Abstract: The Ningxia Yellow River Irrigation Area is located in a temperate arid zone, where the development of double-cropping systems is strongly restricted by high evaporation. The application of modified carboxymethyl cellulose (CMC) can induce the binding of surface soil particles to form a soil film, achieve a mulching effect, and improve soil hydrothermal conditions. To elucidate the hydrothermal characteristics of soil film in farmland, we conducted an experiment with the treatments including ammonium carboxymethyl cellulose (CMC-NH₄) application rates of 0 (CK, control), 50 (T₁), 100 (T₂), 200 (T₃), and 300 kg·hm^-2(T₄) to induce soil film formation, and analyzed their effects on soil temperature at 20 cm depth, soil water content, and crop yield in a spring wheat-summer maize rotation system. The results showed that soil film treatments significantly reduced the daily maximum soil temperature by 5.9%-7.2% and 6.2%-15.4% during the spring wheat and summer maize growing periods, while increased the daily minimum soil temperature by 8.8%-22.1% and 6.4%-12.3%, respectively. The diurnal soil temperature variation decreased by 2.71-0.72 ℃ and 4.66-1.30 ℃, respectively. Additionally, the daily maximum soil water content decreased by 6.8%-23.4% and 1.2%-7.9%, whereas the daily minimum soil water content increased by 10.4%-33.1% and 3.9%-10.3%, leading to a reduction in diurnal soil water content difference by 10.9%-1.8% and 6.5%-1.8%, respectively. Those results indicated that the soil film effectively stabilized soil moisture dynamics. Furthermore, the yield of spring wheat and the aboveground biomass of summer maize increased by 7.3%-18.7% and 33.6%-49.0%, respectively. Soil temperature, soil water content, and crop yield increased with increasing CMC-NH₄ application rates. Soil film exhibited significant hydrothermal regulation effects, enhanced soil temperature and moisture while reduced diurnal temperature and water differences, and thereby demonstrated effective mulching functionality. These findings suggest that soil film mulching can improve crop productivity by optimizing the soil hydrothermal environment.

Key words: carboxymethyl cellulose ammonium (CMC-NH₄), soil film tillage, soil temperature, soil water content, hydrothermal effect