Effects of aeration on the growth and water use efficiency of cotton under mulched drip irrigation in the dry areas of Northwest China

Abstract: Low-oxygen stress can pose a considerable threat to cotton production in the Xinjiang dry regions of Northwest China. Aerated irrigation has been widely considered to optimize the soil water-aeration environment, thus mitigating the adverse effects of low oxygen stress on the crop. However, aerated irrigation can also increase the irrigation time for less irrigation efficiency. Therefore, it is very necessary to consider the sensitivity of the cotton to hypoxic stress at different growth stages. A reasonable mode of aerated irrigation can also be established to quantify the response of the cotton growth and yield to the hypoxic stress during cultivation. Moreover, there is no consensus on the sensitivity of the cotton to low oxygen stress at various growth stages at present. This study aims to determine the effects of aerated irrigation at different growth stages on the soil environment, cotton growth, yield, and water production. A correlation was also made between the soil oxygen concentration, soil respiration rate, and soil temperature, with the cotton growth and yield. A field experiment was then conducted at the Key Laboratory of Modern Water-saving Irrigation of Xinjiang Production and Construction Corps at Shihezi University in Xinjiang, China, in 2021. The experimental settings were aerated irrigation (the dissolved oxygen concentration of 15 mg/L), and conventional non-aerated treatment (CK, the dissolved oxygen concentration of 5 mg/L) at the seedling (AS), budding (AB), flowering and boll (AF), budding, flowering and boll (ABF), and seedling, budding, flowering and boll (AW) stage. There were a total of 18 plots with three times repeated. The cotton variety was selected as "Xin Lu early 42", which was sown on April 15 and harvested on September 30. The subsurface drip irrigation was adopted for aerating using Mazzei air injector. A measurement was conducted on the soil oxygen content, soil respiration rate, soil temperature, plant height, stem diameter, leaf area index, yield, yield components, and water use efficiency. The results showed : 1 ) Soil oxygen content increased significantly under aerated irrigation. The peak values of soil respiration and soil temperature in seedling and budding aeration treatments appeared at the end of budding stage (day 92), while the peak value of aeration in flowering and boll stage was delayed compared with other treatments, which prolonged the aeration effect and improved the soil environment. 2) At seedling stage, aerated irrigation had no significant effect on plant height, stem diameter and leaf area index of cotton. At the squaring stage, aerated irrigation only had a significant positive effect on plant height; at the full budding stage, aerated irrigation had significant effects on plant height, stem diameter and leaf area index of cotton. At the initial flowering stage, aerated irrigation had significant effects on stem diameter and leaf area index. 3) The aerated yield at seedling stage was higher, the water use efficiency was lower, and the aerated yield at budding stage was the lowest compared with other aerated treatments. Aeration at flowering and boll stage not only obtained the maximum yield, but also had the highest water use efficiency. There was no significant difference in yield between aeration at seedling, bud, flowering and boll-setting stage and that at flowering and boll stage, but the water use efficiency was lower than that of aeration at flowering and boll stage. The results showed that aerated irrigation at flowering and boll stage could alleviate the cotton low-oxygen stress caused by film mulching and improve yield and water use efficiency. Consequently, the aerating in the early stage of cotton growth was beneficial to the strong seedlings, while the middle stage was easy to cause the cotton branches and leaves to grow, and the most suitable period for aerating to improve yield was the late stage. As such, aerated irrigation was recommended at the flowering and boll stage in terms of energy loss, nutrient distribution, and cotton yield. The finding can provide a theoretical basis to reveal the effect of aerated irrigation on cotton growth, thus improving the utilization of soil and water resources.