Effects of different machine-harvested cotton planting patterns and planting densities on soil hydrothermal conditions and cotton yield

A perfect matching between current machine-harvested cotton pattern and agricultural machinery can greatly contribute to fiber quality and the picking rate in mechanical harvesting. An effective way can be to optimize the row space, thereby to achieve the integration of agricultural machinery and agronomy for machine-harvested cotton. In this study, two machine-harvested cotton patterns were selected, including the “aimizao” planting pattern (six lines per film with wide-narrow row spacing, 66+10 cm), and the “kuanzaoyou” planting pattern (three lines per film with equal row spacing, 76 cm) in 2018-2019, as well as 3 planting densities of 135 000, 180 000 and 225 000 plants/hm2. The dynamic changes of soil temperature and soil moisture were monitored during the whole cotton growth period, and the water use efficiency was analyzed combined with the cotton yield, in order to compressively evaluate the applicability of different machine-harvested cotton pattern. The results showed that different machine-harvested cotton patterns and planting densities can affect the soil temperature, but there was no interaction effect. The variation characteristics of soil temperature were consistent under different treatments. With the increase of atmospheric temperature, soil temperature increased, but decreased rapidly and fluctuated after the cotton ridges were closed. There was no significant difference in soil temperature of plough layer under different planting patterns and planting densities in the early growth stage (May to June). However, the soil temperature in flowering and boll setting stage increased by the “kuanzaoyou” planting pattern, where 1.7 ℃ on average higher than that of “aimizao” planting pattern. The accumulated soil temperature of plough layer in the whole growth period under the “kuanzaoyou” pattern significantly increased by 8.3%-9.9% (P<0.05), compared with that of the “aimizao” pattern. In the water consumption during the whole growth period, the water consumption in the “kuanzaoyou” pattern was lower than that of the “aimizao” pattern, but the difference was not significant. Increasing planting density can reduce the accumulated temperature of plough layer, but increase the water consumption of the cotton field. Compared with the “aimizao” planting pattern in 2019, the “kuanzaoyou” planting pattern significantly increased the yield and water use efficiency by 17.5% and 18.8% (P<0.05), respectively. It infers that the “kuanzaoyou” pattern can be used to improve the soil hydrothermal conditions of cotton growth, and thereby to achieve a significant increase in yield and water use efficiency. A more suitable mechanically picked planting pattern can be widely used to promote the cotton mechanical harvesting in Xinjiang, China.