Integrating sheep grazing into wheat–fallow systems: Crop yield and soil properties

The two predominant systems for weed management in summer fallow are tillage with a field cultivator or multiple applications of broad spectrum herbicides with zero tillage. Both systems are based on substantial use of off farm resources. Our objective was to determine if strategic grazing of sheep may allow grain growers to more sustainably manage crop residues, volunteer crop, and other weeds during fallow periods. We conducted a study near Bozeman, Montana, USA, comparing three fallow weed management systems in two crop rotations from 2005 to 2008. Fallow weed management systems were conventional tillage, chemical-fallow (herbicide application), and sheep grazing. The crop rotations were summer fallow–spring wheat and summer fallow–winter wheat. In late fall, chemical-fallow treatment had greater residue cover and soil water content than did tilled- or grazed-fallow. At 0–15-cm depth, soil had lower bulk density in chemical- and tilled-fallow than in grazed fallow. Similarly, soil NO3-N, Ca, SO4-S concentrations and EC were lower following grazed-fallow than tilled-fallow, but Na concentration was higher following grazed-fallow than tilled- or chemical-fallow. Following spring and winter wheat, soil properties were not influenced by treatments. Grain yield was greater in winter wheat than in spring wheat but the trend reversed in protein concentration. Although soil properties varied among treatments, fallow management system had little influence on yield or quality of spring and winter wheat. Sheep grazing during fallow periods had limited impact on subsequent wheat yield and quality, and is a suitable practice for weed and residue management in wheat–fallow systems

Beyond Infinity: Georg Cantor and Leopold Kronecker's Dispute over Transfinite Numbers

Thesis advisor: Patrick ByrneIn the late 19th century, Georg Cantor opened up the mathematical field of set theory with his development of transfinite numbers. In his radical departure from previous notions of infinity espoused by both mathematicians and philosophers, Cantor created new notions of transcendence in order to clearly described infinities of different sizes. Leading the opposition against Cantor's theory was Leopold Kronecker, Cantor's former mentor and the leading contemporary German mathematician. In their lifelong dispute over the transfinite numbers emerge philosophical disagreements over mathematical existence, consistency, and freedom. This thesis presents a short summary of Cantor's controversial theories, describes Cantor and Kronecker's philosophical ideas, and attempts to state clearly their differences of opinion. In the end, the author hopes to present the shock caused by Cantor's work and an appreciation of the two very different philosophies of mathematics represented by Cantor and Kronecker.Thesis (BA) — Boston College, 2005.Submitted to: Boston College. College of Arts and Sciences.Discipline: Philosophy.Discipline: College Honors Program

Particulate and active soil nitrogen fractions are reduced by sheep grazing in dryland cropping systems

Sheep (Ovis aries L.) grazing, a cost-effective method of weed control compared to herbicide application and tillage, may influence N cycling by consuming crop residue and weeds and returning N through feces and urine to the soil. The objective of this experiment was to evaluate the effect of sheep grazing compared to tillage and herbicide application for weed control on soil particulate and active soil N fractions in dryland cropping systems. Our hypothesis was that sheep grazing used for weed control would increase particulate and active soil N fractions compared to tillage and herbicide application. Soil samples collected at the 0–30 cm depth from a Blackmore silt loam were analyzed for particulate organic N (PON), microbial biomass N (MBN), and potential N mineralization (PNM) under dryland cropping systems from 2009 to 2011 in southwestern Montana, USA. Treatments were three weed management practices [sheep grazing (grazing), herbicide application (chemical), and tillage (mechanical)] as the main plot and two cropping sequences [continuous spring wheat (Triticum aestivum L.; CSW) and spring wheat–pea (Pisum sativum L.)/barley (Hordeum vulgare L.) mixture hay–fallow; W–P/B–F] as the split-plot factor arranged in randomized complete block with three replications. The PON and MBN at 0–30 cm were greater in the chemical or mechanical than the grazing treatment with CSW. The PNM at 15–30 cm was greater in the chemical or mechanical than the grazing treatment in 2009 and 2011 and at 5–15 cm was greater with W–P/B–F than CSW in 2010. From 2009 to 2011, PON at 0–30 cm and PNM at 15–30 cm reduced from 2 to 580 kg N ha−1 year−1 in the grazing and chemical treatments, but the rate varied from −400 to 2 kg N ha−1 year−1 in the mechanical treatment. Lower amount of labile than nonlabile organic matter returned to the soil through feces and urine probably reduced soil active and coarse organic matter N fractions with sheep grazing compared to herbicide application and tillage for weed control. Reduction in the rate of decline in N fractions from 2009 to 2011 compared to the herbicide application treatment, however, suggests that sheep grazing may stabilize N fractions in the long-term if the intensity of grazing is reduced. Animal grazing may reduce soil N fractions in annual cropping systems in contrast to known increased fractions in perennial cropping systems

