insect and weed densities (Goosey et al., 2004, 2005;. Hatfield et al., 2007a, b). Additionally, weaned lamb production is feasible on weedy barley (Thomas et al.
Proceedings, Western Section, American Society of Animal Science Vol. 58, 2007 SHEEP GRAZING WHEAT SUMMER FALLOW AND THE IMPACT ON SOIL NITROGEN, MOISTURE, AND CROP YIELD E. E. Snyder1, H. B. Goosey1, P. G. Hatfield1, and A. W. Lenssen2 1
Montana State University, Bozeman, MT, 59717 2
USDA, ARS, Sidney, MT, 59270
ABSTRACT. In typical dryland farming areas of Montana, annual precipitation is not sufficient for annual harvest of small grains. Summer fallow in alternate years, is a common method of conserving soil moisture to produce a crop in the following season. Current methods of fallow management are primarily mechanical tillage and spraying with herbicides. Although these methods are effective, they are expensive, making fallow management the highest variable cost associated with dryland grain production. The objectives of this study were to compare the impact of grazing small grains stubble with sheep, as a fallow management tactic, against traditional management practices of chemical and mechanical fallow across two cropping systems on wheat grain yield and soil nitrate-nitrogen and moisture. Fallow management treatments (chemical, mechanical, graze) were imposed, in a randomized complete block split-plot design, on spring wheat-fallow and winter wheat-fallow cropping systems in a 6 ha 45 plot study at Montana State University’s Fort Ellis Research Center near Bozeman, MT. Data on treatment impact on wheat yield and soil nitrate-nitrogen and gravimetric water concentration were recorded. Wheat yields did not differ between cropping system (P > 0.50). Soil nitrate-nitrogen (P > 0.43) and percent gravimetric water (P > 0.06) within either spring wheat-fallow or winter wheat-fallow cropping systems did not differ among fallow treatments at 0-15 cm, 15-30 cm, and 30-60 cm soil depths. This study demonstrates that grazing sheep on winter or spring wheat stubble and associated summer fallow does not negatively impact soil nitrate-nitrogen, percent gravimetric water, or subsequent crop yield.
variable cost associated with dryland grain production (Johnson et al., 1997). One of the greatest challenges for fallow management is the prevention of weed growth without increasing soil erosion (Fenster, 1997). research
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Sheep can graze both dormant perennials crops (i.e., alfalfa) and small grains fallow to manage both pest insect and weed densities (Goosey et al., 2004, 2005; Hatfield et al., 2007a, b). Additionally, weaned lamb production is feasible on weedy barley (Thomas et al. 1990) and wheat stubble (Brand et al. 1999). Mullholland et al. (1976) suggested that cereal stubble that contained some green plant material offered an acceptable grazing resource for wethers and dry ewes at stocking rates of 4.25 sheep/ha for 11 weeks (330 sheep d/ha). Targeting sheep and small grains production in a mutually beneficial partnership has the potential to reduce production costs for both enterprises. The objective of this study was to determine the impact of grazing small grains stubble with sheep, as a fallow management tactic, against traditional management practices of chemical-fallow and mechanical-fallow in two farming systems: 1) spring wheat-fallow and 2) winter wheat-fallow), on wheat grain yield and soil NO3 and moisture. Materials and Methods Research was conducted from 2004 to 2006 at Montana State University’s Fort Ellis Experiment Station, near Bozeman, Montana (Universal Transverse Mercator (UTM) 12 501833E, 5056909N; North American Datum (NAD) 1927) (Fig. 1). Fallow treatments were imposed on 0.14 ha plots in a randomized complete block split-plot design with cropping system as a main-plot factor and fallow management as a sub-plot factor. Each phase of each rotation was represented every year (Fig. 2). Subplot fallow treatments were: 1) Graze Fallow (i.e., grazing sheep), 2) Chemical Fallow (i.e., herbicides), and 3) Mechanical Fallow (i.e., tillage). Treatments were imposed on two main-plot cropping systems: 1) Spring wheat-fallow, 2) Winter wheat-fallow. Spring wheat
Key Words. Small ruminant, Grain yield, Sustainable agriculture, Cereal stubble, Soil Introduction In dryland grain farming areas of Montana annual precipitation frequently is insufficient for profitable annual cereal cropping. Instead, a cropsummer fallow system is used to increase soil moisture and available nitrate-nitrogen (NO3) for subsequent crop growth. Current methods of fallow management are primarily mechanical tillage and spraying with herbicides (i.e., chemical fallow). These methods are effective but expensive, making fallow management the highest
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plots were seeded to ‘McNeal’. Winter wheat plots were seeded to ‘Promontory’. Data presented here are a small part of a much larger study.
