Effect Of Applying Urea Fertilizer On Community Standing Crops And Composition Of Mowing Grassland In Steppe Of Stipa Grandis

In the grassland region of Inner Mongolia, herdsmen had always mowed tall grass in autumn and prepared to feed them to livestock in winter. The grassland had been degenerate more and more because of being mowed year by year. Considered of these problems, the paper studied and analyzed the effect of applying urea fertilizer to mowing grassland on the standing crops, species composition, community structure and nutrient elements content of main populations in Stipa grandis grassland of typical steppe. The results showed:1. For the plots mowed once a year, their community standing crops after adding N was higher than that of control plots, not only in the same year, but the plots with higher gradient N3 (140 kg·hm-2),N4 (170 kg·hm-2)) also had significantly higher productivity in the next year after adding N. For the plots mowed twice a year, only with highest gradient (N4), could have significantly higher standing crops compared to control plots. As far as no mowing plots were concerned, N Addition had no significant effect on them, although the addition worked somewhat.2. Community species diversity of the two mowing systems increased fluctuate with the adding gradients increased except for no mowing system. As for evenness, they all appeared descended with the adding gradient increased on the whole.3. For the three main populations, the paper had considered two aspects being affected by adding N:their standing crops and nitrogen content. Firstly, after adding N Stipa grandis and Leymus chinensis showed equal and super compensation on standing crops in control plot and plot mowed once a year, while in plot mowed twice a year they were deficient compensation; while Cleistogenes squarrosa showed opposite rules, their standing crops were equal compensated in control plot, but super compensated in plots being mowed after adding N; secondly, for the nitrogen content, which in Stipa grandis and Leymus chinensis were increased with the adding gradients whether in the mowing once a year plots or in no mowing plots.4. But for Cleistogenes squarrosa, this phenomenon only could be found in the plots mowed once a year, while in no mowing plots, nitrogen content reached highest with N2 (110Kg/hm2) gradient, and after that, it maintained the level.5. Urea fertilizer addition not only could ensure productivity of grassland mowed once a year, but improved the grassland quality in some degree. The effect of N4 gradient on grassland was most positively.