Effects of Stocking Rate and Botanical Composition on the
Physical Characteristics of the Riparian Zones of Pastures
(A Two-Year Progress Report)
Grazing management practices that allow congregation of cattle near pasture streams may increase sediment, phosphorus, and pathogen loading of the streams by removing the vegetation and causing manure accumulation near the streams. To assess the effects of stocking rate and pasture characteristics on the risk of pollution of pasture streams, forage sward height, bare and manure-covered soil, and forage species were measured along the banks of streams in 13 pastures on 12 cow-calf operations in southern Iowa. Mean sward heights, and bare and manure-covered soil were different (P<0.0001) between the 13 pastures. There were also month differences for mean sward height and manure-covered ground (P<0.0001), but not for bare soil (P>0.05). The proportion of vegetation species as tall fescue, Reed canarygrass, or clover were different (P<0.03) between farms. The proportion of tall fescue, Reed canarygrass, Kentucky bluegrass and orchardgrass in the vegetation species were different (P<0.03) between months.
Farms with the least proportion of tall fescue and greatest proportion of Reed canarygrass had the least amount of bare soil within the riparian areas of pastures. Stepwise multiple regressions were calculated using vegetative species, and sampling interval and annual stocking rates of cattle on the 13 pastures. Sward height decreased as tall fescue, bluegrass and annual stocking of cow-days per acre increased and decreased as clover increased. The proportion of soil that was bare increased as the stocking rate per foot of stream increased and decreased as the proportion of Reed canarygrass and sedge increased. Manure-covered ground increased as the stocking rate per acre per sampling interval and the proportions of tall fescue and bluegrass in the vegetation increased, and decreased as broadleaf weeds and weed grasses increased. Increased stocking rates will result in decreases in forage sward height and increases in manure cover in riparian zones. The presence of tall fescue may also increase cattle activity near streams reducing sward height and increasing manure-covered soil in the riparian area.