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ARS Home » Plains Area » Bushland, Texas » Conservation and Production Research Laboratory » Soil and Water Management Research » Research » Publications at this Location » Publication #159879
Title: NIGHTTIME EVAPORATION FROM COTTON AND ALFALFA IN A SEMIARID CLIMATE

Author
item Tolk, Judy
item Howell, Terry
item Evett, Steven - Steve

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2006
Publication Date: 5/3/2006
Citation: Tolk, J.A., Howell, T.A., Evett, S.R. 2006. Nighttime evaporation from cotton and alfalfa in a semiarid climate. Agronomy Journal. 98:730-736.

Interpretive Summary: Evaporation from agricultural lands at night has not been considered to be an important part of the daily water balance. We measured evaporation and environmental conditions during the night for irrigated alfalfa, irrigated cotton, and dryland cotton to determine how much water was evaporated and what factors might be affecting it. The environmental factors evaluated were vapor pressure deficit (VPD), wind, net radiation, soil temperature, and the temperature difference between the air and the plant canopy (TaTc). Average nighttime evaporative losses of cotton ranged from 3% under dry soil conditions to 8% of the total daily water loss under wet soil conditions, with rates of 0.1 to 0.7 mm night**-1. Average nighttime evaporative losses from alfalfa were about 8% of the total daily water loss under both wet and dry soil surface conditions, with rates of 0.6 mm night**-1. Nighttime evaporation of alfalfa under extreme advective conditions exceeded 1.5 mm night**-1. Sensible heat transfer (indicated by the magnitude of TaTc), VPD, and wind significantly affected evaporation under wet soil surface (irrigated) conditions. Net radiation was the most significant variable for the lower evaporation amounts from drier, more exposed soil surfaces of the dryland cotton crop. Nighttime evaporation may be a significant component of total water use in a semiarid climate, especially under irrigated conditions.

Technical Abstract: Nighttime evaporation has typically been neglected in estimating evaporation from land surfaces. Our objectives were to quantify the contribution of nighttime evaporation to daily evaporation of irrigated alfalfa (Medicago sativa L.) and irrigated and dryland cotton (Gossypium hirsutum L.) grown in a semiarid climate. Using multiple linear regression analysis, we also evaluated how much variability in nighttime evaporation could be explained by differences in vapor pressure deficit (VPD), wind, net radiation (Rn), soil temperature (Ts), and the temperature difference between the air and the plant canopy (TaTc). Nighttime evaporation was measured at Bushland, TX using weighing lysimeters containing monolithic soil cores of Pullman clay loam (fine, mixed, superactive thermic Torrertic Paleustoll). Average nighttime evaporative losses of cotton ranged from 3% under dry soil conditions to 8% of the total daily evapotranspiration (ET) under wet soil conditions, with rates of 0.1 to 0.7 mm night**-1. Average nighttime evaporative losses from alfalfa were about 8% of the total daily ET under both wet and dry soil surface conditions, with rates of 0.6 mm night**-1. Nighttime evaporation of alfalfa under extreme advective conditions exceeded 1.5 mm night**-1. Sensible heat transfer (indicated by the magnitude of TaTc), VPD, and wind significantly affected evaporation under wet soil surface (irrigated) conditions. Net radiation was the most significant variable for the lower evaporation amounts from drier, more exposed soil surfaces of the dryland cotton crop. Nighttime evaporation may be a significant component of total water use in a semiarid climate, especially under irrigated conditions.