NITROGEN TRANSFORMATIONS IN PARTICLE-SIZE FRACTIONS FROM A 2ND ROTATION PINE FOREST SOIL

A second rotation forest sand (Mt Burr sand) was separated by a combination of dry sieving and winnowing into different particle sizes rich in either soil or organic matter. These fractions were analysed for % loss on ignition, % organic carbon, total organic nitrogen and mineral nitrogen. Mineralization of soil organic nitrogen and nitrification of ammonium sulphate added to these fractions were studied. Amongst the heavier fractions obtained by sieving, the <125 µm fraction (the finest) contained the highest concentration of organic and exchangeable nitrogen and was the most active in nitrogen transformations. Amongst the lighter fractions obtained by winnowing, the 125 to 500 µm fraction had the highest organic nitrogen content but mineralization of nitrogen was greatest in the 500 to 2000 µm. Nitrification of native and applied ammonium nitrogen was similar in both the 125 to 500 µm and 500 go 2000 µm organic matter fractions. © 1990, Taylor & Francis Group, LLC. All rights reserved.