• Prediction of leaf:stem ratio in grasses using near infrared reflectance spectroscopy

      Smart, A. J.; Schacht, W. H.; Pedersen, J. F.; Undersander, D. J.; Moser, L. E. (Society for Range Management, 1998-07-01)
      Leaf:stem ratio of grass stands is an important factor affecting diet selection, quality, and forage intake. Estimates of leaf:stem ratios commonly are based on a labor intensive process of hand separating leaf and stem fractions. Near infrared reflectance spectroscopy (NIRS) has been used successfully to predict forage quality and botanical composition of vegetation samples. The objective of this study was to evaluate the use of NIRS to predict leaf:stem ratios in big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L.), and smooth bromegrass (Bromus inermis Leyss.). A total of 72 hand-clipped samples of each species was taken from seeded monocultures in eastern Nebraska throughout the 1992, 1993, and 1994 growing seasons. Leaf:stem ratio was determined first for each sample and then the entire sample was ground. Samples were scanned by a Perstorp model 6500 near infrared scanning monochromator. Three calibration equations were developed based on using 18, 36, and 54 (1/4, 1/2, and 3/4 of total samples, respectively) samples. These 3 calibration equations were used to determine the number of samples necessary to achieve an r2 of 0.70 or higher for each data set. Big bluestem and switchgrass had coefficients of determination (r2) of less than or greater than 0.69 for all calibration equations except for the equation using only 18 samples of big bluestem r2 = 0.60). Smooth bromegrass had a r2 ranging from only 0.06 to 0.14 for the calibration equations regardless of the number of samples used. Near infrared reflectance spectroscopy was a rapid means of estimating leaf:stem ratios in monocultures of big bluestem and switchgrass but it was not suitable for smooth bromegrass.
    • Soil depth assessment of sagebrush grazing treatments using electromagnetic induction

      Bork, E. W.; West, N. E.; Doolittle, J. A.; Boettinger, J. L. (Society for Range Management, 1998-07-01)
      Depth to a root restricting layer affects both soil moisture and nutrient availability, resources strongly correlated to plant cover and production. We evaluated the potential of 2 electromagnetic induction meters (EM38 and EM31) for non-destructively assessing soil depth to bedrock in 2 long-term seasonal sagebrush steppe sheep grazing treatments with different vegetational compositions. Apparent conductivity readings, measured with the EM38 and EM31 in both the horizontal (H) and vertical (V) dipole orientations, were positively related to soil depth. Apparent conductivity measured with the EM31H (r2 = 0.78) and EM38V (r2 = 0.75) were the best predictors of depth. Soil depth distributions were similar between grazing treatments based on Kolmogorov-Smirnov (K-S) tests of the EM38H apparent conductivity (P = 0.47) and EM38V apparent conductivity (P = 0.56). In constrast, K-S tests for the EM31H apparent conductivity (P = 0.09) and EM31V apparent conductivity (P < 0.01) indicated the fall-grazed treatment had a larger area in which soil depth exceeded 150 cm. Because less than 2% of each grazing treatment was predicted to have soils deeper than 150 cm, however, overall site differences between the 2 treatments appeared to be minor. Therefore, the vegetational differences between the treatments have probably resulted more from differences in the seasonality of grazing rather than ecological site characteristics as reflected in soil depth. Maps of soil depth indicated both treatments consisted of intermittent shallow and deep soils, created by several parallel basalt pressure ridges. Results suggest electromagnetic induction can effectively assess the spatial variability of soil depth and could aid in selecting sites for rangeland monitoring or manipulation.
    • Spatial memory and food searching mechanisms of cattle

      Laca, E. A. (Society for Range Management, 1998-07-01)
      Uneven distribution of grazing negatively impacts rangelands through over- and under utilization of resources. The goal of this study was to quantify the role of experience on search pattern and foraging efficiency of cattle. Steers (Bos taurus x B. indicus) were exposed once daily during 15-20 min. sessions to 3 food-distribution treatments: VR (variable-random, food locations were changed randomly and daily), CR (constant-random, food locations were randomly set at the beginning and remained the same throughout the experiment), and CC (constant-clumped, food locations were constant and clumped in groups of 5). Pelleted feed was available in 20 out of 64 feeders arranged in 8 rows and 8 columns, with neighboring locations 5 m apart. Encounter rate of food locations was partitioned into search speed, total number of visits per unit distance walked, ratio of different (not previously visited within the session) locations to total visits (including revisits), and ratio of food locations to different locations visited. Intake rate increased (P < 0.01) as animals gained experience, but more slowly in variable-random than constant-clumped and constant-random. Residence time at food locations declined (P < 0.01) with increasing experience. Intake rate was negatively affected (P < 0.01) by search time per food location, which in turn was determined by the steers' ability to remember food locations. Steers in constant random and constant clumped used long-term spatial memory to return to food locations, and ignored areas where no food was found (P < 0.01). Conversely, steers in variable random used a strategy based on avoidance of locations already visited within sessions. Thus, in constant random and constant clumped food search was more efficient (P < 0.01) and concentrated in certain areas, whereas in variable random it was less efficient and more evenly distributed over the whole area. The results of this study suggest that impeding spatial memory could improve grazing patterns.
    • Temperature effects on regrowth of 3 rough fescue species

