Effect of nitrogen fertilizer on switchgrass yield, N-use efficiency and residual nitrate nitrogen in Kubuqi Sandland soil

In order to improve the ecological environment of Kubuqi sandland and realize the effective combination of ecological and economic benefits, the warm-season herbaceous bioenergy plant switchgrass (Panicum virgatum) was introduced to Kubuqi sandland. Switchgrass BL-1 was used as the experimental material to study the effect of ammonium sulfate and urea on the yield and nitrogen-use efficiency of this species, and the distribution and accumulation of soil nitrate nitrogen in the 0-40 cm soil layer. The study used a completely randomized block design. Nitrogen fertilization was carried out with four treatments of nitrogen application rate (0, 75, 150, and 225 kg·ha-1) and three duplicates for each treatment. Urea and ammonium sulfate were applied directly to the experimental plots at the seedling stage, tillering stage, and jointing stage, with amount equivalent to 1/5, 2/5, and 2/5 of nitrogen application rate, respectively. The yield of switchgrass and the content of soil nitrate nitrogen were measured at the early flowering stage. The results showed that the application of both urea and ammonium sulfate could significantly increase the yield of switchgrass (P<0.05). The yield, nitrogen uptake, and nitrogen-use efficiency of switchgrass fertilize with ammonium sulfate increased the increase in nitrogen application rate, which first increased and then decreased when urea was applied, and the maximum was at the nitrogen application rate of 150 kg·ha-1. The nitrate nitrogen was mainly distributed at 10-20 cm soil layer and the accumulation of nitrate N increased with the increase of nitrogen application rate in the 0-40 cm soil layer.