Cotton Genomics and Genetics 2025, Vol.16, No.2, 57-71 http://cropscipublisher.com/index.php/cgg 61 irrigation came into being. Precision irrigation relies on modern sensing, control and information technology to monitor soil moisture and crop status in real time and automatically irrigate on demand. Through soil moisture sensors, crop water stress detection (such as leaf temperature, canopy images) and remote control systems, cotton fields can achieve precise water control at different locations and times. A two-year field study by O'Shaughnessy et al. (2023) proved that the automatic control irrigation system based on sensor feedback can maintain a yield equivalent to full irrigation at a cotton water replenishment level of 75%, while saving 16%-20% water, and the automatic control effect is equivalent to manual monitoring. The introduction of internet of things (IoT) technology has made precision irrigation of cotton fields a reality. Through wireless sensor networks and intelligent algorithms, irrigation time and dosage can be dynamically determined to achieve "water supply on demand" (Faruk and Debnath, 2021). Precision irrigation upgrades traditional experience management to digital precision management, and is one of the future development directions of cotton irrigation. 4 Effects of Irrigation Strategies on Cotton Growth Parameters 4.1 Root development and plant height Irrigation level directly affects cotton root morphology and aboveground growth. Appropriate water supply promotes the growth of cotton roots to the deep layer, thereby expanding the volume of water and nutrient absorption; on the contrary, excessive drought will force the root growth to be restricted or even cause root dehydration and necrosis, and excessive moisture will reduce root activity due to soil hypoxia (Luo et al., 2016). Under deficit irrigation conditions, cotton plants often adapt to water shortage by increasing the root-to-crown ratio, that is, the root system allocates more biomass to explore water sources, while the aboveground growth is inhibited to a certain extent. Wang (2008) found that moderate water deficit (50%-60% of field water holding capacity) at all growth stages can stimulate cotton roots to go deeper and better absorb deep residual water, while inhibiting excessive stem and leaf growth and achieving root-crown coordination. Li et al. (2020) found that severe water shortage at any growth stage significantly inhibited plant height and stem diameter. However, mild deficit (irrigation volume of 90% of full water) has no significant effect on plant height. At the same time, the root system shows higher root length density and root hair volume under moderate drought (Guo et al., 2023). On the contrary, under excessive irrigation conditions, due to the long-term wetness of the surface soil, the cotton root system tends to be shallowly distributed, and the shallow rooting reduces the plant's stress resistance. In addition, excessive moisture will reduce the number of root fibrous roots and reduce the root absorption efficiency. Wang et al. (2007) compared the cotton root systems of different irrigation strategies and found that strictly controlling the lower limit of irrigation under drip irrigation under film can significantly affect the root morphology: the average root diameter of the root system increased and the total root length decreased in the treatment of lower irrigation limit (more drought), while the root system was finer and denser but shallowly distributed in the treatment of higher lower limit (wet). In summary, the irrigation strategy regulates the distribution of cotton roots and the aboveground part through the soil water environment: reasonable water stress is conducive to creating "deep roots and strong plants", while excessive water supply is easy to lead to "shallow roots and vigorous growth", which in turn affects the stress resistance and stable yield of cotton. 4.2 Leaf area index and canopy development Leaf Area Index (LAI) is an important indicator for measuring cotton canopy growth, reflecting the total leaf area per unit land area. When irrigation is sufficient, cotton can maintain a high LAI and form a dense canopy, thereby intercepting more light energy for photosynthesis; when water is insufficient, leaf growth is inhibited, LAI decreases, and plants may shed leaves to reduce transpiration during severe drought. Studies have shown that cotton LAI varies significantly under different irrigation regimes (Table 1). Field trial data from Papastylianou and Argyrokastritis (2014) showed that compared with full irrigation of two cotton varieties ("Julia" and "Zoi"), LAI under deficit irrigation decreased by 23% and 38%, respectively. The LAI of cotton treated with mild water deficit (irrigation lower limit 75% field capacity) was only slightly lower than that of full irrigation, while severe water deficit (lower limit 50%) resulted in significantly smaller leaves and fewer leaves (Wu et al., 2023). The reduction of LAI caused by water deficit is also accompanied by changes in leaf function, such as decreased stomatal conductance and reduced net photosynthetic rate (Pettigrew, 2004). On the other hand, excessive irrigation may
RkJQdWJsaXNoZXIy MjQ4ODYzNA==