2.3 Sampling and measurement methods
According to the cutting habits of local L. chinensis as forage, it is usually harvested in early September every year. Thus, the plant and soil samples of the L. chinensis were collected in early September in 2018. The sampling was carried out at random sites with a sampling size of 0.5 by 0.5m, with three replications within each plot. The plant samples were cut the shoot at ground level in a sampling size zone, put them into the oven and killed green at 105℃ for 2 h, oven dried at 65℃ for 12 h, and then grated them less than 1mm. The soil samples were randomly taken three soil cores (diameter of 40 mm) at 0 to 20 cm depth within each plot, then mixed well and air dried, passed through a 2-mm sieve and then measured for the concentrations of soil salinity, nutrients and soil enzyme activities.
The protein content of L. chinensis was determined by continuous flow analyzer (SKALAR SAN++), the fat content was determined by soxhlet extraction method, the coarse fiber content was determined by acid-base washing method, the ash content was determined by using burning method of high temperature at 550±20℃, and the concentrations of K+, Na+, Ca2+ and Mg2+ were determined by ICPS-7500 plasma emission spectrometer after the plant samples were combined digestion by nitric acid and perchloric acid (Bao, 2000),
Soil salinity and nutrients were measured by using conventional methods, and the specific methods were the same as those in our previous study (Huang et al., 2015). The related soil enzyme activities were determined by using the method of Guan et al . (1986), soil samples were cultured in a constant temperature incubator at 37 ℃ for 24 h, and then soil urease activity was determined by sodium hypochlorite phenol colorimetry, soil catalase activity was determined by potassium permanganate titration, and soil sucrase activity was determined by 3, 5-Dinitrosalicylic acid colorimetry.