Equivalency of Broiler Litter to Ammonium Nitrate as a Cotton Fertilizer in an Upland Soil

Agronomy Journa l • Volume 102 , I s sue 1 • 2010 251 Published in Agron. J. 102:251–257 (2010) Published online 04 Dec. 2009 doi:10.2134/agronj2009.0244 Copyright © 2010 by the American Society of Agronomy, 677 South Segoe 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. P litter, a mixture of mainly manure and bedding material, is well known as a source of mineral plant nutrients and as a soil conditioner. It has been shown to be an eff ective fertilizer for cotton (Reddy et al., 2007; Tewolde et al., 2007; Tewolde et al., 2008), corn (Endale et al., 2008; Sistani et al., 2008b), and forage and pasture crops (Evers, 1998; Sistani et al., 2008a). Th e eff ectiveness of litter as a fertilizer is associated with its ability to supply nearly all plant nutrients (Tewolde et al., 2005a; Tewolde et al., 2005b). Additionally, litter is known to improve soil physical (Brye et al., 2004), biological (Acea and Carballas, 1996; Pratt and Tewolde, 2009), and other soil properties (Gascho and Hubbard, 2006) that may contribute to improved crop performance. Th e multiple benefi ts of litter make measuring its value or its equivalency to conventional fertilizers diffi cult. Th is is particularly critical under current cotton production situations because many cotton farmers have been looking for ways to reduce the cost of production to remain profi table under the current diffi cult cotton price conditions. Many farmers in the southeastern USA, where much of the poultry litter is generated, have started to consider poultry litter as a more economical alternative to manufactured inorganic fertilizers for cotton and other row crops. Th e decision to switch to poultry litter is diffi cult because there is no easy way of determining its value relative to conventional inorganic fertilizers. Th e easiest and most common way of estimating the value of litter is based on its content of analytically determined N, P, and K. Once the N, P, and K content is known, the value of that litter is estimated based on the current price structure of commercial N, P, and K fertilizers (Kissel et al., 2008), assuming the benefi ts of the N, P, and K nutrients derived from litter are the same as those from commercial fertilizers. For example, the value of 1.0 Mg litter that contains 30 kg total N, 18 kg total P, and 25 kg total K (assuming 50–65, 90, and 100% of these nutrients, respectively, become plant available during the growing season) is estimated to be equivalent to the summed value of 15 to 20 kg N, 16 kg P, and 25 kg K derived from commercial inorganic fertilizers (Kissel et al., 2008). Th e problem with this approach is that the assumption that all litter-supplied nutrients may have the same eff ect on cotton lint yield as nutrients supplied by manufactured fertilizers may not be accurate. First, not all litter-supplied nutrients benefi t the crop. For example, cotton planted in a soil that has suffi cient K and is fertilized with litter to meet the N and P requirement does not benefi t from litter-supplied K. Additionally, littersupplied nutrients may not be in the same form as manufactured fertilizer-supplied nutrients. For example, much of the litter-supplied N is in organic form and becomes plant available gradually, whereas inorganic fertilizer-supplied N is usually 100% available for plant uptake. Also, some percentage of the analytically determined N is lost during and aft er application and does not contribute to the crop’s performance. Furthermore, litter contributes to a crop’s performance by improving soil physical and biological properties and by supplying many of the essential micronutrients. Th erefore, the value of litter may not be accurately estimated ABSTRACT