Impacts of lateral spacing on the spatial variations in water use and grain yield of spring wheat plants within different rows in the drip irrigation system

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Xinjiang Uyghur Autonomous Region of China has seen the successful application of drip irrigation to wheat production to cope with the extreme shortage of fresh water resources. However, the cost is high with one drip tube serving only four rows of wheat plants in the current irrigation pattern. Here, performances of irrigation patterns differing in ratios of drip tube to plant rows (TR) were compared in a field experiment in the growth seasons of spring wheat in 2014 and 2015. Three ratios were set: one tube served four (TR4, as control), five (TR5) and six (TR6) rows of plants (row spacing: 15 cm), respectively. Variations in grain yield and water use efficiency (WUE) were observed between different wheat rows (R1, R2 and R3 indicated the 1st, 2nd and 3rd rows close to the drip tube, respectively). Grain yield declined in all the rows as the TR ratio increased, with more obvious yield decrease in R3 and R2 than in R1. The ratios of the yield decrease to the decrease in received irrigation water (RIW) in R3 and R2 were not proportionally lower relative to R1; the range of yield decrease was much smaller than the range of RIW decrease in R3 and R2. This was because the decreases in the leaf area index and in the relative water content in the flag leaf of plants were less than that in RIW in R3 and R2 relative to R1, and because of the compensation effect of the enhanced contribution of the redistributed dry matter stored in the vegetative organs before anthesis being translocated into the grains after anthesis in the plants of R3 and R2. This mechanism would be helpful for developing new and economical drip irrigation patterns for wheat production with a higher TR ratio.