中文摘要：

以美棉33B为材料，研究了施氮量对棉田土壤养分和酶活性的影响，为精确农业的精确施肥及棉花产量和品质改善提供理论依据。结果表明，合理施用氮肥能提高0～20cm关键生育期土壤速效养分和酶活性；速效养分质量分数分布特征为苗期和开花期升高、花铃期降低，吐絮期开始回升的趋势。施氮量主要影响0～20cm土壤脲酶和20～40cm剖面磷酸酶时空分布；脲酶活性高值出现比速效养分质量分数最高值早一个生育时期；就某一生育时期而言，脲酶活性与土壤碱解氮、速效磷、速效钾呈极显著的正相关；土壤磷酸酶与速效磷存在显著或板显著相关。整个生育期内土壤速效钾与酶活性呈显著或极显著正相关；脲酶活性高值出现比速效养分质量分数最高值早一个生育时期，为脲酶作为更灵敏的指标提供了有力证据。

英文摘要：

The effects of nitrogen fertilizer rates on soil available nutrients and soil enzymatic activity variation characteristics in cotton field were studied in this paper. The results showed that nitrogen fertilizer rates could improve soil available nutrients and enzyme content at topsoil （0-20 cm） layer. The soil avail- able nutrients contents increased gradually from seedling to blooming stage, decreased dramatically at bollforming stage, and then increased gradually at opening stage. The profile distribution of enzymatic activity of soil： nitrogen fertilizer mainly affected urease distribution in topsoil layer, and phosphatase in 20 to 40 cm layer. Through correlation analysis： maximum of alkaline nitrogen content appeared later a growth stage than urease activity, but in all the variations trend of soil alkaline nitrogen was similar with urease. In a growth stage, the contents of soil organic matter, nitrogen, phosphorus and potassium had significantly positive correlation with the urease activity. The significant or very significant correlation existed between available phosphorus and phosphatase, enzymatic activity and available potassium. Nitrogen-free treatment： urease and phosphatase activity at seedling stage was significantly higher than others stages.