3.2.1 pH, EC and ESP
Soil pH, EC and ESP of N addition treatments decreased significantly compared with those of non-N addition treatment when N addition rate was more than 90 kg ha-1(P <0.05), and three indexes showed a downward trend with the increase of N addition rates (Fig.4). Compared with the treatment without N addition, soil pH of the N addition treatments with 90-210 kg ha-1 decreased by 0.71-1.19 units, soil EC decreased by 34.4%-67.2%, and soil ESP decreased by 55.7%-65.3%, respectively. In MSSL of L. chinensis , N addition can reduce effectively salinity and alkalinity of 0-20 cm soil.