Effects of subsoiling depth on water use efficiency and yield of cotton field under drip irrigation in south Xinjiang, China

Abstract: Northwest China Plain has become the largest cotton production region in the world. Cotton production occupies a key position, as an important pillar industry for agricultural development in Xinjiang, China. However, continuous cropping in cotton field has caused increasingly serious shortage on the farmland water, particularly great negative effects on the soil ecological environment in the root area. Subsoiling has been an effective tillage measure to optimize the soil environment, and further to drive the process of water movement and dissipation, thereby to promote the absorption and utilization of nutrients and water in the deep soil by roots, finally to increase soil productivity and crop yields. However, the research on the response of water consumption characteristics and water use efficiency to subsoiling is lacking, particularly on the irrigated cotton area in southern Xinjiang. In this study, a positioning subsoiling experiment in a cotton cultivation field was carried out under drip irrigation with plastic film mulching from April to October of 2019 in Awati County experimental base of the arid inland Tarim Basin, Northwest China (40°06′N, 80°44′E, altitude 1 025 m). Using the non-subsoil (CK) as a control, a machete subsoiler with a depth locator was used for precise subsoiling at depths of 30 cm (TD1), 40 cm (TD2), and 50 cm (TD3). The test was performed to explore the effect of different subsoiling depths on soil bulk density, soil water consumption, evapotranspiration (ETc), water use efficiency (WUE) and the growth characteristics and crop productivity in cotton growing seasons. The results showed that the subsoiling reduced the bulk density of soil, while increased soil water consumption and evapotranspiration, thereby to improve the utilization and absorption of deep soil moisture in the rapid growth period. Compared with CK, TD1, TD2 and TD3, on average, the bulk density of 0-60 cm soil reduced by 1.0%, 1.9% and 3.3%, respectively, and the soil moisture content of 0-80 cm soil layer by 5.3%, 11.6% and 11.3% at flowering and boll stage, respectively. The subsoiling significantly increased soil water consumption and ETc in the whole growing season (P<0.05). Compared with CK, TD1, TD2 and TD3, the subsoiling significantly increased soil water consumption by 31.4, 30.0 and 47.4 mm, respectively, ETc by 6.7%, 6.3% and 10.0%. In terms of the potential of subsoiling on cotton production, the subsoiling had a significant promotion effect on cotton dry matter accumulation, yield, and water use efficiency (WUE), but it did not increase linearly with the depth of subsoiling. Especially, TD2 was more conducive to the maximum of dry matter accumulation, yield, and WUE. Compared with CK, TD1, TD2 and TD3, the dry matter accumulation increased by 11.6%, 22.5% and 20.8%, respectively, as well as the yield by 7.0%, 15.5% and 13.0%(P<0.05), respectively. TD2 increased water use efficiency (WUE) by 8.9% and 6.3%, compared with CK and TD3. The subsoiling of 40 cm can be an optimal subsoiling on the irrigated ecological cotton in the southern Xinjiang, where the rational construction of soil tillage layer, both the maximum of cotton yield and water productivity. The finding can provide a very high popularization and application for the dry farming cotton in the southern Xinjiang, China.