      King, J. R.; Hill, M. J.; Willms, W. D. (Society for Range Management, 1998-07-01)
      Three species of rough fescue, alpine rough fescue (Festuca altaica Trin.), mountain rough fescue (F. campestris Rydb.), and plains rough fescue (F. hallii (Vasey) Piper) were grown for 12 weeks under 5 temperature regimes — 7:3, 12:8, 17:13, 22:18, and 27:23 degrees C — and defoliated 3 times to 3.5 cm at 4-weekly intervals in a growth cabinet study. Final plant dry mass and harvestable biomass production were greatest at 17:13 degrees C for alpine rough fescue and plains rough fescue, and at 12:8 degrees C for mountain rough fescue. Harvestable biomass plateaued or declined at the final harvest in all species for temperatures above 12:8 degrees C. Tiller numbers increased at successive harvests. Biomass per tiller declined markedly at the final harvest of alpine rough fescue at all temperatures. Regrowth in alpine rough fescue was markedly reduced at temperatures either above or below the optimum. The results indicate that mountain rough fescue and plains rough fescue are better able to regrow following defoliation at temperatures below or equal to their optima, than at temperatures above their optima. This provides greater understanding of field responses in both species where frequent defoliations are more deleterious after the April/May period when temperatures are above optimal.
    • Using a grazing pressure index to predict cattle damage of regenerating tree seedlings

      Pitt, M. D.; Newman, R. F.; Youwe, P. L.; Wikeen, B. M.; Quinton, D. A. (Society for Range Management, 1998-07-01)
      This research investigated the potential for using cattle grazing pressure (AU Mg-1 ha-1) and stocking rate (Animal Unit Days ha-1) for predicting basal scarring and browsing of lodgepole pine (Pinus contorta Dougl.) seedlings on cutblocks in southern British Columbia from 1989 to 1992. Cattle browsing on lodgepole pine seedlings occurred almost exclusively during the first 2 years of grazing. Browsing increased (P < 0.05; r2=0.71) with increasing stocking rate only during the first year of grazing. Browsing increased with increasing grazing pressure in 1989 (P < 0.05; r2= 0.38) and 1990 (P < 0.05; r2 = 0.39). Basal scarring peaked during the second year of grazing, but was correlated (P < 0.05; r2 = 0.79) with stocking rate only during the first year of grazing. Increasing grazing pressure was associated with higher (P < 0.05) basal scarring during all 4 years of the study, and likely better predicts trampling damage than does stocking rate, particularly during the first year of grazing. Basal scarring during 1989 generally increased to > 10% of sample trees when grazing pressure exceeded 12.0 AU Mg-1 ha-1. This threshold grazing pressure value of 12.0 AU Mg-1 ha-1, however, cannot likely be extrapolated directly to other sites. Grazing pressure values and associated basal scarring are unquestionably influenced by many factors (e.g., pasture size, kind of grazing animal, forage species, tree height, water availability, topography, and weather patterns during the grazing period). Nonetheless, our work provides evidence that grazing pressure provides a useful index for predicting the potential for trampling damage of lodgepole pine seedlings by cattle.
    • Viewpoint on objectives, boundaries, and rangeland carrying capacity

      Scarnecchia, David L. (Society for Range Management, 1998-07-01)
      This paper de-analyses a recent paper by Roe (1997, J. Range Manage., 50:467-472) entitled Viewpoint: On Rangeland Carrying Capacity. This response to that paper: (1) examines and demonstrates the importance of defining objectives and boundaries in management, science, management science and art, (2), reaffirms an earlier, objective-based concept of carrying capacity applicable to general systems and to models of them, and (3) implores minimal use of unnecessary jargon in range management science.
    • Viewpoint: Applying riparian buffers to Great Plains rangelands

      Dosskey, M. G. (Society for Range Management, 1998-07-01)
      Better management of riparian areas has been promoted by public agencies for almost 2 decades. Recently, however, efforts have been intensified because serious conservation concerns remain. To achieve mandated conservation goals for water quality and wildlife will require widespread acceptance and application of recommended riparian practices. Success of riparian programs in the Great Plains will require recognition of differences between the interests of public agencies and those of private landowners and the development of an approach to riparian management that can accommodate both.