Simulating Alternative Dryland Rotational Cropping Systems in the Central Great Plains with RZWQM2

Published in Agron. J. 102:1521–1534 (2010) Published online 17 Aug. 2010 doi:10.2134/agronj2010.0141 Copyright © 2010 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. T winter wheat production in a wheat–fallow rotation with conventional mechanical tillage in the Great Plains faces a number of natural resource conservation and quality issues that can aff ect the productivity and livelihood of the region’s farmers. Because water is generally the most yield-limiting factor in the semiarid climate of the Great Plains, a 14-mo fallow period between crops has traditionally been used to increase stored soil water before planting, thereby increasing the subsequent crop yield (Greb, 1979). Notwithstanding the potential yield-stabilizing merits of fallow, this practice has oft en been the cause of severe soil erosion and quality degradation in the region (Bowman et al., 1999). Th e loss of soil quality resulting from conventionally tilled fallow has raised concerns about the long-term sustainability of wheat– fallow. Sustainable farming systems must make use of diversifi ed crops and rotations to mitigate the negative impacts of the wheat–fallow monoculture in the Great Plains (Anderson et al., 1999; Bowman et al., 1999; Shanahan et al., 1988; Norwood et al., 1990: Dhuyvetter et al., 1996). Long-term experiments that focus on reducing the amount of summer fallow time and reversing the soil degradation using no-till were established in eastern Colorado in 1985 (Peterson and Westfall, 2004). In those experiments, cropping system intensifi cation (reduced fallow frequency) increased annualized grain and residue yields by 75 to 100%, and net return to farmers by 25 to 45%. In addition, soil organic carbon was found to be impacted signifi cantly to a depth of 5 cm with an increase of 35% in the 12 yr of study compared to the WF system (Sherrod et al., 2003). Another cropping system experiment with decreased tillage and various degrees of increased cropping intensity involving a variety of summer crops (such as corn, proso millet, foxtail millet (Setaria italica L. Beauv.), sorghum [Sorghum bicolor (L.) Moench], fi eld pea (Pisum sativum L.), sunfl ower (Helianthus annuus L.), canola (Brassica napus L.), triticale (X Triticosecale rimpaui Wittm, etc.) was established in 1991 at the Central Great Plains Research Station, USDA-ARS, Akron, CO in the Great Plains of the United States (Anderson et al., 1999). Many potential alternative crop rotations for the semiarid Great Plains have been investigated since the 1990s with promising results that encourage farmers to adopt environmentally friendly farming practices (Acosta-Martınez et al., 2007; Vigil and Nielsen, 1998; Nielsen et al., 1996). However, uncertainty exists with regard to the specifi c impacts of these alternative cropping systems on sustainable crop production, natural resource conservation, and long-term soil and water quality issues. Also, in view of the large-scale spatial heterogeneity associated with the landscapes in the semiarid regions, questions arise on the validity of extrapolating the location-specifi c ABSTRACT