| Greenhouses almost were closed environment. In greenhouses environmental problems began to emerge as much use of nitrogen fertilizer and the low utilization rate of fertilizer and volatilization N not easy to go out. To optimize fertilizer N efficiency, various attempts have been made to coat or treat N fertilizers with urease inhibitors, nitrification inhibitors, polymers, and elemental S. we designed and conducted laboratory and field experiments to measure air concentrations of NH3, NO2and O3at vegetable fields with the application of urea alone or with coating or with nitrification inhibitor (dicyandiamide, DCD), to study about transformation of N. We studied release of the hydrocarbon in greenhouse.1. With simulation test, the results showed that soil pH and concentration of NH4+-N increased quickly, concentration of NO3--N increased slow by fertilizing different level of fertilization in soil, while soil available Al, Mn, Cu, Zn and Ca decreased sharply with the increasing level of fertilization after one week. The dynamic experiment revealed that the concentrations of5elements of Al, Mn, Cu, Zn and Ca by fertilizing urea in soil were more and more lower with the pH raising, and then they were more and more higher with the pH dropping. The influence on Al was the most important, when pH raising to over7.00, the concentration of exchangeable Al was much lower. The pH influence on Ca was not so considerable. In pH4-8, by formula Y=ax2+bx+c simulating the relationship of concentrations of these pH values and elements, concentrations of these elements were negatively correlated with pH values.2. With simulation test, we studied about change of pH and volatilization of ammonia by fertilizing four different types of urea (general urea, keep water controlled-release urea, Germany slow-release urea, mineral coated urea). The results showed that the fallen rate of pH by Germany slow-release urea was the slowest while the amount of ammonia volatilization was the biggest, in the five weeks the amount was25.6%in alluvial vegetable garden soil,16.7%in red vegetable garden soil,3.0% in tea garden soil,34.4%in Beijing vegetable garden soil. The fallen rate of pH by fertilizing mineral coated urea was the fastest while the amount of ammonia volatilization was the smallest, in the five weeks the amount was8.07%in alluvial vegetable garden soil,5.19%in red vegetable garden soil,0.85%in tea garden soil,13.0%in Beijing vegetable garden soil. Because there was inhibitor (DCD) in Germany slow-release urea, which controlled nitroreaction and the fallen velocity of pH was slow, the amount of ammonia volatilization was great. The mineral coated urea was coated ground phosphate rock and reduced nitrogen release, decreased ammonia volatilization and better than other urea.3. Incubation studies on the effect of dicyandiamide on ammonia volatilization in two different soils such as alkaline soil and acid soil, and on urea-nitrogen transformation and pH value’s change in two different soils show that in these two different soils, pH and ammonia content increased with the elevated temperature, and were higher in treatments with nitrification dicyandiamide than in no-NI control. The amount of ammonia volatilization in alkaline soil was much more than in acid soil, approximately353.18%,618.33%and1080.46%at the temperature of15,25and35℃in the dicyandiamide treatments, respectively. During the whole experiment, the amount of nitrifying nitrogen in soils was declined with the rising tempetature. The amout of ammoniacal nitrogen in soils was increased initially and then reduced, and the time of peak revealed earlier followed with the increased temperature, about one week.4.. With passive sampler techniques NH3, NO2and O3were measured from plastic greenhouse in Changsha suburban, China, over a one and a half month period. By four treatments (T) types (no N fertilizer T1, common urea T2, coated urea T3and common urea with nitrification inhibitor dicyandiamide (DCD) T4, the average concentrations (μg/m3) of NH3, NO2and O3emitted from high to low in order was: T4(31.66)> T2(25.93)> T3(23.52)> T1(7.96), T2(10.99)> T3(8.16)> T4(7.48)> T1(5.20), T2(75.05)> T364.20)> T4(63.85)> T1(49.02), respectively. This implied that photochemical reaction took place and there were accumulated harmful gases after applied N fertilizer in plastic greenhouse. DCD inhibit the conversion of ammonium to nitrate, and increase NH3volatilization and decrease NO2levels. The coated urea decreased the levels of NH3and NO2, and increased nitrogen use efficiency. Significant positive correlations (p<0.01) between temperature and NH3, NO2levels, between soil pH and NH3, NO2levels were found. The O3average concentration in higher latitude of Yinchuan suburban, China, was two times greater than that in Changsha suburban, China. The O3daily concentrations in Yinchuan suburban exceeded160μg/m3(i.e., China’s Grade Ⅰ standard), and the maximal value214.83μg/m3exceeded200μg/m3(i.e., China’s Grade Ⅲ standard).5. Reliable sampling and analysis methods were selected and optimized to meet the requirements of atmospheric nonmethane hydrocarbons measurement using gas chromatography equipped with a mass spectrometry. Method detection limits (MDLs) were found below0.1μg/m3nonethane hydrocarbons. The concentration of NMHC in greenhouse in Changsha suburb was132.53ppb, which were4.44times greater than that of outside. The plant releases much isoprene, and the strong chemical activity of VOCs in greenhouse was more prone to photochemical reaction. The activity of POD outside was greater than that in greenhouse, and fertilization in greenhouse significantly inhibits POD activity in lettuce leaves. Higher POD activity inhibits the growth of plant, so lettuce growth outside is smaller. Especially in second determination, POD activity in greenhouse nitrogen treatment is abnormally low and severely inhibited, while the content of MDA abnormally elevated, far higher than that in other treatments, and lettuce has been obvious environmental stresses, which implied there were accumulated harmful gases and photochemical reaction took place after N fertilizer application in special plastic greenhouse conditions. |
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