Influence of off-stream supplements on streambanks of riparian pastures

Accelerated erosion of streambanks in grazed riparian pastures is of concer n to land managers. We tested the hypothesis that providing cattle free-cho ice off-stream water and trace mineralized salt would lessen negative impac ts of grazing on cover and stability of streambanks compared to pastures la cking these amenities, and may therefore reduce the potential of accelerate d erosion. The study was conducted on Milk Creek at the Hall Ranch Unit of the Eastern Oregon Agricultural Research Center near Union, Ore. Three repl ications each of 3 grazing treatments were examined: (1) non-grazed control ; (2) grazed with supplemental water and trace mineralized salt provided (" supplemented"); and (3) grazed with no supplemental water or salt ("non-sup plemented"). Each grazed pasture (approximately 12 ha) was stocked with cow -calf pairs for a mean stocking rate of 0.8 ha per AUM to achieve moderate grazing intensity of approximately 50% utilization of key forages. Pastures were grazed for 42 consecutive days during each of 2 years (1996-1997) beg inning mid-July. Estimates of streambank cover ("covered" or "uncovered") a nd stability ("stable" or "unstable") were taken before (June) and after (S eptember) grazing by examining 0.5 x 0.3 in plots placed on the greenline. Additionally, frequency of cattle hoof prints (number of plots with hoof pr ints/total number of plots) was measured as an indication of cattle presenc e in the greenline. Treatment effects were compared using one-way ANOVA. St reambank effects were consistent with observations of cattle distribution, with 26% of the streambank in supplemented pastures showing cattle presence (hoof prints), versus 31% for nonsupplemented pastures. Off-stream water a nd salt attracted cattle into the uplands enough to significantly (p less t han or equal to 0.05) reduce development of uncovered and unstable streamba nks from 9% in non-supplemented pastures to 3% in supplemented pastures. An "erosion index" indicated no significant (p < 0.05) difference in potentia l accelerated streambank erosion between supplemented and non-supplemented pastures.