In most sandy soils with low organic matter content, nitrogen fertilizers are often applied to achieve desired crop yields, which may negatively affect microbial activity in the soil. We hypothesize that cover crops can mitigate the negative effects and balance the system via increased supply of carbon. The objective, therefore, was to evaluate the effect of cover crops (fallow, one grass species, two grass species, one grass species and legumes, and a mixture of three cover crops), nitrogen doses (70, 100, and 130 kg ha⁻¹), and nitrogen sources (conventional urea and controlled-release urea) on soil microbial activity, glomalin content, and relationship of these parameters of soil quality with cotton fiber yield. Grass systems increased the soil dry matter supply. The carbon of the microbial biomass was 117% higher in the mixture and soil respiration and the metabolic quotient was 128% and 372% higher in the mixture compared to fallow. Fluorescein diacetate hydrolysis was (averaging two-year data) 60% higher in mixed cover crop systems than with fallow. Carbon from microbial biomass (grass + legume system) and glomalin content (all systems) were lower with the highest dose of N. Controlled-release urea can mitigate the negative effects of high nitrogen doses in environments with low dry matter input (as noted for enzyme β-glucosidase). Microbial biomass carbon, β-glucosidase, and qCO₂ were the principal indicators of soil quality and were highly correlated with cotton yield. We recommend the use of a diversity of cover crops, moderate nitrogen doses, and controlled-release urea activate microbial and glomalin activity in sandy soil.

在大多数有机物含量低的沙质土壤中，经常使用氮肥以达到所需的农作物产量，这可能会对土壤中的微生物活性产生不利影响。我们假设覆盖作物可以减轻负面影响，并通过增加碳供应来平衡系统。因此，目的是评估覆盖作物（休耕，一种草种，两种草种，一种草种和豆类以及三种覆盖作物的混合物），氮素剂量（70、100和130千克公顷）的影响。^-1）和氮源（常规尿素和控释尿素）对土壤微生物活性，gloomalin含量以及土壤质量这些参数与棉纤维产量之间关系的影响。草类系统增加了土壤干物质的供应。与休耕相比，微生物生物量的碳在混合物和土壤呼吸中高出117％，代谢商在混合物中高出128％和372％。与休耕相比，混合覆盖农作物系统中的二乙酸荧光素水解（平均两年数据）高60％。氮含量最高时，微生物生物量（草+豆类系统）和gloomalin含量（所有系统）中的碳较低。控释尿素可减轻干物质输入量低的环境中高氮剂量的负面影响（如β-葡萄糖苷酶）。微生物生物量碳₂是土壤质量的主要指标，并且与棉花产量高度相关。我们建议使用多种覆盖作物，适度的氮素剂量和控释尿素来活化沙质土壤中的微生物和gloomalin活性。