A Water-Energy Balance Approach to Quantify Manure Management Under Frozen Conditions.

Wintertime manure application is a necessary practice for many dairy producers, but the potential for nutrient transport is high during winter and spring melt events. Prior to the 1980s, the timing of these applications was tested relative to snow cover as a strategy to reduce nutrient losses during thaw. The results were inconclusive, however, because variability in weather and the complexity of frozen soils confounded the observational study designs used. Consequently, wintertime manure regulations are loosely supported by data and nutrient management tools have a limited capacity to account for frozen conditions. Therefore the objectives of this study include to: 1) quantify water balances to elucidate the mechanisms that control infiltration and runoff on frozen agricultural soils and 2) quantify energy balances to link changes in melt rates and water movement to management practices. A replicated field study will be conducted for three winter seasons under conventional and no tillage in south central Wisconsin. Three liquid manure application timing treatments will be tested: unmanured controls, early applications to frozen ground (prior to snowfall), and mid-winter applications to snow-covered ground. Measurements will include radiation, albedo, temperature, wind speed, heat flux, soil moisture, matric potential, runoff, and precipitation. Field data will be supplemented with simulations with the Simultaneous Heat and Water (SHAW) model. Increasing our knowledge of winter processes and generating replicated field data will help inform management tools that evaluate nutrient losses from agroecosystems to balance environmental and economic viability.