Start Date: Sep 01, 2013
End Date: Aug 31, 2014
Test-tube manure water extractions will be conducted to provide data on how winter variables influence nutrient release from manure during periods of snowmelt or rain on snow. Dairy manure will be subjected to different temperature conditions, including frozen or incubated to attain temperatures of ~2°, 5°, and 10°C. These manures will be mixed in test-tubes with de-ionized water at temperatures of ~2° and 5° at water:manure dry weight equivalent solids ratios of 20, 50, 100, and 250. Mixtures will be shaken in conditions to maintain the target water temperatures for 0.5, 1, 2, and 4 hours. After shaking, samples will be analyzed for dissolved P, NH4-N, and NO3-N. Funnel and soil-column manure leaching experiments will be conducted to provide data on nutrient release from dairy manure on the soil surface during snowmelt and rain on snow. Manure and snow will be packed into 20-cm diameter plastic funnels or on top of soil columns in ways to simulate winter manure application. Manure quantities will include three equivalent field application rates of 2000, 4000, and 8000 gallons per acre, while the snow quantity will be held constant at 7.5 cm depth. Manure will be placed under snow, between two 3.75 cm snow layers, or on top of snow. Manure will be leached by water in two ways, either by snowmelt or by applying artificially simulated rain to the funnels. For the snowmelt experiments, snow in funnels will be allowed to melt under natural outdoor conditions. For rain experiments, funnels or columns will be placed under a rainfall simulator that will apply rain at a rate of ~1.5 cm per hour for 1 h, which will represent a typical winter/spring rain on snow. All water runoff samples will be analyzed for solid particle quantity and total N and P, and filtered samples (0.45 um) will be analyzed for dissolved P, NH4-N, and NO3-N. All experiments up to this point will involve ARS collaboration. Plot-scale runoff experiments will be conducted at the University of Wisconsin. Fields will represent two land uses, including a tilled, rough soil surface typical of cornfields, and a smooth soil surface typical of hay fields. These plots will be equipped with runoff collection system appropriate for this scale experiment. Dairy manure will be applied to plots to simulate typical manure application strategies, including no manure, manure applied in the fall before freezing conditions and left unincorporated over the winter, and manure applied in the winter to frozen or snow-covered soils. Runoff from naturally occurring snowmelt and rainfall events will be collected. Unfiltered runoff samples will be analyzed for sediment and total N and P, and filtered samples will be analyzed for dissolved P, NH4-N, and NO3-N. At the beginning and end of the experiments, soils will be analyzed for available N and P to determine the addition of these nutrients to soil in infiltrating manure leachate. ARS personnel will collaborate in developing a simulation model for winter manure runoff based on the existing SurPhos model, and to develop algorithms for winter conditions. Available runoff monitoring data will be used to evaluate the new winter manure P runoff model.