Animal Industry Report

Extension Number

ASL R2779



Summary and Implications

South central Iowa grasslands are dominated by cool season grass species with low productivity and plant species diversity which limits the forage for grazing animals and habitat for native grassland wildlife. Strategic spring mobgrazing may reduce competition from cool-season grass species allowing legumes, early successional species, and native plants to establish while improving soil characteristics. Two blocks of three replicated pastures were divided into 5 equal-sized paddocks to determine the effects of early spring mob-grazing on pasture forage and soil characteristics. In each pasture, one paddock was not grazed (U) and 4 were strip- (S; moved once per day with a back fence) or mob- (M; moved 4 times per day with a back fence) grazed beginning in May of 2011 (BL1) and 2012 (BL2) by 10 cows at a live forage DM allowance of 2% BW/d. Subsequently, one mob (MR) and strip (SR) paddock in each pasture was rotationally stocked to remove 50% of the live forage with 35-d rest periods beginning 60 d after spring grazing in yr 1 of each block. Measurements includedwater infiltration determined with double ring infiltrometers, soil penetration resistance determined with a penetrometer, pasture botanical composition determined by the line transect method, and ground nesting bird habitat measured as visual obstruction to a 3.3x 3.3 ft board by image analysis of digital photos. In BL1, there were no significant differences in water infiltration or penetration resistance between treatments in 2011. The proportions of annual grasses and bare ground were greater (P< 0.05) in grazed than U paddocks in July 2011. In 2012, the proportions of legumes were greater (P< 0.05) in M and SR paddocks in May and in M, S, and SR paddocks in July than U paddocks. In BL2, proportions of annual grasses in M and S paddocks and bare ground in MR, S, and SR paddocks were greater (P< 0.05) than U paddocks in July 2012. In 2011, visual obstruction to 1 m was greater (P< 0.05) in U than grazed paddocks of BL1 in July. However, in October, visual obstruction did not differ between S and U paddocks to 19.7 in. and was greater (P< 0.05) in S and M than SR and MR paddocks to a height of 15.7 in.

Copyright Holder

Iowa State University