dimethylamine salt of dicamba. Wilbur-Ellis R-11® surfactant was used at a rate of 0.3 l/ha. Herbicide application was done at 8 km/hr and 40 psi using an engine powered (Briggs & Stratton Corporation, Milwaukee, WI) Broyhill® Stadium 302.8 liter sprayer with a 3.05 m spray boom mounted on a utility vehicle. Mechanical Fallow. Mechanical fallow was completed using a John Deere 740 tractor pulling a John Deere 100 toolbar equipped with cultivators tilling soil to an approximate depth of 15 cm. Graze Fallow. Graze fallow was done using a variety of class and age of western white faced sheep that, within a fallow period, were randomly assigned to fenced plots at the beginning of each grazing session. Stocking rates ranged from 29 to 153 sheep days/ha (Goosey et al., 2005; Hatfield et al., 2007 a, b, c). Water and white salt were available ad-libitum. Each grazing session ended when approximately 6.5 kg/plot or less green weeds and volunteer cereal plants remained.
Fig. 1. 2004 Aerial photograph of study site. Mech Fallow even S wheat odd 101 Fallow
Fallow even S wheat odd
Chem 201 Fallow Chem 202 Fallow Chem 203 Fallow Chem 204 Fallow 205 Chem Fallow
Mech Fallow even 102 Fallow W wheat odd
Fallow even W wheat odd
Mech W wheat even 103 Fallow Fallow odd
W wheat even Fallow odd
Mech S wheat even 104 Fallow Fallow odd
S wheat even Fallow odd
S wheat even 105 Mech S wheat odd Fallow
S wheat even S wheat odd
Graze S wheat even Fallow odd 106 Fallow
S wheat even Fallow odd
W wheat even 107 Graze Fallow Fallow odd
W wheat even Fallow odd
Graze S wheat even 108 Fallow S wheat odd
S wheat even S wheat odd
Graze Fallow even 109 Fallow S wheat odd
Fallow even S wheat odd
Fallow even 110 Graze W wheat odd Fallow
Fallow even W wheat odd
Chem S wheat even Fallow odd 111 Fallow
Graze S wheat even 211 Fallow odd Fallow
Mech S wheat even 311 Fallow odd Fallow
Fallow even 112 Chem Fallow S wheat odd
Fallow even 212 Graze Fallow S wheat odd
Fallow even 312 Mech Fallow S wheat odd
Chem W wheat even 113 Fallow Fallow odd
Graze W wheat even 213 Fallow Fallow odd
Mech W wheat even 313 Fallow Fallow odd
Chem S wheat even 114 S wheat odd Fallow
Graze S wheat even 214 S wheat odd Fallow
Mech S wheat even 314 S wheat odd Fallow
Fallow even 115Chem Fallow W wheat odd
Fallow even 215 Graze Fallow W wheat odd
Fallow even 315 Mech Fallow W wheat odd
Mech Fallow Mech 207 Fallow Mech 208 Fallow Mech 209 Fallow Mech 210 Fallow 206
Sample Collection. Cropping System Yield. Yield was determined by harvesting ripe grain (i.e., 0.16) for any variable tested therefore data were combined and analyses were recalculated using only the effect of treatment across year. Grain yields within either spring or winter wheat cropping system did not differ (P > 0.50) among fallow treatments (Table 1). No differences were detected
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among treatment for NO3 (P > 0.43) or percent gravimetric water (P > 0.06) within either spring wheatfallow or winter wheat-fallow cropping systems at 0-15 cm, 15-30 cm, or 30-60 cm soil depths (Table 1). Gravimetric water concentrations vary between treatments in the spring wheat-fallow cropping system (15-30 cm) by 1.1% and 2.2 % in the winter wheat-fallow system (0-15 cm). Although not different these tendencies, particularly during drought years, could become apparent.
