The Effects Of Neem Seeds Extracts On The Transformation Of Chemical Nitrogen Fertilizer In Different Solis

A series of laboratory experiments pot experiment and microorganism incubation experiment were conducted to study the effects of neem ( Melia azedarach L. ) seeds extracts (NAS) with different technologies on the transformation of chemical nitrogen fertilizer in soils, the biomass and yield of maize and dry rice, and the efficiency of chemical nitrogen fertilizer. The laboratory experiments were conducted in White Soil, Yellow- brown soil, fluvo-aquic soil and seriozem soil to study effects of NAS on the transformation of chemical nitrogen fertilizer in soils. The results showed that NAS could reduce the nitrification rate, lower the N03-N content, and increase the content of total N and organic matter of soil. During the incubation, NAS was effective in promoting the immobilization of inorganic nitrogen in the former while improving the mineralization of organic nitrogen in the later. A microorganism incubation experiment was conducted in the liquid culture medium to study the mechanism of inhibited nitrification by NASa.The results showed that NASa could inhibit nitrification of Nitrobacteria, and the effect of inhibition had a direct relation to content of NASa. Pot experiments conducted in garden-soil showed that NASd NASb-30% could increase the yield of maize and rice cultivated on upland soil, and improve the nitrogen use efficiency of the two crops. NASd~ NASb-30% and NASa-30% could increase the crude protein content of the rice. A pot experiment conducted in paddy soil collected from Yixing county,Jiangsu province showed that NAS was more effective in reducing the nitrification rate, increasing the content of total N and organic matter of soil, and promoting the residual use efficiency of nitrogen fertilizer compared with those in DCD treatment. NAS also could increase the nitrogen use efficiency of the rice and both NASb-15% and NASd-15% were more effective than DCD and other extarcts. The mechanisms of NAS in increasing the N use efficiency might partly be the inhibition of nitrification by NAS, the rapid incorpration of ammoniam-N into soil biomass and their later release of immobilized N.