Soil Tillage, Conservation & Management 1124 Agronomy Journal • Volume 103, Issue 4 • 2011 Western Oregon Grass Seed Crop Rotation and Straw Residue Effects on Soil Quality S. M. Grif fith,* G. M. Banowetz, R. P. Dick, G. W. Mueller-Warrant, and G. W. Whittaker Published in Agron. J. 103:1124–1131 (2011) Posted online 11 May 2011 doi:10.2134/agronj2010.0504 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. W estern Oregon’s Willamette Valley is the largest producer of cool-season forage and turfgrass seed in the world. Approximately 194,000 ha in the region are devoted to production of grass seed crops because the soils do not supply sufficient drainage suitable for conventional crops. Western Oregon’s marine climate and poorly drained soils offer a unique environment to study dryland crop production and soil quality due to the mild temperatures and quantities of annual precipi- tation that oſten cause semi-flooded field conditions. No such climatic and soil conditions like this exist elsewhere in the world. For decades field burning removed postharvest straw residue in grass seed production systems of the Pacific Northwest (PNW) but legislative action to enhance air quality phased out burn- ing almost completely between 1991 and 1997. is change in production practices spurred greater use of nonthermal cropping practices, such as baling and removal of postharvest straw or incor- poration into the soil, as well as crop rotations to increase crop species diversity. Seed yield of perennial ryegrass and tall fescue was greatest with direct seeding, while that of creeping red fescue was unaffected by tillage method (Nelson et al., 2006; Steiner et al., 2006). Further, seed yield from all three crops was unaffected by residue management (residue remaining vs. baled). Steiner et al. (2006), using the Revised Universal Soil Loss Equation (RUSLE), calculated that direct seeding and high straw return reduced soil erosion and determined that it cost less to implement than conventional tillage and low straw by baling and removal. Further, Nelson et al. (2006) reported that relative to conventionally tilled soil, soil microbial biomass carbon (MB C ) was 20 to 30% higher under direct seeding, regardless of soil drainage class or time of year. ey also reported that a study location in Marion County, Oregon had twice the amount of MB C compared to a site in Benton County, Oregon. Crop N uptake was lowest in the fall and highest when soil N was elevated in the spring. Tillage enhanced annual total net N mineralization at the better-drained location growing creeping red fescue for seed resulting in potentially greater leachable nitrate during the following winter high precipitation months (November–February) when the crop’s demand for N is low due to slow growth and suboptimal temperatures (Nelson et al., 2006). Tillage had little effect on net N mineralization at the poorly drained site at Linn County, Oregon. Steiner et al. (2006) reported several conservation measures that could be implemented into western Oregon grass seed produc- tion systems to benefit the grower financially, as well as improving ecosystem services and farm sustainability. Due to complex grower constraints when growing certified seed, such as meeting seed certification standards while simultaneously conserving farmland and managing pests and weeds, full adoption of conservation ABSTRACT Understanding the impact of crop rotation and residue management in grass seed production systems on soil quality and, in particular soil C dynamics, is critical in making long-term soil management decisions supporting farm sustainability. e effects of a 6-yr rota- tion and residue management (high vs. low residue) on soil quality were investigated at three locations in Oregon, each contrasting in soil drainage classification. e crop rotations were continuous perennial grass seed production, grass/legume seed production, and grass/legume/cereal seed production. e grass species grown at each location were different and represented those most commonly produced in each environment; perennial ryegrass (Lolium perenne L.), tall fescue [Schedonorus phoenix (Scop.) Holub], and creeping red fescue (Festuca rubra L.). All three grass seed crop rotations and residue methods maintained high soil quality in conventional or direct seeded soils, but under some situations, soil quality was higher with continuous grass rotation and high residue. Data suggest that straw removal for value-added use, like bioenergy production, can be accomplished in the Pacific Northwest Marine climate without appreciably affecting soil quality. Furthermore, grass seed cropping systems play an important role in soil C storage and enhancement, a valuable ecosystem service in this region where grass seed is produced on land that is not suitable for production of conventional crops that require better-drained soil. We conclude that by nature perennial grass seed crops promote high soil fertility and enriched soil C pools and consequently contribute to the tolerance of these systems to the use of less conservation-oriented crop management methods at times when crop loss could be potentially high. is attribute provides producers greater latitude in selecting soil and crop manage- ment options to address issues of soil fertility, pest, weed, or seed certification to minimize economic crop yield losses. S.M. Griffith, G.M. Banowetz, G.W. Mueller-Warrant, and G.W. Whittaker, USDA-ARS, NFSPRC, 3450 SW Campus Way, Corvallis, OR 97331; R.P. Dick, Ohio State Univ., School of Environment and Natural Resources, Columbus, OH 43210. Received 13 Dec. 2010. *Corresponding author (griffits@onid.orst.edu). Abbreviations: DOC, dissolved organic carbon; G, continuous grass seed production; GL, grass/legume seed production; GLC, grass/legume/cereal seed production; HR, high residue; LR, low residue; MB c , microbial biomass carbon; PNW, Pacific Northwest; POM, particulate organic matter; SOM, soil organic matter; SPR, soil penetration resistance; WSA, water stable aggregates. Published online July, 2011