Effect Of Nitrogen Application Rate On Forage Productivity And Utilization Of Soil Mineral Nitrogen In Sorghum Hybrid Sudan Grass

The forage productivity, feeding quality and the availability of nitrogen at different nitrogen levels were studied in this research using Sorghum hybrid sudangrass as material under natural field condition. Try to explore the effect of nitrogen on the performance of Sorghum hybrid sudangrass and the absorption, utilization of nitrogen in Sorghum hybrid sudangrass.With an aim to provide some theoretical basis to optimize the management of nitrogen fertilizer and reduce the residue of nitrogen leaching in soil. The main conclusions are as follows:1. The plant height, tiller number, yield and economic benefit were significantly improved under nitrogen fertilizer treatment, but the stem/leaf ratio was rduced. The results showed that fresh yield reached to respectively 149912 and 151878 kg/hm2 in high nitrogen levels (N270 and N360), increased respectively 41.09% and 42.94% compared to control group. The leaf and stem played the same important role in the fresh matter yield; the leaves were more important than the stem to the dry matter yield. The dry mattetr yield of the second harvest reached the highest quantity of 12.35 t/hm2. The best economic benefit reached to 6046 yuan/hm2 in 2008. The total-N content in different tissues of Sorghum hybrid sudangrass was significantly affected under nitrogen fertilizer treatment. The total-N content in whole plant and leaves are significant higher than stem and sheath, The indexes of DMPE,CPPE and NRE all reduced with the increase of the fertilizer-N rates.2. Compared to the stem and sheath, the crude protein (CP) content in leaves significantly increased under different nitrogen levels, the crude ash (CA) content in stem and sheath decreased with the increase of nitrogen levels. In addition, the CF, ADF, NDF and soluble sugar content in different parts of plant increased first and then decreased with the increase of nitrogen levels. With the increase of cutting frequency, the calcium (Ca) and phosphorus (P) conternt in different parts of plant showed a downward trend. The nutrients in whole plant were significantly improved under N180 treatment. The CP, CF and CA in leaves reached a peak value under N270 treatment, while the ADF and NDF reached a peak value under N180 treatment; The CP, CF and CA in stem reached a peak value under N270 treatment, while the ADF and NDF reached a peak value under N180 treatment.3. Fertilizer N rates have significant influence on the distribution of soil nitrogen, and affected NO3--N content in soil profile (0-60 cm). The NO3--N accumulation content was positively correlated with the fertilizer-N rates, especially at the first harvest, nitrogen residue showed a similar change trend as the NO3--N. The NH4+-N was evenly distributed in the soil profile (0-140 cm), and the difference among different nitrogen levels was not significant. The nitrogen residue in soil profile (0-140 cm) was positively correlated with the nitrogen levels.