Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 10, 2012
Publication Date: N/A
Technical Abstract: Sheep grazing to control weeds during fallow may influence soil greenhouse gas (CO2, N2O, and CH4) emissions by consuming crop residue and returning feces and urine to the soil. An experiment was conducted to evaluate the effect of sheep grazing compared to herbicide application on soil temperature and water content at the 0-15 cm depth and greenhouse gas emissions from May to October, 2010 and 2011 under dryland cropping systems in western Montana, USA. Treatments were two fallow management practices (sheep grazing [grazing] and herbicide application [chemical]) and three cropping sequences (continuous alfalfa [CA], continuous spring wheat [CSW], and spring wheat-pea/barley hay-fallow [W-P/B-F]). Soil temperature and water content and greenhouse gas concentrations were measured at 3 to 14 d intervals with a vented, static chamber. Soil temperature and water content were greater in the chemical with W-P/B-F and grazing with CA than in other treatments. Greenhouse gas fluxes peaked immediately following substantial precipitation (>12 mm) and/or N fertilization, regardless of treatments, with most of the fluxes occurring from May to July. Total CO2 flux from May to October was greater in the grazing with CA but total N2O flux was greater in the chemical and grazing with CSW than in other treatments in 2010 and 2011. Total CH4 flux was greater in CA than in CSW and W-P/B-F in 2011. Return of C to the soil through sheep feces and urine, followed by greater root respiration, probably increased CO2 flux during grazing in alfalfa. Increased N fertilization rate to sustain crop yields probably increased N2O flux in the grazing and chemical treatments with continuous spring wheat. Non-N fertilization, however, likely increased CH4 flux under alfalfa compared to other cropping sequences. Less intensive sheep grazing to control weeds with reduced rate of N fertilization to crops may be used to mitigate greenhouse gas emissions under dryland cropping systems.