Jonathan Kays, University of Maryland, jkays@umd.edu (Presenter)
Gary Felton, University of Maryland, gfelton@umd.edu


Nitrogen-based surface application of biosolids to hybrid poplar plantations is an operational technique in the Pacific Northwest. Many states are enacting phosphorous based nutrient management regulations but little research exists on soil P impacts of present management practices. This three-year study applied N-based biosolid rates to hybrid poplar trees over a two year period with a spring and fall applications, followed by another year of monitoring. The replicated research study treatments included a: 1) control; 2) low application rate – half the prescribed rate of 350 lbs/N/ac/yr of plant available N; 3) medium application – prescribed rate; and 4) high application rate – twice the prescribed rate. Water quality was assessed with suction lysimeters and groundwater monitoring wells, and soil samples were taken in each of the 12 plots in spring and late fall. Tree measurements were taken to quantify production and foliar leaf samples to determine nutritional status. All biosolid application resulted in P levels that exceeded Maryland nutrient management limits that would limit future applications. One year after application there was no reduction in soil P. Leaching of nitrogen or phosphorous to groundwater was not a major problem. P-based nutrient management regulations can have a significant impact on current management systems with surface biosolid application to hybrid poplar trees. Strategies and options will be discussed.