Exploring optimal straw mulch thickness during freeze–thaw periods in the central Yellow River basin: Field observations and numerical modelling

Straw mulch has been widely used to inhibit soil evaporation in semi-arid regions, but little attention has been given to exploring optimal straw mulch thicknesses for suppressing soil evaporation under different meteorological conditions in seasonally frozen soil regions. By combining field observations and numerical modelling, the optimal straw mulch thickness for inhibiting soil evaporation under different meteorological conditions was determined. Field experiments indicated that the cumulative soil evaporation associated with straw mulch thicknesses of 1–3 cm was 40%, 53% and 65% lower than that of bare land during freeze–thaw cycles. Compared with that of bare fields, the cumulative soil evaporation simulated by SHAW (simultaneous heat and water) decreased from 9% to 82% and from 36% to 88% during the 2017–2018 and 2018–2019 periods, respectively, when the straw mulch thickness ranged from 1 to 20 cm. The cumulative soil evaporation tended to stabilize until the straw mulch thickness reached 14.3 cm under weather conditions with low humidity, high wind speed and sunshine and 14.5 cm under weather conditions with high or moderate humidity, low or moderate wind speed and sunshine from 1987 to 2017. The results have implications for reducing nonproductive soil evaporation and improving agricultural water management in seasonally frozen regions.