Effects And Mechanisms Of The Fertilizertion Method Of Ndsa (Nitrogen Depot With Saturated Ammonium) On Increasing Nitrogen Use Efficiency

Nitrogen is the most common and important nutritious element for crop production. However, low nitrogen use efficiency is a world-wide's problem in the present agriculture. On the basis of the very strong regulating ability of ammonium fixation and release in soils, a special fertilization method was established, in which an area saturated with ammonium was formed in soil, named as "NDSA—Nitrogen depot with saturated ammonium". In present studies, the effects of NDSA fertilization method on microbes and enzymes in soil, nitrogen transformation and fate in soil, crop growth, yield and quality were studied. The results obtained from experiments were summarized as follows:1. Effects of NDSA fertilization method on microbes and enzyme activity in soilsSpecial designed container was adopted to observe the influence of NDSA fertilization method on microorganism quantity and urease activity in silt loamy soil. The results indicate that, routine fertilization could obviously increase urease activity in soil. However, in the NDSA fertilization treatments, soil urease activity was increased from the zone of fertilizer site to bulk soil. The activity of urease in the soil zone of 1 cm to fertilization site was nearly totally inhibited during 5 days after NDSA fertilization, and was less than half that of CK even 10d after applying fertilizer. Thus the NDSA fertilization method can effectively inhibite urease activity in fertilizer spot with at least 20 days of valid time, which was favorable to preventing urea from quick degradation in NDSA fertilization site. method can also suppress The reproduction of denitrifying and nitrifying bacteria in the whole incubation stage could be inhibited efficiently by NDSA fertilization, with a similar tendency to urease inhibition. The inhibition of denitrifying and nitrifying bacteria was in favorable to decreasing the loss of soil nitrogen from leaching and denitrification of nitrate. Urea hydrolyzation resulted a significant increase of soil pH in routine fertilization treatment. However, the pH of NDSA fertilization site was 2-3 units lower than that of routine fertilization 10d afterfertilization, which was beneficial to reduce ammonia volatilization.2. Dynamic transformation of nitrogen applied by NDSA fertilization method in soilsDynamics of different soil nitrogen pools after application of nitrogen fertilizer was studied by incubation experiment. The results showed that a high level concentration of NH₄⁺-N in the fertilization site could be maintained by inhibition of NDSA on nitrification of ammonium, and this effect was pronounced by addition of dicyandiamide (DCD). Under routine fertilization conditions,, the processes of urea hydrolyzation and ammonium nitrification, which can be finished in 7d and 21d, respectively, were so fast that the applied nitrogen was nearly completely transformed into nitrate in soil. By the end of incubation, the total amount of ammonium and nitrate in the treatment of routine fertilization was significantly higher than that of NDSA , which should be related to that the mineralization of nitrogen in soil could be induced by the decrease of ammonium concentration due to high nitrification in routine fertilization while ammonium fixation was enhanced by a high ammonium concentration maintenanced by NDSA fertilization, which was more than twice as that in routine treatment. Furthermore, the content of soluble organic nitrogen in the soil of NDSA was significantly higher than that of routine treatment. Therefore, NDSA was helpful to nitrogen preservation and regulation in soil. A recovery rate of nitrogen as high as 81% was obtained in NDSA treatment. However, it could also reached 70% in routine fertilization, which should result from without nitrated leaching in the incubation experiment..3. Volatilization and leaching of nitrogen applied by NDSA fertilization method in soilsThe effects of a new fertilization method-NDSA on the loss of nitrogen from ammonia volatilization and N leaching were studied by the imitated experiments. The results obtained fr...