Surface Covers Affect Liquid Manure Temperature, Albedo, and Evaporation

Highlights Evaporation from clear water, manure, and separated liquid manure was 4.6 mm d -1 on average. Straw, foam, geotextile, and roof covers decreased evaporation by 54%, 53%, 31%, and 21%, respectively. Albedo was highest for floating foam covers and lowest for metal roof covers. Straw, foam, and geotextile increased manure temperature compared to uncovered manure. ABSTRACT. Evaporation is a key component of the surface energy budget of liquid manure. Models rely on accurate energy budgets to predict manure temperature, which in turn is used to model temperature-dependent greenhouse gas emissions from liquid manure storages. Due to lack of data, it has been assumed that liquid manure has similar evaporative properties to water; however, this assumption may be inaccurate. Many factors, including manure crusting, covers, and turbidity, are all likely to affect the surface energy budget and the evaporation rate. This experiment investigated the differences in evaporation between eight treatments, including water, dyed water, raw and separated liquid manure, and four commonly used covers (straw, geotextile, foam, and roof), by measuring weekly evaporation. Albedo, surface temperatures, and internal temperatures were also measured to determine treatment effects. Over the 10-week study, no significant difference was found between the evaporation rates of water, raw manure, and separated liquid manure, with an average rate of 4.6 mm d -1 . Notably, the raw manure did not form a consistent surface crust, which may explain the similarities in evaporation rates in this study and is unlikely to represent manure with a crust. Overall, covers significantly decreased evaporative losses by between 21% and 54% compared to uncovered raw manure. Average evaporation rates of the covered treatments were 1.9 mm d -1 for straw cover, 2.0 mm d -1 for foam cover, 2.9 mm d -1 for geotextile cover, and 3.4 mm d -1 under a roof cover. Similarities between each treatment and water as well as between the four covered treatments and the uncovered raw manure were found using linear regression on weekly evaporation. Generally, the uncovered treatments were more similar and could be predicted (high R 2 ) by multiple linear regression with environmental variables, while the covered treatments differed more and were not as well predicted (lower R 2 ). Results from this study can help adjust evaporation rates in biophysical models to improve estimates of manure temperature, tank holdin