Mineral Sources of Calcium and Phosphorus in Soils of the Northeastern United States

SSSAJ: Volume 72: Number 6 • November–December 2008 Soil Sci. Soc. Am. J. 72:1786-1794 doi:10.2136/sssaj2007.0344 Received 19 Sept. 2007. Corresponding author ([email protected]). © Soil Science Society of America 677 S. Segoe Rd. Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Understanding mineral sources of Ca in soils of the northeastern United States is important because plant-available Ca has been leached from the soil at accelerated rates for several decades (Lawrence et al., 1999; Likens et al., 1998), possibly resulting in Ca limitation in some forest ecosystems (Horsley et al., 2000; Huntington, 2005; Long et al., 1997). Plagioclase, the dominant Ca-bearing mineral in noncarbonate soils in the region, weathers too slowly to compensate for the Ca lost from the exchangeable pool (Likens et al., 1998; Nezat et al., 2004). Apatite, Ca5(PO4)3(F,Cl,OH), although it is usually present only in trace amounts, may be an important mineral source of Ca because it dissolves several orders of magnitude more rapidly than plagioclase (Oxburgh et al., 1994; Valsami-Jones et al., 1998; Welch and Ullman, 1993). For example, at the Hubbard Brook Experimental Forest in New Hampshire, apatite represents <1% of the soil mineral mass (12% of total Ca) yet its dissolution is responsible for at least 20% of the Ca weathered from the soils since the area was deglaciated 14,000 yr ago (Nezat et al., 2004). In the Adirondack Mountains, apatite accounts for ?1 to 8% of the total Ca in some soil parent materials (Yanai et al., 2005). Apatite is common in igneous, metamorphic, and sedimentary rocks. In igneous rocks, apatite is found in both plutonic and volcanic rocks ranging in chemical composition from Carmen A. Nezat* Dep. of Geological Sciences Univ. of Michigan 1100 North University Ave. Ann Arbor, MI 48109