Agronomy Journal  Volume 103, Issue 3  2011 899 Soil Fertility & Crop Nutrition Incorporation of Municipal Biosolids Affects Organic Nitrogen Mineralization and Elephantgrass Biomass Production Miguel S. Castillo, Lynn E. Sollenberger,* João M. B. Vendramini, Kenneth R. Woodard, George A. O’Connor, Maria L. Silveira, and Jerry B. Sartain Published in Agron. J. 103:899–905 (2011) Published online 28 Mar 2011 doi:10.2134/agronj2010.0497 Copyright © 2011 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. 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. A dequate nutrient supply is necessary to meet the requirements of high-yielding bioenergy crops. Land applica- tion of MBS has been shown to be an efective alternative for reducing the amount of inorganic fertilizer used in bioenergy crop production systems (Heller et al., 2003; Castillo et al., 2010b). Use of MBS also recycles nonrenewable resources and addresses the problem of inding alternative options for MBS disposal. Like many other organic sources of nutrients, when MBS is applied on an N-rate basis there is potential for overapplication of P due to the narrower N:P ratio in MBS vs. plant require- ments. Typical concentrations of total N and P in MBS range from 35 to 68 and 18 to 39 g kg –1 , respectively (USEPA, 1999). hus, in some cases application of MBS is limited to P-based rates. Another issue of signi icance when using MBS is that ~800 g kg –1 of the total N is in organic forms (Sommers, 1977; Binder et al., 2002), meaning that this N is not immediately available for plant uptake. Plant-available nitrogen (PAN) in MBS is a function of the initial inorganic N concentration (NH 4 –N and NO 3 –N) and the proportion of organic N that mineralizes over time (Gilmour and Skinner, 1999). Organic N mineralization occurs through the activity of nonspeciic heterotrophic soil microorganisms (Jarvis et al., 1996; Pierzynski et al., 2000; He et al., 2003). he rate and quantity of mineralization largely depends on the quantity and composition of the organic matter (Sommers et al., 1981) and the inluence of the environment on biological activity (Goncalves and Carlyle, 1994; Castillo et al., 2010a). hus, placement of the organic substrate (soil-incorporated vs. surface-applied), results in diferences in microenvironmental conditions (e.g., contact of MBS with moist soil particles and microbes) and may inluence the dominant forms of N (NH 4 –N vs. NO 3 –N) and rates of organic-N mineralization (Terry et al., 1978; Clark and Gilm- our, 1983; Gilmour and Clark, 1988; He et al., 2003). Experiments with poultry litter and cattle manure have demonstrated beneits of soil incorporation. hese include reduction in N volatilization losses, odors, and residue cover as well as an increase in organic N mineralization and crop yields (Hanna et al., 2000; Pote et al., 2003; Sharpe et al., 2004). Several laboratory incubation studies have demonstrated the positive efects of incorporation of organic materials produced in wastewater treatment plants (King, 1973; Terry et al., 1978; Sommers et al., 1981; Adamsen and Sabey, 1987; He et al., 2003). Fewer data have been reported from actual ield-incuba- tion trials (He et al., 2000; Hanselman et al., 2004) and from studies that have measured plant responses (e.g., DM yield) as an indicator of organic N mineralization. Although soil incorporation as a nutrient management practice has been studied and recommended for a variety of organic and inorganic sources, little attention has been given to the efect of incorporation of MBS on plant DM yield. hus, two experiments were conducted under ield conditions to assess the efects of incorporation of Class A MBS on plant and soil responses and on decomposition and organic N mineraliza- tion rates of MBS. he objectives of Exp. 1 were to: (i) quantify ABSTRACT Municipal biosolids (MBS) represents an alternative source of nutrients for the production of bioenergy crops like elephantgrass (Pennisetum purpureum Schum.). Two experiments were conducted during 2 yr in Florida to evaluate the efect of soil incorporation vs. surface application of MBS on: (i) elephantgrass dry matter (DM) yield, tissue N and P concentration and removal, and soil C and P (Exp. 1); and (ii) organic N mineralization and DM decomposition rates of MBS measured in the ield using a litter bag incubation technique (Exp. 2). In Exp. 1, three treatments supplied 350 kg total N ha –1 yr –1 from surface-applied municipal biosolids (MBS- SA), soil-incorporated municipal biosolids (MBS-INC), and surface-applied ammonium nitrate (NH 4 NO 3 ). A fourth treatment provided 700 kg total N ha –1 yr –1 from MBS-SA (double rate of municipal biosolids, 2x-MBS). In Exp. 2, MBS was ield incubated in litter bags placed on the soil surface or at a 5-cm soil depth. Elephantgrass DM yield, and N and P removal were greater for MBS- INC than MBS-SA. Dry matter yield for MBS-INC was not diferent than for NH 4 NO 3 fertilizer (22.5 vs. 24.3 Mg ha –1 ). Removal of N and P increased 39 and 10 kg ha –1 yr –1 , respectively, for MBS-INC and MBS-SA. Total organic N mineralized was greater for MBS-INC (386 g kg –1 ) than MBS-SA (308 g kg –1 ). Incorporation of MBS increases elephantgrass DM yield and nutrient removal compared to surface application and allows MBS to replace a greater proportion of inorganic N fertilizer. M.S. Castillo, L.E. Sollenberger, and K.R. Woodard, Agronomy Dep., Univ. of Florida, Gainesville, FL 32611-0500; J.M.B. Vendramini and M.L. Silveira, Range Cattle Research and Education Center, Ona, FL 33865; G.A. O’Connor and J.B. Sartain, Soil and Water Science Dep., Univ. of Florida, Gainesville, FL 32611. Received 7 Dec. 2010. *Corresponding author (lesollen@ul.edu). Abbreviations: BDR, biosolids decomposition rate; DM, dry matter; MBS, municipal biosolids; MBS-INC, municipal biosolids, soil incorporated; MBS-SA, municipal biosolids, surface applied; 2x-MBS, double rate of municipal biosolids; NMR, nitrogen mineralization rate; WEP, water-extractable phosphorus.