Rapid Indices of Potential Nitrogen Mineralization for Intensively Managed Hardwood Plantations

Short-rotation hardwood plantations generally require repeated applications of nitrogen (N) fertilizer to maintain desired growth and are being installed on two previous land uses: agricultural fields and cutover forest lands. Because the soil organic matter chemistry is different between agricultural field and cutover soils, indices of N availability developed for one land use or the other may not work well across both land use types. The standard aerobic incubation index is time consuming and costly. Therefore, three rapid methods were tested for estimating it on six converted agricultural fields and seven cutover pine sites currently in intensively managed sweetgum plantations on the eastern coastal plain of the United States. Two procedures (anaerobic incubation and hot KCl extract) were not useful for estimating mineralizable N in either agricultural field soils or cutover pine soils. The third index, a 3-day incubation of rewetted soils previously dried, was linearly correlated to mineralizable N (p , 0.0001, R 1⁄4 0.88). This method, which had not been tested in forest soils previously, worked best for the cutover soils (p , 0.002, R 1⁄4 0.82) and less so for the agricultural field soils (p , 0.097, R 1⁄4 0.66). However, none of Received 19 March 2004, Accepted 10 November 2004 Address correspondence to D. Andrew Scott, Southern Research Station, USDA Forest Service, 2500 Shreveport Highway, Pineville, LA 71360, USA. E-mail: [email protected] Communications in Soil Science and Plant Analysis, 36: 1421–1434, 2005 Copyright # Taylor & Francis, Inc. ISSN 0010-3624 print/1532-2416 online DOI: 10.1081/CSS-200058485