SSSAJ: Volume 73: Number 5 • September–October 2009 1575 1 Formerly at USDA-ARS,New England Plant, Soil and Water Res. Lab., Orono, ME 04469 Soil Sci. Soc. Am. J. 73:1575-1586 doi:10.2136/sssaj2008.0303 Received 23 Sept. 2008. *Corresponding author (harry.schomberg@ars.usda.gov). © 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. A vailability of N from soil organic matter during a growing sea- son is a function of many biotic and abiotic factors, including cropping history, management, climate (temperature and water availability), and the interacting efects of soil C cycling (Grifn, 2008). Estimating the N mineralization potential of a soil is of con- siderable importance for maximizing N-use efciency from all N sources and minimizing environmental losses. Eforts to develop quick biological or chemical methods for identifying the miner- alization potential of organic N have a long history (reviewed by Bremner, 1965; Keeney, 1982; Bundy and Meisinger, 1994; Grifn, 2008) with various levels of success. Several of these methods closely correspond to the mineralizable N component (Grifn, 2008). Harry H. Schomberg* USDA-ARS J. Phil Campbell, Sr. Natural Resource Conservation Center Watkinsville, GA 30677 Sirio Wietholter Empresa Brasileira de Pesquisa Agropecuária (Embrapa Trigo) Passo Fundo Rio Grande do Sul, Brazil 99001-970 Timothy S. Griffin 1 Friedman School of Nutrition Sci. and Policy Tufts Univ. Boston, MA 02111 D. Wayne Reeves USDA-ARS J. Phil Campbell, Sr. Natural Resource Conservation Center Watkinsville, GA 30677 Miguel L. Cabrera Univ. of Georgia Dep. of Crop and Soil Sciences Athens, GA 30602 Dwight S. Fisher Dinku M. Endale USDA-ARS J. Phil Campbell, Sr. Natural Resource Conservation Center Watkinsville, GA 30677 Jeff M. Novak USDA-ARS Coastal Plains Soil, Water, and Plant Res.Ctr. Florence, SC 29501 Kip S. Balkcom Randy L. Raper USDA-ARS National Soil Dynamics Lab. Auburn, AL 36832 Newell R. Kitchen USDA-ARS Cropping Systems and Water Quality Res. Unit Columbia, MO 65211 Martin A. Locke USDA-ARS National Sedimentation Lab. Oxford, MS 38655 Kenneth N. Potter USDA-ARS Grassland Soil and Water Res. Lab. Temple, TX 76502 Robert C. Schwartz USDA-ARS Southern Plains Conserv.Production Rese. Lab. Bushland, TX 79012 Clinton C. Truman USDA-ARS Southeast Watershed Res. Lab. Tifton, GA 31793 Don D. Tyler Univ. of Tennessee Biosystems Engineering and Soil Science Dep. Jackson, TN 38301 NUTRIENT MANAGEMENT & SOIL & PLANT ANALYSIS Assessing Indices for Predicting Potential Nitrogen Mineralization in Soils under Different Management Systems A reliable laboratory index of N availability would be useful for making N recommendations, but no single approach has received broad acceptance across a wide range of soils. We compared several indices over a range of soil conditions to test the possibility of combining indices for predicting potentially mineralizable N (N 0 ). Soils (0–5 and 5–15 cm) from nine tillage studies across the southern USA were used in the evaluations. Long-term incubation data were ft to a frst-order exponential equation to determine N 0 , k (mineralization rate), and N 0 * (N 0 estimated with a fxed k equal to 0.054 wk −1 ). Out of 13 indices, fve [total C (TC), total N (TN), N mineralized by hot KCl (Hot_N), anaerobic N (Ana_N), and N mineralized in 24 d (Nmin_24)] were strongly correlated to N 0 (r > 0.85) and had linear regressions with r 2 > 0.60. None of the indices were good predictors of k. Correlations between indices and N 0 * improved compared with N 0 , ranging from r = 0.90 to 0.95. Total N and fush of CO 2 determined afer 3 d (Fl_CO2) produced the best multiple regression for predicting N 0 (R 2 = 0.85) while the best combination for predicting N 0 * (R 2 = 0.94) included TN, Fl_CO2 , Cold_N, and NaOH_N. Combining indices appears promising for predicting potentially mineralizable N, and because TN and Fl_CO2 are rapid and simple, this approach could be easily adopted by soil testing laboratories. Abbreviations: Ana_N, anaerobic N mineralization; TC, total carbon; Ca_hypcl, calcium hypochlorite; Cold_N, KCl extractable NO 3 –N; CT, conventional tillage; Fl_CO2, fush of CO 2 during 3 d; Hot_N, hot KCl extractable NH 4 –N; Hyd_N, hydrolyzable N; k, mineralization rate constant; TN, total nitrogen; NaOH_N, sodium hydroxide distillable N; N 0 , potentially mineralizable N; N 0 *, value of N 0 determined using a fxed value for k; Nmin_24, N mineralization during 24 d; NP, not plowed (prairie soil); NT, no-Tillage; NT+SS, no-tillage with non- inversion subsurface deep tillage; PB_N, phosphate-borate distillable N; POMC, particulate organic matter C; POMN, particulate organic matter N; SM, stubble mulch tillage (sweeps to undercut weeds); ST, strip tillage (in-row subsoil for disruption of subsurface pan and coulters for preparation of narrow strip of tilled soil).