| To improve nitrogen utilization efficiency and reduce the nitrate pollution to the groundwater and water eutrophication is one of the hot problems in the field of nitrogen utilization and environmental engineering remediation. Due to the tremendous advantages and potentials of concentrated fertilizer application method, it is expected to be a practical technology to solve the above problems, especially for the concentrated liquid fertilization.This dissertation firstly reviewed the present state of soil nitrogen utilization and nitrogen fertilizer application methods, and then focused on the impacts of nitrogen depot with saturated ammonium fertilization method on soil nitrogen transformation as well as on spatial structure of corn root. Nitrogen release patterns and nitrogen absorption by maize under the condition of nitrogen depot with saturated ammonium fertilization were the major concerned in this study. This paper mainly studied the mechanism and influencing factors of nitrogen depot with saturated ammonium fertilization on maize root morphology during early growth (21 d) and late (90 d) changes in root morphology, nitrogen absorption, in particular, explored the after 90 d maize root formation of the root ball mechanism and influencing factors. Now the main results obtained were ummarized as follows:(1) Under the fertilization of NDSA in the Rhizobox experiments, it found that within 21 d soil pH, soil nitrogen showed grade distribution phenomenon obviously. Ammonium nitrogen content in NDSA fertilization were significantly higher than other treatments, while the nitrate content significantly lower than that of conventional fertilization. Those signified NDSA fertilization restrained the conversion of ammonium to nitrate. At the 6 cm away from fertilization point, the nitrate content increased notably, during the period of nursing experiment, there was little nitrogen transferance to the 12 cm away from fertilization point. The soil urease activity of NDSA fertilization point significantly reduced, thereby prolonged the transformation of urea to ammonium, which helped to reduce the loss of nitrate.(2) Ammonium depot of different nitrogen concentrations appeared that when ammonium depot concentration was 75 g·kg-1, it could well restrained the conversion of nitrogen as well as urease activity, while soil pH remained basically unchanged. When the nitrogen concentration reduced to 15 g·kg-1 and 3 g·kg-1, ammonium depot had a certain inhibitory effect on the conversion of nitrogen and urease activity, but the effect was less than 75 g·kg-1 nitrogen concentration, and pH significantly increased. When the nitrogen concentration was 0.6 g·kg-1 and 0.12 g·kg-1, the inhibitory effect was not significant, and the soil pH increased.(3) Mini-rhizobox experiments were carried out to study the effect of nitrogen depot with saturated ammonium (NDSA) fertilization on the form of corn roots and N uptake. The results indicated that the N uptake of NDSA fertilization was significantly higher than CULTAN, and the NDSA N uptake was higher than other treatments in shoot of corn. Thus it can be seen that NDSA was more efficient in N uptake and nitrogen fertilization utility. The root length, root surface area, root tips, root forks of corn in NDSA were significantly higher than other treatments. The differences of fertilization between treatments in root avgdiam and root volume were not significant.(4) Rhizobox experiments were carried out to study the effect of NDSA fertilization on the spacial distribution of corn roots and N uptake. The results indicated that the NDSA fertilization significantly promoted the growth of the roots and shoots of corn. The fresh mass of roots and shoots increased by 18% and 37%, respectively, compared with that of the conventional fertilization. The corn roots distributed mainly in the soil layer away from the center of NDSA 6 to 8 cm and formed a root ball around the fertilized spot in NDSA treatment. N uptake of corn roots, stems and leaves increased by 43%, 30%, 31% respectively, and apparent N utilization was increased by 15% in NDSA treatment compared with that of the conventional fertilization treatment. The ammonium content of NDSA treatment was two times higher than that of conventional fertilization, while the nitrate decreased to a half, indicating that the NDSA inhibited the transformation of ammonium to nitrate.
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