, carbon, nitrogen and phosphorus return speed increased by 6.24%,4.48%,16.10% and 7.85% respectively. Among which the mass decomposition rate, nitrogen and phosphorus return rate increased significantly (P<0.05).Proper grazing was positive for the nutrition return of the dung and litter. Summer grazing was more helpful for the decomposition of the dung and litter than winter grazing. A higher diversity of the litter species helped with the nutrition return. |
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