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Net Greenhouse Gas Emissions Affected by Sheep Grazing in Dryland Cropping Systems
Author(s) -
Barsotti Joy L.,
Sainju Upendra M.,
Lenssen Andrew W.,
Montagne Clifford,
Hatfield Patrick G.
Publication year - 2013
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2012.0386
Subject(s) - agronomy , greenhouse gas , grazing , loam , environmental science , sativum , soil water , biology , ecology , soil science
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 (CO 2 , N 2 O, and CH 4 ) 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 (>12 mm) and N fertilization mostly from May to August. Total CO 2 flux from May to October was greater under GRAZ with CA, but total N 2 O flux was greater under CHEM and GRAZ with CSW than other treatments. Total CH 4 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 CH 4 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.