Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2005
Publication Date: 2/1/2007
Citation: Hatfield, P.G., Lenssen, A.W., Spezzano, T.M., Blodgett, S.L., Goosey, H.B., Kott, R.W. 2007. Incorporating sheep into dryland grain production systems: II. impact on changes in biomass and weed density. Small Ruminant Research. 67(2-3):215-221. Interpretive Summary: Weed control is the single largest cost for Montana producers using summer fallow for dryland cereal production. We conducted field trials comparing sheep grazing to tillage, burning, and untreated controls for effects on weed density and aboveground biomass. Sheep grazing provided good control of weeds. Reduction of aboveground biomass, important for protection of soil from wind and water erosion, was generally similar to that from burning or tillage.
Technical Abstract: Weed control in fallow management to conserve soil moisture and nutrients is the largest variable cost to dryland grain production. Our objective was to compare burning, grazing, tilling, trampling and clipping wheat stubble fields on changes in total aboveground biomass and weed density in summer fallow. Treatments were evaluated in three experiments using a randomized complete block design for each experiment with four replications at each site. Eight, six, and two sites were used for Experiments 1, 2, and 3, respectively. For Experiment 1, treatments were fall tilled (GT), fall grazed (GF), spring grazed (GS), fall and spring combined grazed (GFS), and an untreated control (GC). For grazing treatments, five mature ewes were confined with electric fence to each plot for 24 hr for GF and GS resulting in a stocking rate of 400 sheep d/ha. For GFS the stocking rate was 800 sheep d/ha. For Experiment 2, treatments were fall grazed (BF), fall burned (BB), fall tilled (FT), and an untreated control (BC). In Experiment 3, treatments were fall trampling by sheep (TF), spring trampling by sheep (TS), fall and spring trampling by sheep (TFS), hand clipping to a stubble height of 4.5 cm (TCP), and an untreated control (TC). Trampling treatments were applied at the same stocking rates as grazing treatments but sheep were muzzled to prevent intake. Data were collected in the fall, prior to treatment imposition, and spring, after treatments had been removed. In Experiment 1, post treatment biomass and weed density were lower (P<0.01) at all sites for the mean of the grazed treatments compared to GC. The mean of the grazed treatments did not differ (P>0.13) from GT for post treatment biomass or change in weed density at six of the eight sites and three of the four sites, respectively. In Experiment 2, percent change (reduction) in biomass did not differ (P>0.15) between BB and BF at five of the six sites. Reduction in weed density did not differ (P=0.63) between fall burning and fall grazing at one site, but at the second site reduction in weeds was greater (P=0.08) for burning than grazing. In Experiment 3, the trample treatments resulted in a greater (P < 0.07) reduction in biomass than TC and TCP at both, and one of the two sites, respectively. No differences (P > 0.10) in weed density were detected. These results indicate the potential for using grazing sheep as a component in fallow management to reduce biomass and control weeds.