Douglas A. Bear

Stocking Rate and Riparian Vegetation Effects on Physical Characteristics of Riparian Zones of Midwestern Pastures

Abstract Grazing at high stocking rates may increase sediment and nutrient loading of pasture streams through transport in precipitation runoff and bank erosion. A 3-yr (2007–2009) grazing study was conducted on 13 cool-season grass pastures to quantify effects of stocking rate and botanical composition on forage sward height, proportions of bare and manure-covered ground, and bank erosion adjacent to streams. Pastures ranged from 2 ha to 107 ha with stream reaches of 306 m to 1 778 m that drained watersheds of 253 ha to 5 660 ha. Bare and manure-covered ground were measured at a 15.2-m distance perpendicular to the stream at 30.5-m intervals at up to 30 locations on each side of the stream by the line transect method in May, July, September, and November of each year. At the midpoint of the 15.2-m line, forage sward height was measured with a falling plate meter (4.8 kg · m−2) and plant species identified. In November 2006, fiberglass pins (1.6 × 76.2 cm) were driven 73.7 cm into the stream bank at 1-m intervals from the streambed to the top of the bank along 10 equidistant transect locations on each side of the stream to measure bank erosion during spring, summer, and fall of each year. Increasing pasture stocking rates increased manure-covered ground and decreased sward height, but did not affect proportions of bare ground. The greatest, intermediate, and least net soil erosion rates occurred during the winter/early spring, late spring/early summer, and late summer/fall seasons. Stocking rates between measurements, expressed as cow-days · m−1 stream, were not related to bank erosion. Increasing stocking rates per unit of stream length will increase manure cover and decrease forage sward height, but not affect proportions of bare ground or bank erosion rates adjacent to pasture streams. Therefore, managing stocking rates may reduce nutrient loading of pasture streams.

Stream Bank Erosion as a Source of Sediment and Phosphorus in Grazed Gastures of the Rathbun Lake Watershed in Southern Iowa, United States

Livestock grazing of riparian areas can have a major impact on stream banks and stream integrity if improperly managed. The goals of this study were to determine the sediment and phosphorus (P) losses from stream bank soils under varying cattle stocking rates and to identify additional factors that impact stream bank erosion in the southern Iowa Drift Plain. The research was conducted on 13 cooperating beef cow-calf farms within the Rathbun Lake Watershed in south central Iowa. Over three years, stream bank erosion rates were estimated by using an erosion pin method. Eroded stream bank lengths and area, soil bulk density, and total P (TP) content in stream bank soil were measured to calculate soil and TP losses via stream bank erosion. The length of severely eroded stream banks and soil compaction of the riparian areas of the pastures were positively related to stocking rates. There was no direct relationship between bank erosion and stocking rate. These results suggest that use of riparian areas as pasture can negatively impact the integrity of the major source areas and that the impact could be reduced through management of livestock stocking densities within these riparian areas.

Physical Characteristics, Shade Distribution, and Tall Fescue Effects on Cow Temporal/ Spatial Distribution in Midwestern Pastures

Abstract Nonpoint source (NPS) pollution of water resources may occur from congregation of cattle near streams or ponds. Therefore, relationships of physical characteristics, shade distribution, and tall fescue (Festuca arundinacea Schreb.) prevalence in cool-season grass pastures to the temporal/spatial distribution of grazing cattle were evaluated in two studies on beef cow/calf farms. Global positioning system (GPS) collars recorded the location of 2–3 cows per pasture at 10-min intervals for 5–14 d in the spring, summer, and fall annually. Pasture botanical composition was visually assessed annually. In Study 1, cow location was recorded on five pastures ranging in size from 13 ha to 125 ha with 1.9–3.8% of the pasture area in a stream or pond (water source) and 2–30% of the pasture area within 30.5 m of the water source (waterside zone) for 3 yr. Shade covered 27–73% of the pasture area with 3–64% of shade located within waterside zone. In Study 2, cow location was recorded in three pastures with areas of 8 ha, 10 ha, and 15 ha with 17.8%, 43.4%, and 14.7% of the total area and 28%, 73%, and 68% of the total shade in the waterside zone for 1 yr. In Study 1, proportions of cow observations within the waterside zone increased with decreasing pasture area (r2 = 0.61) and increasing proportions of the total pasture area (r2 = 0.37) and shade (r2 = 0.29) within the waterside zone. In Study 2, proportion of cow observations in the waterside zone increased as the proportion of total area (r2 = 0.62) and shade (r2 = 0.42) in the waterside zone increased. Results imply more restrictive measures to minimize the risks of NPS pollution of water resources may be most effective in smaller and narrow pastures. Resumen La contaminación de origen no identificado (NPS) de los recursos hídricos, puede ocurrir debido a la congregación del ganado cerca de los arroyos o estanques. Por lo tanto, las relaciones de las características físicas, distribución de la sombra y la incidencia de Festuca alta (Festuca arundinacea Schreb.) en potreros con gramíneas de crecimiento invernal en la distribución temporal/espacial del pastoreo del ganado se evaluaron en dos estudios en una granja de vaca-becerro. Collares de sistema de posicionamiento global (GPS) registraron la ubicación de 2 a 3 vacas por potrero a intervalos de 10 minutos de 5 a 14 en la primavera, verano y otoño anualmente. La composición botánica de los potreros se evaluó visualmente cada año. En el estudio 1, conducido durante tres años, la ubicación de las vacas se registró en cinco potreros con un rango de 13 a 125 hectáreas de extensión, con 1.9 a 3.8% de la superficie del potrero en arroyos o estanques (fuente de agua) y 2 a 30% de la superficie del potrero dentro de 30.5 m de distancia de la fuente de agua (zona de agua) para 3 años. Los sombreaderos cubrieron de 27 a 37% del área del potrero con 3 a 64% de la sombra ubicada dentro de la zona del agua. En el estudio 2, la ubicación de las vacas se registró en tres potreros con áreas de 8, 10, y 15 hectáreas con 17.8, 43.4 y 14.7% de la superficie total y 28, 73 y 68% de la sombra total en la zona del agua y se evaluó durante un año. En el estudio 1, las proporciones de las observaciones de las vacas dentro de la zona del agua aumentaron con la disminución de la superficie del potrero (r2 = 0.61) y aumentaron las proporciones de la superficie total del potrero (r2 = 0.37) y con la sombra (r2 = 0.29) dentro de la zona del agua. En el estudio 2, aumento la proporción de observaciones de vaca en la zona del agua conforme la proporción de la superficie total (r2 = 0.62) y sombra (r2 = 0.42) en la zona del agua aumentó. Estos resultados sugieren medidas más preventivas para minimizar los riesgos de contaminación de NPS en los recursos hídricos y puede ser más eficaz en potreros más estrechos y pequeños.