LOSS OF NITROGEN AND BASES AFTER FERTILIZATION OF 2ND-GROWTH HARDWOODFOREST SOILS

Soils at five New York sites of a nitrogen fertilization study in seco nd-growth mixed deciduous forests were sampled to determine the fate o f applied N and possible adverse chemical changes from its application . Organic layer and mineral soil (0-10 cm) samples were collected 10 o r 11 years after the initial application from plots receiving a total of 0, 672 and 1344 kg-N ha-1 in two equal-sized applications 5 years a part. Nitrogen was applied as ammonium nitrate, except the first appli cation at one location was urea. Treatments had little effect on the N and C pools of the forest floor and surface soil, indicating no appre ciable retention of added N in the upper soil. Concentration and mass of cations in the mineral soil decreased with added N, as did pH, in a ccord with an hypothesis of nitrate leaching. The estimated loss of ba se cations was modest ( 1 2.4 kmol ( + ) ha-1) relative to the anions added in the highest single application of N (24 kmol ( - ) ha-1). On such soils, N added in excess of plant uptake capacity is not immobili zed by long-term storage in soil organic matter despite its wide C:N r atio. The reduction in pH entails a loss of effective cation exchange capacity in addition to the associated loss of base cations.