Waste Streams from Methane Digesters: Exporting Nutrients through Turfgrass and Forage Production Systems

Similar to manure, residual manure solids (MS) from methane digesters require cropping systems and management practices that optimize nutrient export to prevent large increases in soil P levels. The objectives were to compare forage and turfgrass sod production systems with respect to effects of MS management practices on soil properties and crop productivity and to compare mass balance of N and P on field scale. A 2-yr field experiment was conducted on a fine sandy loam soil receiving MS to compare nutrient imports, forms in soil, and export by Tifton 85 bermudagrass (Cynodon spp.) grown for forage and Tifway bermudagrass [C. dactylon (L.) Pers. × C. transvaalensis (Burtt-Davy)] grown for turfgrass sod. Five soil treatments for each crop included MS with and without Alum topdressed (250 kg total phosphorus [TP] ha−1) annually or a single application of MS (500 kg TP ha−1) incorporated compared to soil without MS. One harvest of Tifway sod removed 2.7 times more total nitrogen (TN) and 2.8 times more TP than three harvests of Tifton 85 forage biomass during the first year of production. Greater biomass production and nutrient uptake by Tifton 85 forage during the second production season reduced the difference in nutrient export between Tifton 85 and Tifway sod. Turfgrass sod production systems can be used by producers to increase export of MS applied nutrients compared to forage production and enable waste streams from methane digesters to be recycled.