Supplemental irrigation based on soil moisture levels at different growth stages of winter wheat can improve photosynthesis and grain yield. By measuring soil moisture in various layers, researchers found that irrigation at specific stages led to higher photosynthesis rates and better grain quality. Treatments with optimal irrigation amounts showed increased sucrose and starch content in leaves and grains, resulting in higher grain yield and water use efficiency. Overall, the study suggests that adjusting irrigation based on soil moisture levels can help achieve higher yields and better water conservation in winter wheat production.