Mechanisms And Regulations Of Nitrogen Transformation In Agricultural Soils Amended With Mineral Fertilizers

Mechanisms and regulations of nitrogen transformation in agricultural soils amended with mineral fertilizers were studied in this paper. Results from intensive laboratory experiments and certain supplemental pot experiments were as follows. (1) Microbial activities in nitrogen transformation were strongly controlled by soil types. Activities of ammonification, urease, ammonia-oxidation, nitrite- oxidation or dissimilatory nitrate reductase (DNR) in different soils were best related to the contents of organic matters, contents of clay, and values of pH in different soils. Moreover, it was very interesting that the activities of DNR in Red earth and Yellow-mud soil were enhanced only by the addition of formate, while the activity of DNR in Fluvo-aquic soil could be enhanced by addition of formate, acetate, glucose or arginine. (2) Rates of urea hydrolysis were different in different soils. For most soils, urea was almost completely hydrolyzed within 32 hrs, but the rate of urea hydrolysis was retarded when concentration of urea was high. Although the kinetic constants of urease were different under different temperatures or different incubation times, soil urea hydrolysis took place in the form of low affinity reaction. 2 ~WL1*t ~ ~ ?ABSTRACT (3) There were notable nitrite accumulations in the process of soil nitrification. Nitrapyrin and sodium azide could effectively inhibit the nitrite accumulation in soil. Ammonium-N levels, soil acidity, and stability of nitrite in soil were the major causes of nitrite accumulation. Acid soil had no nitrite accumulation at all ammonium-N levels, while alkaline or calcareous soils had significant nitrite accumulation, which was increased with the increase of ammonium-N rates. In buffered soil slurries with aeration, the concentrations of nitrite and nitrate were increased with elevated pH. Another reason of nitride accumulation in alkaline soils was the high stability of nitrite in those soils. (4) 7 chemical compounds and extracts from 7 plants had little effect on urea hydrolysis, but significantly had retarded the nitrification in 3 soils with different properties for 20 days. (5) Scenedesinus ob/iquus, a green algae, was able to uptake the NO~ 桸 and NHrN in water. Both the NO~桸 uptake and the NH4桸 uptake could be described by Michaelis-Menten kinetic model. (6) Inoculation of Scenedesnius obliquus in flooded-water at early periods after fertilizer application could significantly fix the NH4桸 and NO~桸 in flooded-water.