Study On Nitrogen Utilization And Losses In The Seed Production Of Artificial Leymus Chinensis Grassland

Leymus chinensis grassland is one of the best pasture types and an important ecological shelter in northern China. Howerver, it is rapidly degraded due to the over-utilization and other factors in recent years, which further severely blocks both the healty and stable development of animal husbandry industry and ecological construction. Therefore, improving grassland production performance of Leymus chinensis is required for animal husbandry development and ecological protection. Nitrogen application has been generally considered to be one of the most important methods for improving the grassland production. High nitrogen use efficiency not only can improve the yield, but also reduce the environmental pollution caused by nitrogen losses. While ther is little known about nitrogen utilization and losses in Leymus chinensis grassland, this project aims to use15N isotope tracer technique combined with lysimeter method to evaluate the nitrogen utilization and losses status in Leymus chinensis seed. Therefore, the project can provide a theoretical and practical basic for improving nitrogen use efficiency and reducing risk:benfit ratio in Leymus chinensis grassland. Experimental design using randomized block-split-plot experimental design methods, the primary processing time for nitrogen (autumn fruit nutrition during and after spring turning green), split-plot for nitrogen levels (Okg/ha, and120kg/ha, and240kg/ha). Results are as follows:1.The Fall and Spring nitrogen application can improve seed yield, but autumn effects of nitrogen application on seed yield increase significantly the following year. Improve seed yield in autumn by raising spike number per square merter and seed number per spike and thousand seeds weight, and spring application of nitrogen can improve Leymus chinensis seed number per spike and thousand seeds weight,has no effect on spike number per square merter.2.The N derived from fertilizer of grain is higher than hay and root,and above-round is higher than underground.15N labeled nitrogen fertilizer utilization sort for240kg/ha nitrogen fertilizer in the spring (44.68%), the240kg/ha of nitrogen in the antumn (36.02%), the120kg/ha of nitrogen in the spring (28.24%), the120kg/ha of nitrogen in the antumn (22.88%), although it is possible to significantly increase the seed yield in autumn, but there is a low nitrogen fertilizer in the autumn of hay production. Despite spring application of nitrogen fertilizer on seed yield of no nitrogen fertilizer in the autumn, but nitrogen fertilizer in spring to be able to significantly increase the production of hay. Compared with the nitrogen in the antumn, spring application of nitrogen is more conducive to improve nitrogen use efficiency of leymus. Autumn nitrogen can significantly increase the seed yield,but production of hay is lower than spring,by contrast,Spring nitrogen can significantly the production of hay.3. Under different nitrogen treatments, soil nitrogen fertilizer residues in45.92%-67.92%, and exist in0-60cm distribution in the soil.with increasing soil depth, gradually reduce the residual rate, the rate of residual nitrogen in the antumn is significantly higher than in the spring. Nitrogen fertilizer under different nitrogen treatments and N2O NH3volatilization rate of1.00%-3.21%. Unknown loss of nitrogen fertilizer by means of5.91%-10.23%.In this experiment,because the low rainfall in experiment area is not enough to make soil residual nitrogen leaching effect,so the nitrogen leaching losses are0.4. Under different nitrogen treatments of risk:benfit ratio is greater than1, indicating nitrogen loss risk is greater than utilization. Minimum risk:benfit ratio is nitrogen application of high levels(240kg/ha) in the spring. Spring application of nitrogen on average significantly lower than the autumn for risk:benfit ratio. The suggests that in the seed production of nitrogen fertilizer management,although the antumn nitrogen application can increase the seed yield,but also increase the risk of nitrogen losses.How can improve the seed yield and reduce the nitrogen loss of nitrogen, still need to do further research.