Determination of feedyard evaporation using weighing lysimeters

Six shallow, weighing lysimeters were installed near Etter, TX, to measure quasi-instantaneous evaporation rates from simulated feedyard surfaces. The data revealed a pronounced and consistent hygroscopic period during which the manure appears to have absorbed water from the atmosphere. Daily measurements during late autumn 2003 showed lysimeter evaporation to be 30% of reference evapotranspiration (ET o) of well-watered grass. Warm-season data from an upgraded load-cell system capable of continuous monitoring showed lysimeter evaporation to be poorly correlated with ET o, with a mean of approximately 20% and a range of 15-30%. The lower ratio in the most recent data may be attributed to (a) smaller manure particle size and greater sorptive affinity as compared to the first experiment, (b) increased evaporative demand in the warm-season experiment, which may not have been satisfied due to a flux-limiting hydraulic conductivity in the manure matrix and (c) other unknown factors that require further investigation. The hygroscopic behavior of the manure surface during the nighttime hours dramatically decreases the net daily evaporation, is loosely associated with a decrease in the vapor pressure deficit and reduces the expected water needs for feedyard dust control. Future investigations will quantify the sensitivity of the evaporation rate to surface roughness, manure particle size, target moisture content and advanced manure/soil layering procedures.

Determination of feedyard evaporation using weighing lysimeters Conference Paper