Kentucky bluegrass response to use of aquatic plants as a soil amendment

Rapid aquatic plant growth in Michigan's smaller lakes has reduced their navigability and recreational use. Harvested aquatic weeds have posed a new waste disposal issue for municipalities. Application of lake weeds as a soil amendment on area farms was viewed as a possible waste management option that might benefit local sod producers. The objectives of this study were to 1) estimate the amount of plant-available N (PAN) released from lake weed material, 2) determine the chemical composition of aquatic plant tissues and their effect on plant-available moisture, and 3) study turfgrass response to lake weed applications using the criteria of turfgrass quality, growth, and N uptake. Rates of lake weed refuse applied to field plots were 96,161, and 206 Mg.ha(-1). Two 47-day laboratory incubations were conducted with the same rates of refuse. Relative to biosolids, the metal content of the lake weeds was low and the nutrient content high. One megagram of lake weeds contained 0.37 kg of P and 2.5 kg of K. The decay constant for the C fraction in lake weeds was 8 to 10 days and 16 days for the N fraction. Estimates of the N supplied by lake weeds (570, 960, and 1200 kg PAN/ha) were based on data from C and N incubations. Application of lake weeds significantly increased plant-available soil moisture and significantly enhanced sod establishment and turf density, resulting in decreased weed pressure. However, excess N was present at higher application rates. Management concerns during the application of lake weeds should focus on nutrient loading and the timing of plant-available N release. Depending on methods of weed harvesting, we observed that large amounts of unwanted trash present in the plant biomass could discourage use by growers. Land application of lake weed refuse could ease waste disposal problems, reduce fertilizer inputs for sod growers, and improve the moisture status of sands. Further, this information can be of value to environmental regulatory agencies in determining safe and proper use of such waste materials.