Evaluating the hydrothermal resource utilization in different canopy layers of non-mulched drip-irrigated cotton under different irrigation regimes

Non-mulched crop planting can address residual film pollution in cotton fields in arid regions. However, little is known about the efficiency of soil hydrothermal resource utilization in different canopy layers under various drip irrigation regimes in non-mulched cotton fields. Therefore, field experiments with three irrigation regimes were conducted from 2020 to 2021, including deficit (W4, 3660 m 3 ha −1 ;12‑day interval), conventional (W6, 5040 m 3 ha −1 ; 8‑day interval), and excessive (W8, 6252 m 3 ha −1 ; 6‑day interval) irrigation. The drip irrigation regimes for the treatments were the same as those in film-mulched cotton fields at the seedling and budding stages. The volume for each irrigation for each treatment during the flowering and boll-setting stages was 690 m 3 ha −1 . The effects of different drip irrigation regimes on the growth and hydrothermal resource utilization across different canopy layers of non-mulched cotton were comprehensively evaluated. The results showed that W8 resulted in the highest water consumption (WC) during the flowering and boll‑setting stages, which was 5.55%-112.43% higher than that of W4 and W6, but with lower effective accumulated temperature in soil (SEAT) during the boll‑opening stage. In 2020 and 2021, at the boll‑opening stage, the daily average effective soil temperature of W6 was 0.36 and 0.92°C higher than that of W8, respectively, and the SEAT of W6 was 4.17% and 11.11% higher than that of W8, respectively. The W8 treatment stimulated horizontal and vertical growth and yield formation in the upper canopy. The W6 treatment stimulated yield formation in the middle and lower canopies, with yield comparable to that of W8. The accumulated heat productive efficiency in soil (PE) in the lower and middle canopies of W6 was not significantly different from that of W8. However, the water use efficiency (WUE) in the lower and middle canopies was 24.37%-78.43% higher than that of W8. In summary, the irrigation regime W6 (5040 m 3 ha −1 , 8‑day interval) maintained a favorable soil hydrothermal environment, achieved total cotton yield comparable to that of W8, and improved hydrothermal resource utilization efficiency in the middle and lower canopies. This study provides an important reference for precision irrigation in non‑mulched drip‑irrigated cotton fields in arid regions.