Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 27, 2013
Publication Date: November 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/57554
Citation: Barsotti, J.L., Sainju, U.M., Lenssen, A.W., Montagne, C., Hatfield, P. 2013. Crop yields and soil organic matter responses to sheep grazing in U.S. northern Great Plains. Soil and Tillage Research. 134:133–141. Available: http://dx.doi.org/10.1016/j.still.2013.07.015. Technical Abstract: 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. Little is known about the effect of sheep grazing on soil C and N storage under dryland cropping systems in the northern Great Plains, USA. We studied the effects of fallow management practices for weed control [sheep grazing (GRAZ), herbicide application (CHEM), and tillage (MECH)] and 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 mixture-fallow (W-P/B-F)] on soil organic C (SOC), total N (STN), NH4-N, and NO3-N contents at the 0-120 cm depth and crop yields. The experiment was conducted in a Blackmore silt loam from 2009 to 2011 in southwestern Montana, USA. 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. 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 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. Sheep grazing had minor effect on crop yields and soil C and N levels compared to tillage and herbicide application for weed control.