Influence of jujube/cotton intercropping on soil temperature and crop evapotranspiration in an arid area

Intercropping is a common strategy to improve land use efficiency in many areas of the world. However, intercropping induces adaptive changes that remain poorly understood with regard to soil temperature and inter-species moisture competition. This is especially true for the interspecies relationship between intercropped jujube ( Ziziphus jujuba Mill.) and cotton ( Gossypium hirsutum L.). To gain insight into this relationship and its influence, field experiments were conducted in 2015–2017 to analyze how soil moisture and temperature were affected under jujube/cotton intercropping. Compared with single cropping, intercropping lowered the soil temperature under jujube by 0.04–0.87 ℃, and lowered soil temperature under cotton by 0.63–2.92 ℃ for all months except April and May. The soil temperature stability of intercropping was significantly higher than that of monocropping. These changes were generally conducive to crop growth, although lowered soil temperature during the later growth period was not beneficial to jujube quality. Intercropping jujube growth was inhibited not only by interspecific competition, but also by plastic film mulching of cotton. Throughout the total growth period, both transpiration and soil evaporation in intercropped jujube decreased by 12 mm and 39 mm, respectively, and crop yields decreased by 20–30%. However, due to disproportionate absorption of irrigation water by cotton, evapotranspiration during the entire growing season increased by 30 mm, and crop yield increased by 30%. In addition, through carbon stable isotope method, the transpiration ratio of single-cropped jujube and cotton was 0.79–0.85:1, and that of intercropped jujube and cotton was 0.65–0.68:1. Cotton dominated during the critical period of water demand. Therefore, although intercropping can reduce water loss by evaporation and improve the efficiency of land use, from the perspective of interspecific water relations, the dominant position of cotton had pronounced inhibitory effects on jujube. Continuous implementation of intercropping over many years is not conducive to the development of fruit tree planting, especially as trees become older.