In order to research effects of the nitrogen top-dressing levels on carbon-nitrogen metabolism and yield of Desmodium styracifolium, a field experiment was conducted on the research farm of Guangxi University in 2007. Some physiological indexes and yield of D. styracifolium were compared among five nitrogen top-dressing levels (0, 37.5, 75.0, 112.5 and 150.0 kg N · hm-2). Results showed that the nitrogen top-dressing could significantly increase the contents of chlorophyll, soluble protein, sucrose and nitrogen as well as nitrate reducase activity. However, there were no significant differences in most of these indexes under high nitrogen levels. Consistently, there was no significant difference in yield among nitrogen top-dressing levels of 75 kg N · hm-2, 112.5 kg N · hm-2 and 150 kg N · hm-2. Therefore, the optimum nitrogen top-dressing level of D. styracifolium was 75 kg N · hm-2.
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