The objective of this study was to investigate the root growth compensatory effects and cotton yield under drought stress. The results indicate that the root dry weight, boll weight, and cotton yield increased in both the drought-resistant cultivar (CCRI-45) and the drought-sensitive cultivar (CCRI-60). Compensation effects were exhibited under the three-day drought stress treatment at a soil relative water content (SRWC) of 60% and 45% during the seedling stage, and flowering and boll-forming stage over two years. The yield of the drought-resistant cultivar (CCRI-45) was higher than the control, however, following the six-day 45% SRWC drought treatments, the yield of the drought-sensitive cultivar (CCRI-60) was lower than the control. The soluble sugar content, proline content, superoxide dismutase (SOD) activity, and peroxidase (POD) activity of the roots increased under drought stress and then decreased after re-watering, although the values remained higher than those of the controls for a short period. These physiological measures may represent stress reactions and thus may not indicate factors that result in compensation effects. However, catalase (CAT) activity and gibberellic acid (GA) content of the roots decreased under drought stress. After re-watering, the CAT activity and the GA content increased and were significantly higher than those of the controls under the six-day 60% SRWC and 45% SRWC drought treatments. The abscisic acid (ABA) content of the roots increased under drought stress. After re-watering, the ABA content decreased to a lower level under the three and six-day 60% SRWC and 45% SRWC drought treatments than in the controls. According to an analysis of various indicators, the interaction between ABA and GA signals may play an important role in root growth compensatory effects. In summary, the results demonstrate that moderate drought stress is beneficial to root growth and yield. This conclusion is of great significance to improving our understanding of the maximum utilization of limited water resources.

Nitrogen (N) fertilizer plays a vital role in increasing cotton yield, but its excessive application leads to lower yield, lower nitrogen use efficiency (NUE), and environmental pollution. The main objective of this study was to find an effective method to enhance the NUE in cotton production. A two-year field experiment was conducted by using a split plot design with N rates (N0, 0 kg N ha⁻¹; N1, 112.5 kg N ha⁻¹; N2, 225 kg N ha⁻¹, N3, 337.5 kg N ha⁻¹), and cotton cultivars (CRI 69; ZZM 1017; ZZM GD89 and XLZ 30) to evaluate both their individual effect and their interactions on cotton yield and NUE. The results showed that the biomass and N accumulation of four cultivars increased with an increase in N rate, whereas the NUE decreased. Cotton yield increased first and then decreased for CRI 69 and ZZM 1017, while kept increasing from N0 to N3 for ZZM GD89 and XLZ 30. Compared with ZZM GD89 and XLZ 30, CRI 69, and ZZM 1017 showed higher yield, resulted from higher biomass, bolls per plant, and boll weight, especially under low N level. In addition, the CRI 69 and ZZM 1017 had stronger N absorption and transformation capabilities, and showed higher NUE than those of ZZM GD89 and XLZ 30 under the same N rate. The results indicated that CRI 69 and ZZM 1017 show advantages over ZZM GD89 and XLZ 30 in yield, and NUE, especially under low N rate.