Effects of the Drip Irrigation Layout and Dripper Flow Rate on Soil Water, Salt Distribution, and Cotton Growth

The drip irrigation layout and dripper flow rate impact the soil water and salt distribution, leading to uneven growth in the middle and side rows of cotton within a mulched drip irrigation system. Consequently, it is crucial to analyze how these factors influence soil water, salt distribution, and cotton growth. This study examined three drip tape layouts (L1: in the middle of a narrow row; L2: drip tapes in the middle and on both sides of a narrow row; L3: on the left side of the narrow row) and three dripper flow rates (Q1: 2.4 L/h, Q2: 3.2 L/h, Q3: 3.6 L/h). The findings indicated that the Q2L2 combination provided the best soil water and salt distribution in the 0–60 cm root zone, with a 41.68% increase in water content, a 38.49% increase in soil water storage, and a 50.42% reduction in relative salinity compared to other treatments. Plant height, stem diameter, and leaf area index under Q2L2 were significantly higher than the other treatments (p<0.05), dry matter accumulation peaked during the flowering and boll stage, with the highest proportion in the bolls, and cotton yield (7,228.31 kg/ha) and water use efficiency [15.27 kg/(ha·mm)] were also the highest. A structural equation model revealed that drip irrigation layout and dripper flow rate indirectly influenced cotton growth and yield by regulating the soil water and salt environment. Using the entropy weight and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) models, we assessed four indices: relative change in soil salinity, water use efficiency, dry matter accumulation, and cotton yield. The Q2L2 treatment had the highest evaluation index, with a closeness coefficient of 0.89, making it closest to the positive ideal solution and showing significantly better overall benefits than other combinations. The results of this study can be used to optimize drip irrigation configurations and provide a theoretical basis for improving the yield and water use efficiency of drip-irrigated cotton.