systems. Currently a need exists for long-term ‘enterprise-level’ research addressing the economics of sheep grazing fallow. Literature Cited
Anderson, R.L. 1999. Cultural strategies reduce weed densities in summer annual crops. Weed Technology 13: 314-319. Brand, T.S., F. Franck, A. Durand, J. Coetzee. 1999. The intake and nutritional status of sheep grazing wheat stubble. Small Rum Res. 35: 29-38. Fenster, C.R. 1997. Conservation tillage in the northern Great Plains. J. Soil Water Conserv. 32: 37-42. Goosey, H.B., P.G. Hatfield, S.L. Blodgett, S.D. Cash. 2004. Evaluation of alfalfa weevil (Coleoptera: Curculionidae) densities and spring regrowth characteristics of alfalfa grazed by sheep in winter and spring. J Entomol. Sci. 39: 598-610. Goosey, H.B., P.G. Hatfield, S.L. Blodgett, R.W. Kott, and T.M. Spezzano. 2005. The potential role of sheep in dryland grain production systems. J. Agric. Envir. Eco. 111: 349-353. Hatfield, P.G., S.L. Blodgett, T.M. Spezzano, H.B. Goosey, A.W. Lenssen, and R.W. Kott. 2007a. Incorporating sheep into dryland grain production systems: I. Impact on over-wintering larva populations of wheat stem sawfly Cephus cinctus Norton (Hymenoptera: Cephidae). Small Rum. Res. 67: 209-215 Hatfield, P.G., A.W. Lenssen, T.M. Spezzano, S.L. Blodgett, H.B. Goosey, and R.W. Kott. 2007b. Incorporating sheep into dryland grain production systems: II. Impacts on changes in biomass and weed density. Small. Rum. Res. 67: 216-221. Hatfield, P.G., H.B. Goosey, T.M. Spezzano, S.L. Blodgett, A.W. Lenssen, and R.W. Kott. 2007c. Incorporating sheep into dryland grain production systems: III. Impact on changes in soil bulk density and nutrient profiles. Small Rum. Res. 67: 222-231. Greb, B.W. 1981. Significant research findings and observations from the Central Great Plains Research Station and Colorado State University Experiment Station Cooperating: Historical Summary 1900-1981. Akron, CO. Johnson, J.B., W.E. Zidack, S.M. Capalbo, J.M. Antle, D.F. Webb. 1997. Pests, Pesticide Use, and Pesticide Costs on Larger Central and Eastern Montana Farms with Annually-Planted Dryland Crops. Department of Agricultural Economics and Economics. Montana State University Departmental Special Report #23. Mulholland, J.G., J.B. Coombe, M.Freer, W.R. McManus. 1976. An evaluation of cereal stubbles for sheep production. Aust. J. Agric Res. 27, 881-893. Thomas, V.M., A.L. Frey, R.F. Padula, C.M. Hoaglund, C. K. Clark. 1990. Influence of supplementation on weight gain of lambs grazing barley stubble. J. Prod. Agric. 3. 106-109.
