Beyond grazing, managed grasslands provide ecological services that may offer economic incentives for multifunctional use. Increasing biodiversity of plant communities may maximize net primary production by optimizing utilization of available light, water, and nutrient resources; enhance production stability in response to climatic stress; reduce invasion of exotic species; increase soil OM; reduce nutrient leaching or loading in surface runoff; and provide wildlife habitat. Strategically managed grazing may increase biodiversity of cool-season pastures by creating disturbance in plant communities through herbivory, treading, nutrient cycling, and plant seed dispersal. Soil OM will increase carbon and nutrient sequestration and water-holding capacity of soils and is greater in grazed pastures than nongrazed grasslands or land used for row crop or hay production. However, results of studies evaluating the effects of different grazing management systems on soil OM are limited and inconsistent. Although roots and organic residues of pasture forages create soil macropores that reduce soil compaction, grazing has increased soil bulk density or penetration resistance regardless of stocking rates or systems. But the effects of the duration of grazing and rest periods on soil compaction need further evaluation. Because vegetative cover dissipates the energy of falling raindrops and plant stems and tillers reduce the rate of surface water flow, managing grazing to maintain adequate vegetative cover will minimize the effects of treading on water infiltration in both upland and riparian locations. Through increased diversity of the plant community with alterations of habitat structure, grazing systems can be developed that enhance habitat for wildlife and insect pollinators. Although grazing management may enhance the ecological services provided by grasslands, environmental responses are controlled by variations in climate, soil, landscape position, and plant community resulting in considerable spatial and temporal variation in the responses. Furthermore, a single grazing management system may not maximize livestock productivity and each of the potential ecological services provided by grasslands. Therefore, production and ecological goals must be integrated to identify the optimal grazing management system.

I would like to express my deepest gratitude to my major professor, Dr. James Russell, for the opportunities, guidance, and mentorship. Thank you for allowing me to pursue an M. S. in both animal nutrition and co-M. S. in environmental sciences concurrently which allowed me to develop a deeper understanding for the inextricable links between livestock production and grassland ecosystems. I would also like to thank my graduate committee members, Dr. Thomas Isenhart, and Dr. Daniel Morrical for their guidance and feedback throughout my graduate experience. The assistance, insight, and comic relief provided by the farm crews including Jim Dahlquist at Iowa State Beef Nutrition Farm and Kevin Maher and Nick at the McNay Memorial Research and Education Farm during many long days of field research was greatly appreciated. I would also like to thank my fellow graduate students including Kirk Schwarte, Doug Bear, Margarett Dunn, and Laura Daniels for their valuable discussions, assistance in completion of my work, and your friendship and support. I would also like to express my gratitude to all of the undergraduate students who have assisted with my research. Your hard work and dedication, even in less than optimal weather conditions, have made my research possible. I would also like to thank my family and friends. Particularly my parents, Joe and Jackie Bisinger, who provided me with endless encouragement and inspiration to achieve my goals and developing in me the work ethic and persistence which made this work possible. To my sister and her family, I would also like to send appreciation, for listening and helping me through all of my highs and lows during this journey. Finally, I would like to extend my appreciation to all of iv my friends which have provided support and to put everything into perspective, particularly Ray and Belinda Smalley and others I have met through being involved with the horse industry. "You can't prepare for everything life's going to throw at you. And you can't avoid danger. It's there. The world is a dangerous place, and if you sit around wringing your hands about it, you'll miss out on all the adventure."

