Submitted to: ASA-CSSA-SSSA Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: November 6, 2005
Publication Date: November 6, 2005
Citation: Tolk, J.A., Evett, S.R., Howell, T.A. 2005. Nighttime evapotranspiration from alfalfa and cotton in a semiarid environment [abstract]. Agronomy Abstracts, ASA-CSSA-SSSA Annual Meeting, Salt Lake City, Utah. 2005 CDROM. Technical Abstract: Nighttime evapotranspiration (ETN) has typically been neglected in estimating water loss from land surfaces. Our objective was to quantity the contribution of ETN to daily (24-h) ET24 of irrigated and dryland cotton (Gossypium hirsutum L.) and irrigated alfalfa (Medicago sativa L.) grown in semiarid climate. The results were then examined using a numerical simulation model ENWATBAL which provided separate calculations of soil water evaporation and crop transpiration. Nighttime ET was measured at Bushland, TX, using weighing lysimeters containing monolithic soil cores of Pullman clay loam (fine, mixed, superactive thermic Torrertic Paleustoll) for alfalfa in 1998 and cotton in 2001. The ETN of alfalfa averaged 6.9% of ET24, with losses exceeding 1 mm occurring on at least 10 nights, with a maximum loss of 1.94 mm. Average ETN of cotton contributed from 3% under dryland conditions to 7% under fully irrigated conditions. The largest single ETN event was 1.35 mm, with events exceeding 1 mm occurring six times. Model simulations indicated that the ETN of alfalfa consisted of about 60% soil water evaporation and 40% transpiration, and that of irrigated cotton was 80% soil water evaporation and 20% transpiration. The model energy balance outputs shows that measured ETN was most responsive to sensible heat exchange between the air and canopy, which was a function of the humidity deficit between the leaf and air and canopy resistance to latent heat flux. Nighttime ET can be an important part of total ET or irrigated crops in a semi-arid environment.