Waste Streams from Methane Digesters: Exporting Nutrients through Turfgrass and Forage Production Systems

Published in Agron. J. 104:1348–1355 (2012) Posted online 9 Jul, 2012 doi:10.2134/agronj2012.0005 Copyright © 2012 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. I of animal feeding operations contributes to increases in livestock numbers, nutrient loading on surrounding cropland and concerns about off-farm environmental impact (Sharpley et al., 2004). Diverting livestock waste from cropland into bioenergy facilities for methane production offers an opportunity to reduce the amount and frequency of manure applied to available cropland. However, recycling MS generated from methane digesters could pose environmental risks to surrounding cropland, similar to manure. Like manure applications, limited hauling distances necessitates cropping systems to maximize export of nutrients contained in MS. Uptake of manure and wastewater derived N and P in forage harvests has been evaluated for year-round cropping systems. Adapted forage crops were grown and harvested to remove N and P and prevent nonpoint-source losses of N and P. Woodard et al. (2007) reported annual harvests from a bermudagrass/rye cropping system removed 67 kg P ha–1 cycle–1. Ketterings et al. (2007) reported a two-cut system applied to brown midrib sorghum in New York removed up to 510 kg N ha–1 yr–1 and 101 kg P ha–1 yr–1. Brink et al. (2004) observed average uptake and export of 300 kg N ha–1 yr–1 and 46.5 kg P ha–1 yr–1 in forage harvested from Tifton 85 bermudagrass in Mississippi. However, availability and fate of nutrients in soil applied MS are uncertain and could affect biomass production, nutrient uptake, and nutrient export by forages receiving MS. Studies of manure cycling to turfgrass revealed an option for exporting two to three times more P through sod than through annual forage harvests (Vietor et al., 2002). A single harvest of Tifway bermudagrass sod exported up to 561 kg ha–1 of total N and 219 kg ha–1 of total P applied as raw or composted dairy manure (Vietor et al., 2002). Sod harvests typically removes about a 2-cm depth of soil in addition to turfgrass biomass. Calculations of nutrient export for sod includes the mass of nutrients found in soil and plant fractions of the harvested sod layer. To determine manure sources of nutrient exported by sod, nutrients found in sod grown without manure were subtracted from the amount removed by sod grown with manure (Vietor et al., 2002). The thin layer of soil removed by sod harvest is expected to effectively remove and export MS sources of organic and inorganic nutrients. While soil and turfgrass responses to nutrients and C found in compost and manures have been investigated, soil and turf responses to MS are unknown. Forage or turfgrass sod production for disposal and utilization of MS generated by bioenergy facilities would likely involve large or repeat applications of MS. Large application rates of MS necessitate production practices that optimize crop production and minimize environmental impacts. For example, amending manure with aluminum sulfate (alum) before surface application can significantly reduce concentrations of water-extractable P in soil and decrease runoff concentrations of dissolved reactive P (DeLaune et al., 2006). Mixing alum with MS before surface ABSTRACT