For 2 grazing seasons, effects of pasture size, stream access, and off-stream water on cow distribution relative to a stream were evaluated in six 12.1-ha cool-season grass pastures. Two pasture sizes (small [4.0 ha] and large [12.1 ha]) with 3 management treatments (unrestricted stream access without off-stream water [U], unrestricted stream access with off-stream water [UW], and stream access restricted to a stabilized stream crossing [R]) were alternated between pasture sizes every 2 wk for 5 consecutive 4-wk intervals in each grazing season. Small and large pastures were stocked with 5 and 15 August-calving cows from mid May through mid October. At 10-min intervals, cow location was determined with Global Positioning System collars fitted on 2 to 3 cows in each pasture and identified when observed in the stream (0-10 m from the stream) or riparian (0-33 m from the stream) zones and ambient temperature was recorded with on-site weather stations. Over all intervals, cows were observed more (P ≤ 0.01) frequently in the stream and riparian zones of small than large pastures regardless of management treatment. Cows in R pastures had 24 and 8% less (P < 0.01) observations in the stream and riparian zones than U or UW pastures regardless of pasture size. Off-stream water had little effect on the presence of cows in or near pasture streams regardless of pasture size. In 2011, the probability of cow presence in the stream and riparian zones increased at greater (P < 0.04) rates as ambient temperature increased in U and UW pastures than in 2010. As ambient temperature increased, the probability of cow presence in the stream and riparian zones increased at greater (P < 0.01) rates in small than large pastures. Across pasture sizes, the probability of cow presence in the stream and riparian zone increased less (P < 0.01) with increasing ambient temperatures in R than U and UW pastures. Rates of increase in the probability of cow presence in shade (within 10 m of tree drip lines) in the total pasture with increasing temperatures did not differ between treatments. However, probability of cow presence in riparian shade increased at greater (P < 0.01) rates in small than large pastures. Pasture size was a major factor affecting congregation of cows in or near pasture streams with unrestricted access.

and Implications Soil compaction was measured as soil bulk density to a depth of 3 inches and soil penetration resistance to a depth of 6 inches at distances of 10 to 300 feet from a water source in pastures grazed by continuous, rotational or paddock strip-stocking at a stocking rate of 0.8 cows per acre over 3 years. Soil bulk density and penetration resistance 10 feet from the water source were greater than measurements further from the water sources. While stocking system had no main effects on soil bulk density and penetration resistance, paddocks grazed by stripstocking had lower penetration resistance at depths of 0, 5, and 6 inches than continuous stocked pastures in October of each year. Results imply that producers should avoid placing of congregation areas like water sources in areas that would be sensitive to soil erosion and nutrient run off. Use of stocking systems like paddock strip stocking that provide long rest periods may be somewhat helpful in maintaining plant growth and water infiltration in pastures.

Justin Bisinger, graduate assistant; Jim Russell, professor of animal science Summary and Implications Cattle congregating near pasture streams decrease forage sward height and root mass and increase fecal cover, thereby, increasing the risk of sediment, nutrient, and pathogen loading of the streams. Restricting stream access to stabilized crossings or offering off-stream water may decrease the time cattle spend near or in pasture streams, in turn reducing the risk of water quality impairment. However, the effectiveness of these management practices may be affected by pasture size. In a two-year study, six 30acre cool-season grass pastures bisected by a 475-ft stream reach on the Rhodes Research Farm were used to analyze the effects of pasture size on the efficacy of restricted stream access or off-stream water to alter the spatial/ temporal distribution of grazing cows in and near the pasture stream. Three grazing management treatments: unrestricted stream access without off-stream water (CSU), unrestricted stream access with off-stream water (CSUW), and restricted access to 16-ft wide stabilized crossings (CSR) were compared in two pasture sizes (10 and 30 acres) in five 4-week intervals with 2-week periods between May 18 and October 12 in 2010 and May 18 to October 8 in 2011. Five and fifteen fall-calving Angus cows were continuously stocked in each small and large pasture, respectively. At the beginning of each period two to three cows were fitted with GPS collars that recorded cow position every 10 minutes. Cows in small pastures with unrestricted stream access with or without off-stream water spent more (P<0.05) time in stream (0 to 16 feet from stream) and streamside (16 to 118 feet from stream) zones in small treatments than large treatments. Restricting stream access to stabilized stream crossings reduced the time cows spent in the stream and streamside zones compared to unrestricted stream access in small and large treatments. Regardless of pasture size, off-stream water had little effect on cow presence in the stream zone.