Evaporation from Ridge‐Tilled Soil Covered with Herbicide‐Killed Winter Wheat

Abstract

AbstractCotton (Gossypium hirsutum L.) in the High Plains of Texas is frequently planted in ridge‐tilled soil covered with standing winter wheat (Triticum aestivum L.) residue created by killing the wheat in the spring with a herbicide. A study was conducted on an Olton sandy clay loam (fine, mixed, thermic Aridic Paleustoll) to determine how the winter wheat residue affects the surface energy halance and water vapor conductance of ridge‐furrow tilled soil. Surface energy‐balance measurements were obtained with the Bowen ratio method and evaporation from the residue was estimated gravimetrically. Flux measurements were combined with measurements of vapor density at the surface and at an elevation of 1 m to calculate a conductance for water vapor transport. Although the residue was tall (0.25 m) and relatively dense (76% ground cover), evaporation from the soil beneath the residue after irrigation was high, accounting for >60% of net irradiance (Rn). Evaporation from the residue itself was negligible. The combination of standing residue and ridge‐tilled soil created high spatial variability in the energy balance, and in surface vapor density and wind speed, suggesting high spatial variability in evaporation and soil drying. The residue decreased evaporation from wet soil, and wind enhanced vapor transport through the residue. Conductances calculated for bare, ridged soil were 1.2 to 2.7 times higher than values obtained in the presence of residue, with differences between bare and residue‐covered soil increasing with wind speed. Water vapor conductance increased linearly with wind speed measured at 1.0 m, but values were lower than those reported in the literature for other residue systems.