Crop yields and soil organic matter responses to sheep grazing in US northern Great Plains

Sheep (Ovis aries L.) grazing, a cost-effective method of controlling weeds compared to herbicide application and tillage, may influence soil C and N levels by consuming plant residue and returning feces and urine to the soil, but little is known about the practice on soil C and N storage under dryland cropping systems in the northern Great Plains, USA. Three weed control practices [sheep grazing (GRAZ), herbicide application (CHEM), and tillage (MECH)] and three cropping sequences [continuous alfalfa (Medicago sativaL.) (CA), continuous spring wheat (Triticum aestivum L.) (CSW), and spring wheat-pea (Pisum sativumL.)/barley (Hordeum vulgaris L.) hay mixture-fallow (W-P/B-F)] were evaluated on a Blackmore silt loam from 2009 to 2011 in southwestern Montana, USA. Crop yields and soil organic C (SOC), total N (STN), NH4-N, and NO3-N contents at the 0–120 cm depth were quantified. Annualized spring wheat grain and biomass (stems + leaves) yields and C and N contents were greater with CSW than with W-P/B-F, but hay biomass and C content were similar between CA and W-P/B-F. While C and N in aboveground biomass after spring wheat and hay harvest were removed through haying in CHEM and MECH, sheep grazing removed about 99% of these elements in GRAZ. The SOC and STN at 5–15 cm were greater with CSW or W-P/B-F than with CA in GRAZ and MECH, but SOC at 30–60 cm was greater with CA than with CSW in MECH. The NH4-N content at most depths varied among treatments and years, but NO3-N content at 5–120 cm was greater with CSW and W-P/B-F than with CA. Longer duration of sheep grazing during fallow periods due to increased return of C and N through feces and urine or residue incorporation to a greater depth probably increased soil C and N storage at the surface layer with CSW and W-P/B-F in GRAZ and MECH, but increased root biomass likely increased C storage at the subsurface layer with CA in MECH. Absence of N fertilization and/or greater N uptake probably reduced soil NO3-N level with CA than with other cropping sequences. Regardless of treatments, SOC and STN declined from 2009 to 2011, probably due to residue removal from haying and grazing. Moderate sheep grazing during fallow periods can be used to increase soil C and N storage, obtain farm C credit, and sustain dryland crop yields compared to herbicide application for weed control in the semiarid regions

Net Greenhouse Gas Emissions Affected by Sheep Grazing in Dryland Cropping Systems

Sheep (Ovis aries L.) grazing is an inexpensive method of weed control in dryland cropping systems, but little is known about its effect on net greenhouse gas (GHG) emissions. We evaluated the effect of sheep grazing compared with herbicide application for weed control on GHG (CO2, N2O, and CH4) emissions from May to October 2010 and 2011, net global warming potential (GWP), and greenhouse gas intensity (GHGI) in a silt loam under dryland cropping systems in western Montana. Treatments were two fallow management practices (sheep grazing [GRAZ] and herbicide application [CHEM]) and three cropping sequences (continuous alfalfa [Medicago sativa L.] [CA], continuous spring wheat [Triticum aestivum L.] [CSW], and spring wheat–pea [Pisum sativum L.]/barley [Hordeum vulgaris L.] hay–fallow [W-P/B-F]). Gas fluxes were measured at 3- to 14-d intervals with a vented, static chamber. Regardless of treatments, GHG fluxes peaked immediately following substantial precipitation (\u3e12 mm) and N fertilization mostly from May to August. Total CO2 flux from May to October was greater under GRAZ with CA, but total N2O flux was greater under CHEM and GRAZ with CSW than other treatments. Total CH4 flux was greater with CA than W-P/B-F. Net GWP and GHGI were greater under GRAZ with W-P/B-F than most other treatments. Greater CH4 flux due to increased enteric fermentation as a result of longer duration of grazing during fallow, followed by reduced crop residue returned to the soil and/or C sequestration rate probably increased net GHG flux under GRAZ with W-P/B-F. Sheep grazing on a cropping sequence containing fallow may not reduce net GHG emissions compared with herbicide application for weed control on continuous crops

Integrating Sheep Grazing into Cereal-Based Crop Rotations: Spring Wheat Yields and Weed Communities

