Yield of non-film cotton and the response of temperature, humidity and salt in the root zone to irrigation

Abstract: Plastic-film pollution is the limiting factor for the efficient and sustainable development of cotton in Xinjiang in western China. This study aims to explore the mechanism of non-film cotton, moisture, temperature and salt concentration in the root zone under the deep and night irrigation for the future cotton production. An experiment was carried out at the Scientific Observation and Experimental Station of Crop Water Efficient Water Use (Shihezi) (45°38′N, 86°09′E) of the Ministry of Agriculture from 2019 to 2020. The total amount of precipitation during the cotton growth period in 2019 was higher than that in 2020. The daily average maximum and minimum temperatures were both lower than that in 2020. Under the condition of equal row spacing and high density planting (26 plants/m2), the early-maturing land cotton variety 'Xinluzao 74' was used as a test material (the growth period was 120 d). 5 irrigation water treatments (W1, 2 649 m3/hm2; W2, 2 925 m3/hm2; W3, 3 201 m3/hm2; W4, 3 477 m3/hm2; W5, 3753 m3/hm2) were set up (Among them, W1-3 treatment was the average drip volume of underground drip irrigation, and W4-5 treatment was the average drip volume of field film mulching water-saving drip irrigation). Some parameters were evaluated, including the formation of cotton yield, and the change of moisture, temperature and salt concentration in the root zones. The results showed that the seed cotton yield in 2020 increased by 45.6%-65.5%, compared with 2019 (P<0.05). W4 treatment was higher with 4.1%-10.3% increment, compared with other treatments (P<0.05). The total number of bolls per unit area and the weight of a single boll increased by 4.2%-11.4% and 2.2%-4.1% in W4 treatment, compared with other treatments (P<0.05). Soil water content was ranked in order of W5 (W4, W3, W2) before the full flowering period > W1. There was no significant difference between the treatments after the full flowering period, but 21.2%-35.0% lower than that before the full flowering period (P<0.05). The soil temperature of W4 treatment was 0.4%-1.3% and 0.4%-2.4% higher than other treatments at 0-55 and 95-135 d after sowing, respectively (P>0.05). The soil pH was lower in the W4 treatment; The soil electrical conductivity was 6.4% to 19.4% higher than other treatments in the 0-30 cm soil layer under W3 treatment (P<0.05). The correlation analysis showed that the seed cotton yield was significantly positively correlated with the soil conductivity at 10 cm, but significantly negatively correlated with pH (P<0.05); it was significantly positively correlated with 20 cm soil conductivity and soil water content during flowering. It was significantly negatively correlated with temperature and pH in the late period of the boll (P<0.05). Accordingly, an irrigation volume of 3 477 m3/hm2 can be expected to create a suitable temperature and salt environment in the root zone (especially >10-20 cm soil layer) for cotton growth under the condition of no-film high-density deep layer and night drip irrigation. As such, the yield can be up to 4 873 kg/hm2, indicating the high goal of efficient production in filmless cotton.