Cotton Genomics and Genetics 2025, Vol.16, No.2, 57-71 http://cropscipublisher.com/index.php/cgg 62 lead to an overly dense cotton canopy and an increase in ineffective leaves. When there is too much water, cotton plants grow vigorously and easily form a closed canopy structure. The internal leaves will prematurely age and turn yellow due to limited light, and the photosynthetic efficiency of the whole plant will decrease. Therefore, appropriate irrigation should ensure a high LAI while preventing the canopy from being overly closed. Practical experience shows that moderate water regulation (such as a small water deficit during the flowering and boll stage) can control the growth of ineffective cotton leaves, improve canopy ventilation and light transmission conditions, and increase the distribution of photosynthetic products to cotton bolls (Zhan et al., 2015). For example, in the drip irrigation cotton field experiment in southern Xinjiang, high-frequency and small-volume irrigation kept the cotton LAI growing steadily without large fluctuations, while the low-frequency irrigation treatment caused the LAI to rise sharply after irrigation and then drop rapidly between irrigations, showing an unbalanced canopy development rhythm (Han et al., 2011). It can be seen that by adjusting the irrigation frequency and lower limit, the growth dynamics of the cotton canopy can be regulated, the appropriate LAI level can be maintained, and a good foundation for yield formation can be laid. Table 1 Effect of irrigation systems and irrigation durations on theaverage number ofbranches per plant (branch .plant -1) (Adopted from Jabr et al., 2020) Irrigation systems Irrigation duration Irrigation systems average Two days Four days Subsurface irrigation 7.33 6.67 6.50 Drip irrigation 4.33 5.00 4.67 LSD= 0.05 0.814 0.717 Irrigation duration average 5.33 5.83 LSD= 0.05 NS 4.3 Flowering and boll formation time The flowering and boll formation process of cotton is also significantly affected by irrigation strategies. Water conditions will change the growth period of cotton: when there is sufficient water, cotton usually blooms and bolls at a normal rhythm; while drought stress may delay or shorten certain growth stages. For example, drought often delays the flowering time because the plant prioritizes survival and delays reproductive transformation when vegetative growth is inhibited and assimilation products are insufficient (Pilon, 2015). When there is severe water shortage, some flower buds will fall off prematurely due to insufficient water and nutrient supply, resulting in a decrease in the number of effective flowers and delayed boll formation. In contrast, appropriate water supply can ensure that cotton blooms on time, the boll formation period is fully extended, and it is conducive to the maturation of seed cotton. Similarly, excessive water supply may also affect the flowering and boll formation dynamics of cotton. Excessive water supply can easily cause excessive vegetative growth of cotton, resulting in delayed flowering and "long and late flowering" phenomena (Wang et al., 2020). This will cause the growth period of cotton fields to be prolonged, the maturity of bolls and fruits in the later period to be inconsistent, and increase the difficulty of harvesting and the risk of reduced yield. Therefore, in order to achieve a reasonable arrangement of cotton flowering and bolling period, it is necessary to regulate it through irrigation. Deficit irrigation has been proven in practice to adjust the growth process: for example, in the Xinjiang experiment, the implementation of mild water control during the flowering period of cotton can slightly shorten the flowering period, make cotton concentrate bolls, improve water use efficiency and do not lose yield (Guo et al., 2015). On the other hand, although continuous and sufficient water supply is conducive to increasing the number of bolls per plant, if irrigation is stopped too late, some late bolls may not fully crack due to water shortage in the later period, affecting yield and quality. Determining the appropriate irrigation termination time is also key. Reeves (2012) suggested that irrigation should be stopped in time after the last effective flowering of cotton to facilitate the maturity and opening of cotton bolls in the later period. In summary, different irrigation strategies change the flowering and bolling pattern of cotton by affecting its growth process. Reasonable irrigation scheduling (including irrigation time and termination period) should ensure that cotton blooms on schedule and produces more and earlier bolls, while avoiding growth delays and bud and boll losses due to water imbalance.
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