Abstract:

An important grassland ecosystem management strategy is the application of nitrogen fertilizer; however, the fate of applied nitrogen is highly correlated with risks and benefits associated with the fertilization of grasslands. The fate of nitrogen tracers applied to a typical Inner Mongolia steppe ecosystem has not been studied previously. We examined the fate of 15N-labelled fertilizer in a Leymus chinensis site at the Inner Mongolia Grassland Ecosystem Research Station, Chinese Academy of Sciences. The results showed that after one growing season an average of 31.61% (range from 25.33% to 38.65%) of the applied 15N was recovered in the plant pool. 15N recovered by aboveground and belowground organs significantly increased with increasing nitrogen rates suggesting that nitrogen fertilizer significantly affected the recovery of 15N by plants. About 2.92% (range from 2.58% to 3.16%) of the applied 15N was recovered in the litter, with the percent 15N in the belowground litter significantly higher than in the aboveground litter pool. About 36.16% of the labelled nitrogen was retained in the soil pool, mostly in the 0-40 cm soil layer. 15N retained by the soil increased significantly with increases in the nitrogen application rate. The loss of 15N was about 21.77%-43.38% of the labelled nitrogen. Risk/benefit analysis showed that, under the climatic and soil conditions prevailing during this experiment, fertilizer application rates of 5.25 g N•m-2 and 28 g N•m-2 were associated with high risk/benefit ratios, whereas the 17.5 g N•m-2 fertilizer treatment achieved the lowest risk/benefit ratio among the nitrogen rate treatments. These results provide a reference for future grassland ecosystem management strategies.