The Effects Of Urease/Nitrification Inhibitors On The Nitrogen Flow In Paddy Ecosystem

Fertilization plays a vital role in rice yields. Excess nitrogen applied to paddy ecosystem raises the yield less, and makes nitrogen loss much, then resulted in the low efficiency in rice production and environment pollution. Urea is the most commonly nitrogen fertilizers used in China, if utilization of urea is improved, the nitrogen pollution from the paddy source could be controlled. Considering biochemical conversion process of nitrogen in the soil, using inhibitors as adjustor is an effect measure to achieve high efficient utilization of urea nitrogen and to reduce environmental pollution in paddy ecosystem.A pot cultivation in this thesis was used to research the effects of urease inhibitor HQ, nitrification inhibitor DCD and their combined application on the flow mechanism of nitrogen in paddy ecosystem with urea and without urea. The ammonium, nitrite, nitrate, total nitrogen concentration, and pH of the soil leaching water in root zone, the SPAD reading of top three leaves and the upmost leaf, and biomass, nitrogen concentration of rice plant, residual nitrogen concentration of soil after harvest were measured. The balance of nitrogen flows in paddy ecosystem was calculated based on the above measured data. The main conclusions from this paper are listed as following:With the addition of inhibitors, the concentration of ammonium and total nitrogen of leaching water in root zone in paddy ecosystem were increasd, and the concentration of nitrite and nitrate of leaching water in root zone were reduced. Meanwhile, the ratio of ammonium nitrogen/total nitrogen in soil leaching water increased, and the ratio of nitrate nitrogen/nitrogen decreased. The effect of inhibitors applied in paddy with urea was better than them applied in paddy without urea, and it was also concluded that the combined application of HQ and DCD was more effective than single using one of them. The pH of leaching water was correlated with the concentration of nitrate concentration negatively, but ammonium nitrogen positively.With the addition of inhibitors, the SPAD reading from top three leaves and the upmost leaf were significantly improved, and SPAD value descreasing caused by aging of leaves were effectively prevented. Plant height, spike number, biomass and production were also increased because of addition of inhibitors. The same conclusions as above were obtained:the effect of inhibitors applied in paddy with urea was better than them applied in paddy without urea, and it was also concluded that the combined application of HQ and DCD was more effective than single using one of them.Whether or not applied urea, the addition of inhibitors could increase the amount of nitrogen in organs of rice, and combined addition of HQ and DCD could significantly increase the total nitrogen of root, stem, leaf, and spike of plant simultaneously. There were no influences on the nitrogen concentration in soil after harvest caused by applied inhibitors without urea, but application of inhibitors with urea could help to maintain the nitrogen concentration of the 0-25cm soil layer, which was beneficial to the efficient absorption of nutrients.There have been a certain influences on nitrogen balance in paddy ecosystem by addition of inhibitors. Because of inhibitors, the absorption of nitrogen was improved, and the concentration of nitrogen in leaching water and residual nitrogen in soil slightly increased. But with the inhibitors addition, the "other" nitrogen in gaseous loss primarily was reduced significantly.