Effects of lateral spacing for drip irrigation and mulching on the distributions of soil water and nitrate, maize yield, and water use efficiency

In this study, a two-year study in fields with and without a subsurface sand layer (identified as FSS and FNS) were conducted in the Hetao Irrigation District in Northwest China, to investigate the effects of irrigation lateral spacing and soil mulching on soil water and nitrate distribution uniformity, and the combined effects of soil water and nitrate distribution on crop yield and water use efficiency (WUE) of spring maize. The experiment followed a completely randomized block design with four treatments (S1M1, S1M2, S2M1, and S2M2) and three replicates for FSS and FNS, respectively. The four treatments resulted from the combination of two levels of lateral spacing (S1 for 1.0 m and S2 for 0.5 m) and two film-covering modes (full mulching, M1; partial mulching, M2). In each treatment, the Christiansen uniformity coefficient (CU) was used to evaluate the uniformities of soil water (CUw) and nitrate (CUn) distribution in the vertical soil profile. The results showed that the narrower lateral spacing and full mulching enhanced CUn and relative chlorophyll content of leaf, compared with the wider lateral spacing and partial mulching. However, lateral spacing and mulching methods imposed no significant effect on CUw. The correlation between CUw and CUn was not significant under mulched drip irrigation system. In soils without a subsurface sand layer, crop yield may be greater with a higher CUn in root zone. Full film-covering significantly enhanced CUn and then increased crop yields and WUE in FNS, however the combined effects of lateral spacing and mulching methods on grain yield were not significantly different. Thus, taking into account crop yields, WUE, and cost of drip laterals, the combination of wider irrigation lateral spacing and partial mulching was recommended for the FSS soil, while the combination of wider irrigation lateral spacing and full mulching for the FNS soil.