Spatial variability of salt content caused by nonuniform distribution of irrigation and soil properties in drip irrigation subunits with different lateral layouts under arid environments

Abstract

The nonuniformity of drip irrigation that is highly dependent on lateral layouts has been a concern for secondary soil salinization in arid regions. The effects of spatial variabilities in drip irrigated water and soil properties on soil salt content (SSC) distribution were therefore evaluated at a typical operational scale of subunits for a drip irrigation system. Two types of subunits with different lateral layouts, one with single end feeding laterals (S1) and one with dual-end feeding laterals (S2), were investigated during the 2018 and 2019 growing seasons of mulch drip irrigated cotton under arid environments. The distribution of the irrigation amount and SSC at the initial stage (prior to the first drip irrigation) and during the boll opening stage of cotton and the soil particle size distribution and bulk density in the subunits with different water feeding modes were determined. The results revealed that the Christianson uniformity coefficients (CUs) of the emitter discharge rate for S2 were 4–7% higher than those for S1, even when the area of S2 was 1.5 times that of S1. The more nonuniformly distributed irrigation water for S1 produced a more dispersed distribution of SSC, with CV ranging from 0.23 to 0.82, which was noticeably higher than the range of 0.13–0.34 for S2. The partial least squares analysis results demonstrated that the importance of the factors on the spatial variability of SSC followed an order of initial SSC > drip irrigation water > soil physical properties for S1 and initial SSC > soil physical properties > drip irrigation water for S2. The dual-end water feeding mode reduced the potential effect of the nonuniformity of irrigation water on SSC due to the improved uniformity on the subunit scale. Our study suggests that the dual-end feeding mode would be promising to avoid local salt harmfulness caused by the nonuniformity of SSC in the drip irrigation system.