Nitrate Leaching From Intensive Forest Management on Abandonded Agricultural Land: Fifth-Year Results

Abstract

This report is on the fifth year results of a cooperative research project to examine water quality impacts of maximizing plantation growth on abandoned agricultural land, first reported after two years in the Ninth Southern Silvicultural Research Conference. The study, located on International Paper's Southland Experimental Forest at Bainbridge GA, examines growth of loblolly pine (Pinus taeda L.) and sweet gum (Liquidambar styraciflua L.) with complete vegetation control, irrigation, fertilization, and pest control as a factorial experiment on an abandoned agricultural field. Groundwater quality was measured in the maximum (all combined) and minimum (only vegetation control), the old field without plantation management, natural forest, and along the shore of Silver Lake. After two years groundwater nitrate concentrations in all the plots in the abandoned field violated drinking water standards (> 10mgN/l) and were significantly higher than the natural forest or lake edge. Soil moisture nitrate was significantly higher in the plots with vegetation control. After five years the number of violations and maximum nitrate concentrations have declined by roughly 50%. Soil moisture nitrate concentrations have declined significantly in the plantation plots in the last three years, at shallow depths. Concentrations at the five foot depth below the minimum treatment plots approached that found in the natural pine < 0.5mgno₃-N/l. 3 Growth rates have been large in all treatments except the sweet gum minimum treatment. Irrigated loblolly plots have accumulated over 250 kgN/ha from the soil pool in the abandoned field. The nitrogen pools within the soil have been sufficient to continue nitrate leaching for five years and supply 200-300 kg N/ha to the control and irrigated (only) pines.

Citation

Williams, Thomas M.; Gresham, Charles. 2002. Nitrate Leaching From Intensive Forest Management on Abandonded Agricultural Land: Fifth-Year Results. In: Gen. Tech. Rep. SRS-48. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. pg. 20-25