Cover crops can affect nitrogen fertilization efficiency, soil nitrogen content, and cotton yield. However, the interaction effects of controlled-release nitrogen fertilizers, applied N rate, and cover crops on cotton growth, yield and fiber quality remains unknown, especially in sandy soils with low N content. Soil nitrogen and cotton growth, yield and fiber quality were evaluated as a function of different N rates and N sources in five rotation systems with or without cover crops, over four years. The treatments were: (1) cotton rotation crops (i.e., fallow, single grass, grass + grass, grass + legume and a mixture of cover crops), (2) nitrogen rates (70, 100 and 130 kg N ha⁻¹), and (3) nitrogen sources (urea and controlled-release urea). Under a mixture of cover crops, fiber yields were 12% and 21% higher compared to the single grass and rotation fallow, respectively. Cotton in the fallow rotation required a higher rate of N (130 kg ha⁻¹) than in rotation systems with cover crops (100 kg ha⁻¹), in systems with cover crops to achieve the highest yields. Controlled-release urea reduced the demand for N fertilizer by 30% in the fallow. It also increased the content of soil N by 16% (mean of two seasons). Micronaire and fiber strength were lower with 130 kg ha⁻¹ of N. There is no need to increase nitrogen fertilization in cotton, as long as controlled-release urea and cover crops are employed, preferably mixtures of grasses and legumes.

覆盖作物会影响氮肥施肥效率、土壤氮含量和棉花产量。然而，控释氮肥、施氮量和覆盖作物对棉花生长、产量和纤维品质的交互作用尚不清楚，尤其是在含氮量低的沙质土壤中。土壤氮和棉花的生长、产量和纤维质量作为不同氮肥量和氮源的函数，在有或没有覆盖作物的五个轮作系统中进行了评估，为期四年。处理为：(1) 棉花轮作作物（即休耕、单草、草 + 草、草 + 豆科植物和覆盖作物的混合物），(2) 施氮量（70、100 和 130 kg N ha ^-1)，和 (3) 氮源（尿素和控释尿素）。在混合覆盖作物的情况下，与单草和轮作休耕相比，纤维产量分别高出 12% 和 21%。与覆盖作物的轮作系统（100 kg ha ^-1）相比，休耕轮作中的棉花需要更高的氮肥量（130 kg ha ^-1），在覆盖作物的系统中可获得最高产量。控释尿素使休耕期对氮肥的需求减少了 30%。它还使土壤 N 的含量增加了 16%（两个季节的平均值）。马克隆值和纤维强度较低，为 130 kg ha ^-1 N. 不需要增加棉花中的氮肥，只要使用控释尿素和覆盖作物，最好是草和豆类的混合物。