Nitrogen application: an important measure of restraining vegetation degradation in salinealkaline grasslands in northeast China

摘要

Songnen plain is the most typical area of saline sodic soils extensively distributed in northeast China. Soil salinization and over-grazing resulted in severe degradation of the grassland in the region, and the yield of L. chinensis decreased significantly. We found that nitrogen nutrition was very deficient in saline-sodic grasslands according to field sampling data, in general, total nitrogen in soil was below 1.0%, and available nitrogen content was between 10 mg·kg-1 and 30 mg·kg-1. Nitrogen has become a major factor limiting plant growth. From 2006 to 2008, nitrogen fertilizers application was performed in saline-sodic grasslands which vegetation is mainly Leymus chinensis, the results showed that, in the grassland of soil pH 9.5, plant height of Leymus chinensis increased over 0.5 times when 30-210 kgN·ha-1 was applied than that of no fertilization, the population density increased 0.22-1.05 times than that of no fertilization, and dry weight of aboveground biomass reached from 2.9 t·ha-1 to 6.8 t·ha-1, increasing 0.66-2.73 times than that of no fertilization (1.79 t·ha-1); the growth rate of Leymus chinensis was the highest at 210 kgN·ha-1 applied, the biomass increased 222.2 kg·ha-1 per day; NUE was the highest while 90 kgN·ha-1 was applied, and it may reach 51.6 kg hay·kg-1N. Nitrogen application can significantly improve biomass and population density of Leymus chinensis, furthermore, enhance the productivity of grassland and accelerate vegetation recovery. The optimum of nitrogen application is 90 kgN·ha-1. Nitrogen application is an important measure of restraining vegetation degradation in saline-sodic grassland in northeast China.