Effects of film mulching and irrigation amount on the root distribution and yield of seed-maize

Plastic film mulching and drip irrigation have been the main measures to cope with the water resources shortage for better crop productivity in the arid region of Northwest China. This study aims to explore the dynamic response of root distribution and yield of seed-maize to the plastic film mulching and irrigation amount under drip irrigation. The field experiments were conducted in the Shiyang River Basin located in the arid region of Northwest China in 2017 and 2018. Six treatments were set, including two levels of film mulching (full–mulching (M1) and non-mulching (M0)), and three levels of irrigation amount (WF, WM and WL: 100%, 70% and 40% of the irrigation water requirement, respectively). The distribution of soil water, the heat and root length density were monitored during the seed-maize growing season, whereas, the aboveground dry matter and yield were monitored in the mature period. The results showed that the average soil moisture contents of 0-60 cm soil layer were 0.22, 0.18, 0.17, 0.19, 0.20, and 0.18 cm3/cm3, respectively, under the M1WF, M1WM, M1ML, M0WF, M0WM, and M0ML treatments at 75 day after sowing (DAS). It indicated that the soil moisture content of 0-60 cm soil layer increased with the increase of irrigation amount under the same film mulching condition. Specifically, the soil moisture content of the 0-60 cm soil layer under the M1WF treatment was higher than that under the M0WF treatment in the same irrigation condition. The soil moisture contents of the 0-60 cm soil layer under the M1WM and M1WL treatments were lower than that under the M0WM and M0WL treatments, respectively. Film mulching significantly increased the soil temperature by 1.1-3.2℃ before 75 DAS, and there was no effect on the soil temperature after 75 DAS, indicating that the temperature-increasing effect of film mulching mainly appeared during the early growth stage. The root length density decreased with the deepening of soil depth under different film mulching and irrigation treatments in the various growth period of seed maize. Furthermore, 86.3%-96.7% of the roots were distributed in the 0-60 cm soil layer at 95 DAS of seed maize. The root length density was higher than 1.0 cm/cm3 in the 0-30 cm soil depth and 0-15 cm from the horizontal direction of the plant base, while lower than 1.0 cm/cm3 outside the spatial range. The root length density at 10 cm soil depth under WL treatment was 19.6%-32.5% lower than that of WF and was 0.2%-41.9% higher at deeper layer at various growth period, which showed that full irrigation was conducive to the root growth in shallow layer, while water deficit was conducive to the root growth in deeper layer. The yield and aboveground dry matter increased with the increase of irrigation amount. And the root length density at 10 cm soil depth under M1 treatment was 4.4%-69.2% higher than that of M0 treatment under different irrigation treatments, and the yield was 24.9% higher. The aboveground dry matter and yield of seed maize were closely related to the root length density at the 0-20 cm soil depth at the 75 DAS and 95 DAS, where the correlation coefficients were more than 0.883 and 0.804, respectively. Consequently, the favorable soil environment can be expected to promote the root growth for the aboveground growth of seed maize. The finding can provide a theoretical basis to implement the irrigation and film mulching measures in the Shiyang River Basin.