2.2 Experimental design
A grassland was established for implementing grazing in 1992. Four methods (GE, continuous grazing (CG), mowing and grazing (MG), and RG) were conducted in 2001, with each method being replicated thrice. GE was implemented by deploying fences to avoid disturbance; CG was performed from April to November each year; MG involved annual mowing in mid-June (with a stubble height of 3 cm) and subsequent grazing till the end of the growing season (November); RG involved grazing for 7 to 10 d per month in each subplot from April to November, with the grass height being maintained at approximately 3 cm after each grazing session. The grazing livestock were 2 to 3 year-old healthy sheep, with a stocking rate of 10 sheep units / hm2. All grazing methods were performed using 60 kg·ha-1 nitrogen fertiliser (urea) and 300 kg·ha-1 calcium-magnesium-phosphate fertiliser (superphosphate), which were added in late June and mid-to-late October, respectively (H. Sun, 2014).