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. C rop diversification, reduced fallow periods, and limited inputs are being promoted in the Great Plains to improve economic and environmental sustainability in dryland cropping systems (Peterson et al., 1993). In Montana, more than 1.59 million ha or 36% of the dryland acreage for annual crop production was in summer fallow in 2003 (NASS, 2010). Producers are encouraged to diversify crops away from monocultures, primarily wheat (T. aestivum L.), to reduce the area of land under fallow, and to reduce farm inputs, especially those that have negative impacts on economic and environmental sustainability (Matson et al., 1997; Struick and Bonciarelli, 1997; Gregory et al., 2002). Water typically is the primary limiting factor for growing crops in durum-based cropping systems in the semiarid northern Great Plains (NGP). Conventional summer fallow usually increases both soil water storage and NO 3-N concentration for subsequent crop use. Summer fallow, however, is ineffi cient for precipitation storage, averaging only 25% effi ciency in tilled systems (Farahani et al., 1998). Intensifi cation of crop production by reducing summer fallow provides more effi cient utilization of water in the semiarid central Great Plains (Farahani et al., 1998). Available N is the second most limiting factor for dryland crop production in semiarid agroecosystems (O'Leary and Connor, 1997). Soil NO 3-N availability is usually related to cereal yields. Increased NO 3-N content can also contaminate surface and groundwater due to N leaching and surface runoff. For decreasing fertilizer N applications and improving N utilization, producers are encouraged to diversify away from cereal monocultures, primarily spring wheat and durum, to improve crop N uptake and reduce residual soil N and N leaching. Additionally, purchasing fertilizer N is a signifi cant expense for producers. Improved nutrient-use effi ciency, particularly N, is an important goal in cropping systems (Karlen et al., 1994; Raun and Johnson, 1999). Huggins and Pan (2003) showed determination of key indicators of nitrogen use effi ciency (NUE) in cereal-based agroecosystems enabled broad assessment of agronomic management and environmental factors related to N use. Key indicators of NUE include N in grain and N aboveground biomass, N harvest index, and grain N accumulation effi ciency. Annual cereal forage crops are well adapted to semiarid NGP

Cover crops are suites of non-marketable plants grown to improve soil tilth and reduce erosion. Despite these agronomic benefits, the use of cover crops is often limited because they do not provide a direct source of revenue for producers. Integrating livestock to graze cover crops could provide both an expeditious method for cover crop termination and an alternative source of revenue. However, there has been little research on the agronomic impacts of grazing for cover crop termination, especially in horticultural market-gardens. We conducted a 3-year study comparing the effects of sheep grazing to terminate a four species cover crop (buckwheat, sweetclover, peas and beets) with those of mowing on soil quality indicators, cover crop termination efficacy, and subsequent cash-crop yields. In addition, we tested the nutritional quality of the cover crop as forage. Compared with mowing, sheep grazing did not affect soil chemistry, temperature or moisture. Our study demonstrates that sheep grazing removed more cover crop biomass than mowing at termination. The assessment of nutritional indices suggests that the four-species cover crop mixture could provide high-quality forage with a potential value of US$144.00-481.80 ha −1 of direct revenue as a grazing lease. Cash-crop yields did not differ between previously grazed and previously mowed plots in the subsequent growing season. We conclude that integrating sheep grazing into market vegetable garden operations could make cover crops more economically viable without having adverse effects on subsequent cash crops.

Sheep {Ovis aria L.) grazing, an effective method of controlling weeds and pests in a wheat [Triticum aestivum L.)-fallow system, may affect dryland soil properties and wheat yield. We evaluated the effects of Fallow management for weed concrol and soil water conservation (sheep grazing, herbicide application [chemical], and tillage [mechanical]) and cropping sequence (continuous spring wheat [CSW], spring wheat-fallow [SW-F], and winter wheat-fallow [WW-F]) on soil nutrients and chemical properties in the 0-to 60-cm depth and wheat yield. The experiment was conducted in a Blackmore silt loam from 2004 to 2008 in southwestern Montana. Soil P and K concentrations at 0 to 30 cm were lower in the grazing than in the chemical or mechanical treatments. In contrast, soil Na, Ca, and Mg concentrations were greater in the grazing and mechanical than the chemical treatment. SoilMg concentration at 30 to 60 cm was greater under CSW than WW-R Soil SO^-S concentration varied with fallow management and cropping sequence. Soil pH, cation exchange capacity (CEC), and electrical conductivity (EC) at 0 to 15 cm were greater in the mechanical than in the chemical or grazing treatments. Annualized wheat yield was greater under CSW than SW-F or WW-F but was not affected by fallow management. Sheep grazing affected soil nutrients probably by consumingwheat residues but returning them at various levels through feces and urine. In contrast, tillage increased pH, CEC, and EC, probably by incorporating crop residue, feces, and urine into the soil. By applying enough P and K fertilizers to wheat and using less intensive grazing, sheep grazing can be used to sustain wheat yields without seriously affecting soil nutrients and chemical properties.

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Sheep (Ovis aries) grazing during fallow for weed control in wheat (Triticum aestivum L.)-fallow systems may infl uence soil C and N levels and grain yields by returning part of consumed crop residue to the soil through feces and urine. We evaluated the eff ects of fallow management (sheep grazing [grazing], herbicide application [chemical], and tillage [mechanical]) for weed control and soil water conservation and cropping sequence (continuous spring wheat [CSW], spring wheat-fallow [SW-F], and winter wheat-fallow [WW-F]) on soil organic carbon (SOC), inorganic carbon (SIC), total nitrogen (STN), NH 4 -N, and NO 3 -N levels at the 0-to 120-cm depth and wheat yield. Th e experiment was conducted in a Blackmore silt loam (fi ne-silty, mixed, superactive, frigid Typic Argiustolls) from 2004 to 2008 in southwestern Montana. Annualized wheat grain and biomass yields were greater in CSW than in SW-F and WW-F and greater in 2004 than in other years. From 2004 to 2007, SOC concentration at 0-to 15-cm declined by 2.99 g C kg -1 yr -1 .In 2008, SOC content at 10 to 120 cm was greater in the mechanical or chemical than in the grazing treatment in CSW and SW-F. Th e STN content at 0 to 5 cm was greater in the chemical and mechanical than in the grazing treatment but at 30 to 60 cm was greater in the grazing than in the chemical treatment in CSW. From 2004 to 2006, NO 3 -N content at 0 to 60 cm was greater in SW-F or WW-F than in CSW. In 2008, NO 3 -N content at 30 to 120 cm was greater in CSW and SW-F than in WW-F and at 60 to 90 cm was greater in the mechanical than in the chemical treatment. Th e SIC and NH 4 -N contents were largely not infl uenced by treatments. Continuous tillage, followed by reduced amount of wheat residue returned to the soil from 2004 to 2007 probably reduced soil C and N storage. In contrast, greater amount of N removed by wheat grain due to continuous cropping probably reduced soil NO 3 -N in CSW. For sustaining wheat yields and maintaining soil C and N levels, reduced tillage with continuous cropping and less intensive sheep grazing that increase the amount of wheat residue returned to the soil could be adopted.