Triticeae Genomics and Genetics, 2025, Vol.16, No.4, 156-165 http://cropscipublisher.com/index.php/tgg 157 and it can also slow down plant aging, thereby accelerating the accumulation of dry matter and allowing it to accumulate for a longer time, especially during the important stages of wheat growth (Li et al., 2023). Generally speaking, dry matter accumulation grows in an "S-shaped" pattern. If there is not enough water, wheat will reach the peak of accumulation earlier, but the rate and total amount of accumulation will be reduced (Yan et al., 2022). In addition, the process of transferring dry matter from the nutritional organs such as stems and leaves to the grains is also critical, and this process is also affected by irrigation and nitrogen fertilizer application (Xue et al., 2006). 2.2 Impacts of irrigation frequency on biomass partitioning The frequency of irrigation affects the distribution of dry matter in the wheat plant, such as to the stem, leaves, or ears. More frequent irrigation or more accurate timing of irrigation results in more dry matter being distributed to the ears and grains, which is important for increasing yield. For example, wheat that was irrigated four times during an important developmental stage had more total dry matter and more dry matter distributed to the ears than wheat that was irrigated only once or twice (Pal et al., 2000). When drip or sprinkler irrigation is used, more dry matter is distributed to the leaves and ears, and less to the stem and leaf sheaths, especially during the grain filling period. If water is insufficient, wheat will transfer previously stored nutrients to the grains to make up for the current loss of photosynthesis. 2.3 Developmental stage-specific responses When to irrigate is also important, depending on the developmental stage of the wheat. Irrigation during the jointing, booting, flowering and filling stages can prolong the accumulation time of dry matter and allow more dry matter to be transferred to the grain (Ma et al., 2024). However, if there is a lack of water during the tillering stage or milky stage, the total amount of dry matter and the proportion transferred to the ear will decrease significantly, and the final yield will be greatly affected (Han et al., 2022). Supplemental irrigation from the booting stage to the filling stage can not only increase the dry matter in the nutritional organs and grains, but also reduce the dependence on pre-flowering reserves. Different irrigation times have different effects on wheat of different varieties and in different environments, which will affect yield and water use efficiency together (Moradi et al., 2022). 3 Water Use Efficiency (WUE) in Response to Irrigation Frequency 3.1 Definition and agronomic importance of WUE Water use efficiency (WUE) of wheat refers to the amount of wheat yield or dry matter produced for each unit of water used. The higher the WUE, the more valuable the water is. This indicator is particularly important in water-scarce areas. Because water resources are scarce, improving WUE can help farmers save water while maintaining stable yields (Li et al., 2019b; You et al., 2022). 3.2 Effects of irrigation intervals on WUE How to arrange irrigation and the frequency of irrigation will directly affect WUE. Appropriate irrigation time, such as irrigation at the jointing stage and heading stage, can make wheat grow well and reduce unnecessary water waste, thereby increasing yield and WUE at the same time (Si et al., 2020). For example, in semi-humid areas, if 60 mm of water is applied at the jointing stage and heading stage respectively, relatively high WUE and yield can be obtained (Bian et al., 2016). Increasing the number of irrigations but watering less each time, such as using drip irrigation or micro-spraying, can also improve WUE. This can keep the soil moist and photosynthesis more sustained. However, if irrigation is too frequent or too much water is used, it may waste water, which will reduce WUE and may not necessarily increase yield (Figure 1). In the case of water-saving planting, even if the total yield is slightly reduced, WUE may be higher. This shows that a good balance must be found between yield and water saving (Stallmann et al., 2020). 3.3 Factors influencing WUE dynamics WUE is affected by many factors. For example, drip irrigation and micro-spraying combined with a reasonable irrigation frequency can improve WUE more than traditional irrigation methods, especially when water is insufficient (Hao et al., 2023). Soil type is also important. For example, loam or sandy soil, combined with a low
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