TECHNICAL REPORTS 520 Brassica cover crops are new to the mid-Atlantic region, and limited information is available on their N uptake capabilities for effective N conservation. Forage radish (Raphanus sativus L. cv. Daikon), oilseed radish (Raphanus sativus L. cv. Adagio), and rape (Brassica napus L. cv. Dwarf Essex) were compared with rye (Secale cereale L. cv. Wheeler), a popular cover crop in the region, with regard to N uptake ability and potential to decrease N leaching at two sites in Maryland. Plants were harvested in fall and spring for dry matter and N analysis. Soil samples from 0 cm to 105 to 180 cm depth were obtained in fall and spring for NH 4 –N and NO 3 –N analyses. Ceramic cup tension lysimeters were installed at depths of 75 to 120 cm to monitor NO 3 –N in soil pore water. Averaged across 3 site-years, forage radish and rape shoots had greater dry matter production and captured more N in fall than rye shoots. Compared with a weedy fallow control, rape and rye caused similar decreases in soil NO 3 –N in fall and spring throughout the sampled profile. Cover crops had no effect on soil NH 4 –N. During the spring on coarse textured soil, pore water NO 3 –N concentrations in freeze-killed Brassica (radish) plots were greater than in control and overwintering Brassica (rape) and rye plots. On fine textured soil, all cover crops provided a similar decrease in pore water NO 3 –N concentration compared with control. On coarse textured soils, freeze-killed Brassica cover crops should be followed by an early-planted spring main crop. Brassica Cover Crops for Nitrogen Retention in the Mid-Atlantic Coastal Plain Jill E. Dean and Ray R. Weil* University of Maryland N utrient losses from agricultural sources were estimated to comprise 41% of the N loading to the Chesapeake Bay in 2003 (Chesapeake Bay Program, 2004). Nitrogen inputs may aggravate eutrophication of surface waters and contaminate drinking water, and the large land to water ratio within the watershed makes the Chesapeake Bay especially sensitive to nutrient pollution (Pionke et al., 2000). Cover crops provide many environmental and agronomic benefits (Weil and Kremen, 2007), including reduced soil erosion, increased soil organic matter (Fageria, 2007), alleviation of subsoil compaction (Williams and Weil, 2004), and suppression of weeds and other pests (Fisk et al., 2001). Cover crops have also been shown to be an effective means of reducing nutrient losses from agricultural lands (Jackson et al., 1993; Meisinger et al., 1991; Vos and Van Der Putten, 2004; Weinert et al., 2002). To reduce N loading to the Chesapeake Bay, the Maryland Agricultural Cover Crop Program provides financial incentives for farmers to grow small grain cover crops, such as rye (Secale cereale L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), or oats (Avena sativa L.). Te Maryland Agricultural Cover Crop Program was broadened in 2005 to include Brassica cover crop species. Rye is the most widely grown cover crop in the Atlantic Coastal Plain, and its N scavenging capacity and adaptability to the soils and climates in the region has been well documented (Coale et al., 2001; Shipley et al., 1992; Staver and Brinsfield, 1998). Rye is therefore a logical benchmark to which Brassica performance can be compared. Brassica cover crops, such as forage radish (Raphanus sativus L.), oil- seed radish (Raphanus sativus L.), and rape (Brassica napus L.), are relative newcomers to the Maryland Coastal Plain, but studies in Eu- rope, Canada, and the western regions of the USA suggest that these cover crops are effective in capturing N, in some cases outperforming rye in taking up N and decreasing soil NO 3 –N (Isse et al., 1999; Jack- son et al., 1993; Kristensen and Torup-Kristensen, 2004; Lainé et al., 1993; Torup-Kristensen, 1994; Torup-Kristensen, 2001; Vos and Van Der Putten, 2004; Weinert et al., 2002). Kristensen and Torup-Kristensen (2004) observed total plant N uptake of forage radish to be significantly greater than rye, with values of 158 and 90.5 kg N ha −1 , respectively. Biomass production and N uptake by rye declines with delay in date of planting in the fall (Feyereisen et al., Abbreviations: CMREC, University of Maryland Central Maryland Research & Education Center-Beltsville facility; WREC, University of Maryland Wye Research & Education Center; CMREC1, University of Maryland Central Maryland Research & Education Center-Beltsville facility study year 1 site; WREC1, University of Maryland Wye Research & Education Center study year 1 site; CMREC2, University of Maryland Central Maryland Research & Education Center-Beltsville facility study year 2 site; WREC2, University of Maryland Wye Research & Education Center study year 2 site. 1109 HJ Patterson Hall, Dep. of Environmental Science and Technology, Univ. of Maryland, College Park, MD 20742. Copyright © 2009 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including pho- tocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Published in J. Environ. Qual. 38:520–528 (2009). doi:10.2134/jeq2008.0066 Received 5 Feb. 2008. *Corresponding author (rweil@umd.edu). © ASA, CSSA, SSSA 677 S. Segoe Rd., Madison, WI 53711 USA TECHNICAL REPORTS: PLANT AND ENVIRONMENT INTERACTIONS