[Soil nitrogen content and enzyme activities in rhizosphere and non-rhizosphere of summer maize under different nitrogen application rates.]

A field experiment was conducted on fluvo-aquic soil in the North China Plain to study the effects of nitrogen application rate on soil nitrogen contents and enzyme activities in rhizosphere and non-rhizosphere of summer maize. The results showed that the soil enzyme activities under different nitrogen application rates showed similar seasonal patterns. In comparison to no nitrogen ferti-lizer treatment, all nitrogen application treatments significantly increased NO3--N contents in rhizosphere and non-rhizosphere soils, NH4+-N content in rhizosphere soil and the activities of β-N-acetylglucosaminidase, β-glucosidase, β-xylosidase and Cellobiohyrolase. During the whole summer maize growing season, the NO3--N content in non-rhizosphere soil was significantly higher than that in rhizosphere soil. The NH4+-N content in non-rhizosphere soil was also significantly higher than that in rhizosphere soil at filling stage but significantly lower at seedling and maturity stages. Furthermore, soil enzyme activities in rhizosphere soil were significantly higher than those in non-rhizosphere soil. Effect of nitrogen application on soil organic carbon content was not significant. Soil total nitrogen content increased significantly when the nitrogen application rate was 0-180 kg·hm-2 but decreased significantly when the rate was higher than 180 kg·hm-2. Generally, a proper rate of nitrogen fertilizer application could significantly increase soil enzyme activities and total nitrogen content, and then improve soil biochemistry properties.在华北平原潮土上进行田间试验,研究施氮量对夏玉米根际和非根际土壤酶活性及氮含量的影响.结果表明: 不同施氮水平下土壤酶活性均表现出一致的季节性变化趋势.与不施氮处理相比,施氮处理能显著提高根际和非根际土壤硝态氮含量及根际土壤铵态氮含量,显著增强土壤几丁质酶、β-葡萄糖苷酶、纤维素酶和木聚糖酶活性.在整个玉米生育期内,非根际土壤硝态氮含量显著高于根际土壤;非根际土壤铵态氮含量在灌浆期显著高于根际土壤,但在苗期和完熟期则显著低于根际土壤;根际土壤几丁质酶、β-葡萄糖苷酶、纤维素酶和木聚糖酶活性都显著高于非根际土壤.施氮对土壤有机质含量没有显著影响;在0～180 kg·hm-2施氮范围内,施氮可明显增加土壤全氮含量,但当施氮量超过180 kg·hm-2时,土壤全氮含量则明显下降.综上,适量施氮能显著增强土壤酶活性,提高土壤全氮含量,改善土壤生化性质.