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, w (,)l <=> ~ , "'"" Johnston (21), Rauzi (33), and Rhoades et al. (37) found significant differences in water intake rates on areas grazed at rates between light, moderate, and heavy intensity for periods of more than 20 years. Hanson et al. (18) found that after 26 years areas grazed heavily yielded significantly more runoff than those grazed moderately, and moderate grazing yielded significantly more runoff than from areas grazed only lightly. McCarty and Mazurak (29) reported significant increases in soil bulk density and decreases in total soil porosity on areas grazed at heavy-continuous and moderate-deferred-rotation rates over nongrazed areas after 25 years of treatment. B. Timing of Grazing or Rest Periods Martin (28) reported on data believed to support "the view that little benefit is gained by resting the range for only part of a normal grazing period." It was suggested that a grazing schedule for semi-desert ranges in Arizona should provide rest during 2 out of 3 years when plants are growing. It was also stated that a grazing system should, be designed to remove 40 percent of the perennial grass production. Smeins (38) believes that periodic, short term, and partial defoliation of plants may have beneficial effects on hydrologic processes as well as on vegetation. It was stated that a favorable forage resource may be maintained, erosion hazard not increased, and good quality runoff water possibly increased. Lusby (26) reported on data collected during two distinct study periods at Badger Wash, Colorado. In the first period (1953-65), heavy grazing by sheep and cattle occurred during the winter and spring (November 15 to May 15). Grazing by sheep in the second period (1966-73) was at a moderate level during the winter (November 15 to February 15). Rate of runoff and sediment loss were used as indicators of site stability. Sediment loss during the winter-sheep grazing was 29 percent less than that during the sheep-cattle winter-spring grazing and was somewhat less than that in areas completely removed from grazing for at least 20 years. The report concludes that moderate grazing during winter. is notsignifi- cantly more harmful than nongrazing. Heavy grazing (greater than 60 percent util ization) and grazing during spring when soil is moist are definitely detrimental. Discussion with Lusby (27) revealed that over- all, moderate winter grazing produced 10 percent more sediment loss than nongrazing. C. Range Condition (Plant Vigor, Density of Vegetal Ground Cover, Litter, Soil Tilth) Rauzi et al. (34) conducted water studies for several years on range- lands in the mixed-grass and tall-grass prairies in six Northern and Central Plains States, It was found that both live vegetation and litter were highly correlated with water intake rate. Soil structure was the most important soil influence on infiltration and was second in gen- eral importance after vegetation. It was stated that range condition is directly related to water intake. Good condition ranges had a higher herbage producti on, greater mul ch materi a 1 (1 itter), and a more crumoly or granular surface structure conducive to a high rate of water intake. :/ ~:i , , ':t , j . l' ,'j J A 5 t... ." .'" "-~.'-,~'-. " .- M.,~;~~._>"";&O>{ _ ~ ,