Discussion No published studies exist examining the relationship between cereal fallow managed by sheep grazing and subsequent crop yields. Our data indicates that, over two years (one full crop-fallow rotation), yield was not compromised by sheep grazing when compared to chemical and mechanical fallow management. Hatfield et al. (2007c) reported, in an eight site study, no detrimental effects on soil nutrient profiles (K, EC, NO3, OM, P, pH) from sheep grazing cereal fallow compared to tillage and burning. Our results concur with Hatfield et al. (2007c) regarding NO3. Additionally, Hatfield et al. (2007c) indicates no consistent changes in soil bulk density from grazed, tilled and burned cereal fallow plots. Goosey et al. (2005) also reported no differences in soil bulk density or gravimetric water concentration between grazed and non-grazed plots. Results from the current study concur with those of Goosey et al. (2005). Hatfield et al. (2007b) documented that sheep grazing was as effective as mechanical tillage for managing weeds in winter wheat stubble. However, this study did not include summer fallow Weed growth in cereal fallow can reduce subsequent wheat yields by 509 to 1525 kg/ha (Greg, 1981), largely through their use of soil moisture. Therefore, sheep grazing, with the intent of killing actively growing weeds, should have positive effects on soil moisture, assuming bulk density and water infiltration are not adversely impacted. Over the first two years of our study, sheep grazing winter and spring wheat-fallow has demonstrated equal conservation of soil NO3 and gravimetric moisture, the two primary components associated with crop yield in the semiarid northern Great Plains, compared to traditional fallow management practices. However, differences among grazing and cropping systems, as a whole, may require additional years for treatment differences to become apparent. This research needs to be conducted over a longer time period to investigate any long-term changes. Implications
Compared to other forms of fallow management sheep grazing fallow has the potential to be a viable alternative. Although soil NO3 and gravimetric water concentrations were not adversely impacted, a need exists for additional research addressing the economic considerations associated with these types of grazing
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Table 1. Grain yield1, soil nitrogen1 and soil moisture1 in 2005 and 2006 of winter and spring wheat plots summer fallowed by mechanical, chemical, and sheep grazing
Mechanical5 (M)
Yield (kg/ha)2 NO3 Nitrogen 0-15 cm (ppm)3 NO3 Nitrogen 15-30 cm (ppm)3 NO3 Nitrogen 30-60 cm (ppm)3 % Gravimetric4 Water 0-15 cm3 % Gravimetric4 Water 15-30 cm3 % Gravimetric4 Water 30-60 cm3
Yield (kg/ha)2
3423
Chemical6 (C)
3446
Grazed7 (G)
S.E.
Spring Wheat-Fallow 3246 201
M vs. G P-value
C vs. G P-value
0.54
0.50
18.5
17.9
20.2
3.12
0.71
0.63
4.1
5.0
5.1
1.02
0.49
0.93
4.9
6.2
4.0
1.86
0.74
0.43
20.3
20.3
21.5
0.68
0.20
0.20
12.7
12.6
13.7
0.37
0.11
0.07
12.3
12.1
11.4
0.37
0.11
0.21
0.67
0.87
3082
2808
Winter Wheat-Fallow 2890 323
NO3 Nitrogen 19.2 23.1 18.4 5.25 0.91 0.53 0-15 cm (ppm)3 NO3 Nitrogen 15-30 cm (ppm)3 5.2 4.4 3.9 0.97 0.35 0.70 NO3 Nitrogen 30-60 cm (ppm)3 2.7 3.1 3.1 0.88 0.75 0.96 % Gravimetric4 Water 23.3 22.2 21.1 0.71 0.06 0.31 0-15 cm3 % Gravimetric4 Water 13.1 12.6 12.1 0.49 0.13 0.40 15-30 cm3 % Gravimetric4 Water 11.8 11.4 11.5 0.43 0.61 0.94 30-60 cm3 1 No year x treatment interactions were detected P> 0.16. 2 7 September 2005; 28 August 2006. 3 27 September 2005; 29 September 2006. 4 Gravimetric Water = (Wet Weight – Dry Weight / Dry Weight) X 100. 5 Shallow tillage (10cm) conducted with John Deer 740 tractor pulling a John Deer 100 toolbar 6 Chemical fallow conducted with Gly Star Plus® at the rate of 1.17 liters/ha mixed with 1.75 liters/ha of dimethylamine salt of dicamba. 7 Graze fallow: completed using a variety of class and age of western white faced sheep. Stocking rates ranged from 29 to 153 sheep days/ha
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