Differential effects of rice irrigation modes on hydrothermal environment and yield from the perspective of TOPSIS model

In order to clarify the effects of different water-saving irrigation modes on hydrothermal changes in paddy fields in the black soil zone, field experiments were set up in paddy fields in the standard black soil zone in 2023 and 2024 to investigate the changing patterns of water changes, paddy field temperature changes, rice plant height, number of tillers, SPAD, and yield under the shallow-wet irrigation mode (QS), the shallow-wet-dry irrigation mode (QSG), and the deep-wet-dry irrigation mode (SSG). The results showed that (1) controlling the lower irrigation limit and increasing the upper irrigation limit improved rainfall utilisation, and the QSG mode irrigation volume was reduced by 10.27% to 44.52% compared with the QS mode irrigation volume and SSG mode irrigation volume. Increasing the upper limit of irrigation and controlling the lower limit of irrigation helped to increase the canopy temperature, water layer temperature and soil layer temperature of rice. (2) In terms of rice growth, lowering the upper irrigation limit and controlling the lower irrigation limit inhibited the growth of rice plant height. Controlling the lower limit of irrigation would increase the effective number of rice tillers and improve the stem tiller spike formation rate, but it would reduce the SPAD and dry matter accumulations. Yield in QSG mode was significantly higher than that in QS and SSG modes, by 4.12% to 4.65% and 18.42% to 14.69%, respectively. (3) Evaluating the integrated hydrothermal changes and rice growth conditions according to the TOPSIS model, the QSG model was superior to the SSG model, and finally the QS model.