Crop diversification and integration of livestock into cropping systems may improve the economic and environmental sustainability of agricultural systems. However, few studies have examined the integration of these practices in the semiarid areas of the Northern Great Plains (NGP). A 3-yr experiment was conducted near Bozeman, MT, to compare the effects of crop rotation diversity and weed management practices imposed during fallow periods [sheep (Ovis aries) grazing, reduced tillage, and conventional tillage] on spring wheat (Triticum aestivum L.) yields and weed pressure. Management treatments were applied to replicated whole plots, within which the split-plots received crop rotation treatments [continuous spring wheat (CSW) and a 3-yr rotation of annual forage, fallow, and spring wheat, where each phase was present in each year]. In the initial 2 yr, the realized rotational treatments were wheat–fallow and CSW. In the final year, wheat was grown following all phases of the diversified rotation. Yields were similar among management treatments within the wheat–fallow and CSW rotations. Weed pressure was generally low but perennial weeds were more abundant in grazing-managed, wheat–fallow systems. The integration of livestock into the annual hay crop–fallow–spring wheat rotation was associated with a nearly 30-fold increase in weed pressure and a yield reduction of 51.2% compared to conventional management. The results suggest that although targeted sheep grazing is a viable alternative to conventional fallow management in CSW and wheat–fallow rotations, successful integration of livestock in diversified cropping systems requires more effective weed management practices

Sheep Grazing Influence Soil Microbial and Particulate Organic Carbon in Dryland Cropping Systems

Sheep grazing may influence soil C fractions by consuming crop residue and weeds and returning C through feces and urine to the soil. We examined the effect of sheep grazing compared with tillage and herbicide application for weed control on soil microbial biomass C (MBC), potential C mineralization (PCM), and particulate organic C (POC) in relation to soil organic C (SOC) at the 0-30 cm depth in a Blackmore silt loam under dryland cropping systems from 2009 to 2011 in southwestern Montana, USA. Treatments were three weed management practices (sheep grazing [grazing], herbicide application [chemical], and tillage [mechanical]) and two cropping sequences (continuous spring wheat [CSW] and spring wheat-pea/barley mixture hay-fallow [W-P/B-F]). The MBC at 0-5 cm was greater in mechanical with CSW than grazing with CSW or mechanical with W-P/B-F in 2010 and 2011. Averaged across years, POC at 0-5 cm was greater in grazing than chemical with W-P/B-F, at 5-15 cm was greater in chemical than grazing with CSW, and at 15-30 cm was greater in grazing than chemical and mechanical with CSW. The PCM/SOC ratio at 15-30 cm was greater in mechanical than grazing with CSW. At all depths, MBC, PCM, and POC decreased from 2009 to 2011 regardless of treatments, except for MBC in mechanical with CSW at 0-5 cm which increased. Lower proportion of labile than nonlabile organic matter returned to the soil through feces and urine probably reduced microbial biomass and activity, but increased coarse soil organic matter with sheep grazing compared with herbicide application and tillage. Sheep grazing may improve soil health and quality in the long term by enhancing microbial biomass and C storage compared with tillage and herbicide application for weed control under dryland cropping systems

Forage Intake and Wastage by Ewes in Pea/Hay Barley Swath Grazing and Bale Feeding Systems

Harvested feed costs, particularly during the winter, are traditionally the highest input associated with a ruminant livestock operation. Although swath grazing has been practiced for over 100 years and literature exists for cattle use of swath grazing, no published results are available on use of swath grazing by sheep. Sixty mature, white-faced ewes were used in a completely randomized design repeated 2 years to evaluate whether feeding method (swath grazed or fed as baled hay in confinement) of intercropped field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) forage affected ewe ADG (average daily gain), forage DMI (dry matter intake), and wastage. The study was conducted at Ft. Ellis Research Station in Bozeman, MT during the summers of 2010 and 2011. Each year, 30 ewes were allocated to 3 confinement pens (10 ewes/pen) and 30 ewes were allocated to 3 grazing plots (10 ewes/plot). Ewes had ad libitum access to forage and water. Individual ewe forage DMI was estimated using chromic oxide (Cr2O3) as a marker for estimating fecal output. Measures of fecal output were combined with measures of forage indigestibility to determine DMI for each ewe. Forage wastage was calculated by sampling and weighing initial available forage, and subtracting final available forage and DMI. Forage DMI (P ≥ 0.13), ewe ADG (P≥ 0.40), and forage percent wastage (P \u3e 0.28) did not differ for swathed versus baled pea/hay barley forage during either year. These results suggest that a swathed feeding system can function as a viable alternative to a traditional baled feeding system for pea/hay barley forage in commercial sheep operations