Nitrate leaching from intensive fiber production on abandoned agricultural land

Abstract

Loblolly pine ( Pinus taeda L.) and sweetgum ( Liquidambar styraciflua L.) were grown with irrigation, continuous fertilization, and insect pest control on a one-year-old abandoned peanut ( Arachis hypogaea L.) field. Wells and tension lysimeters were used to measure nitrate in soil moisture and groundwater on three replicate transects for two years. Each replication had five treatments: maximum plantation management, minimum plantation management, old field, natural forest, and lake edge. Maximum plantation management included select genetic stock, irrigation, fertilization, complete elimination of competing vegetation, and insect pest control. Minimum plantation management included select genetic stock and complete elimination of competing vegetation. The old field was the abandoned peanut field with no treatment. The natural forest was a 50-year-old longleaf pine ( Pinus palustris Mill.) forest. The lake edge was a narrow wetland transition form the longleaf forest to the lake. Groundwater nitrate concentration beneath the minimum treatment (8.10 mg NO 3-N/l) was significantly higher than the maximum treatment and the old field (5.84 and 5.05 mg NO 3-N/l, respectively). All three treatments frequently exceeded the 10 mg NO 3-N/l drinking-water standard. The forest and lake edge were both significantly lower at 0.30 and 0.32 mg NO 3-N/l, respectively. Averaged over all depths, soil-moisture nitrate concentrations in the two plantation treatments were significantly higher (11.4 and 11.5 mg NO 3-N/l) than the old field (5.40 mg NO 3-N/l) which was significantly higher than the forest edge (0.24 mg NO 3-N/l). Nitrate leaching contaminated groundwater throughout the abandoned field, and all plantation treatments exacerbated the problem.