The Relationship of Herbage Mass and Characteristics to Animal Responses in Grazing Experiments

Caucasian bluestem [Bothr&xhloa tmucaka (Trln.) C.E. Hubb.] ls a warm-aeaaon grass introduced from Eurasia that is currently used for reseeding rangelands in the southern Great Plahts. Although this species is thought to be graaing tolerant, no specific information is available concerning its response to gradng. This study was conducted to evaluate the effect of 2 levels of grazing on xylem water potential ($) and total leaf conductance (IT) of Caucasian blueatem. During the grazing period (mid May to mid September) diurnal tj and gT measurements were made on 3 days in 1983 and 1984, and afternoon measurements were taken at weekly intervals ln 1984. Soil moisture at 15,45, and 75 cm depths was monitored in 1984. Heavily graaed plants exhibited consistently higher (less negative) $, and generally higher gT than lightly grazed plants. Averaged over the season, heavy graxing increased mean afternoon 1,4 and gT by 28 and 7646, respectively, compared to light grazing. Soil moisture was conserved with heavy graaing; treatment differences were greatest during July, which is generally the driest summer month in central Oklahoma. Thus, for Caucasian bluestem, leaves from heavily graxed swards were under less water stress than Ieavea from lightly graaed swards.

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Grazing Effects on Water Relations of Caucasian Bluestem

Compromises in the Design and Conduct of Grazing Experiments

Caucasian bluestem (Bothrioctrlocr coueosieo (Trin.) C.E. Hubb.) is a warm-season grass introduced from Eurasia that is currently used for reseeding farmland and depleted range in the Southern Great Plains. Although this species is thought to be grazing tolerant, little specific information is available concerning its response to grazing. Variable (put-and-take) stocking was used to maintain heavy (3 to 8 steers/ha) and light (2.5 to 4.5 steers/ha) grazing treatments during mid May to late September from 1983 to 1985. Seasonal changes in root mass and root length to a depth of 60 cm were measured the first 2 years, and end-of-season root length was measured the third year. Leaf area index (LAI) was measured during the first 2 years. Peak root mass was 27 and 46% less in heavily relative to lightly grazed swards in 1983 and 1984, respectively. Total root length for heavily grazed swards was 33 and 45% less than lengths of lightly grazed swards in 1983 and 1984, respectively. Heavy grazing resulted in a relatively larger reduction in LA1 than in either root mass or length, and thus the ratio of absorbing root surface to transpiring leaf surface was greater for heavily grazed than lightly grazed plants. This increased ratio may explain our previous observation that heavy grazing resulted in an improved water status of leaf tissue. End-of-season total root length over the 3-year period (15 to 18 and 24 to 28 km/m2 for heavily and lightly grazed swards, respectively) was remarkably consistent given the variable climatic conditions over the study period.

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The influence of grazing pressure on rooting dynamics of Caucasian Bluestem.

Pastures, forages, and grasslands dominate the landscape across the United States and support a large ruminant population that supplies the nation with value-added animal products. A historical perspective is presented of the innovations as they occurred in the Journal of Animal Science over the past 100 yr in pasture and forage research. Consideration was given to both animal and pasture perspectives. Areas given consideration from the animal perspective were schemes for feedstuff analysis, experimental design and statistics, forage sample preservation, indirect methods of measuring intake and digestion, TDN and energy, nutritive value, harvested forage, and innovations in the grazing environment. Areas given consideration from the forage perspective were a framework for forage-animal interface research, determining pasture yield, choice of stocking method, grazing management, partitioning of forage DM, near-infrared reflectance spectroscopy technology, antiquality constituents, and forage sample preservation. Finally, the importance was discussed of applying research results from the forage-animal interface to general ruminant nutrition research beyond the interface that is focused on altered diets.

ASAS Centennial Paper: utilization of pasture and forages by ruminants: a historical perspective.

Pasture experiments may be grazed using either variable (put-and-take) or fixed stocking rates. Considerations such as the risks of introducing bias, the reliability of the data, and the resources required for these methods of grazing are discussed, and criteria are described for choosing between the methods.

R. D. Mochrie

Papers

The Choice of Fixed or Variable Stocking Rates in Grazing Experiments

Comparison of set-stocked and put-and-take systems with growing heifers grazing Coastal Bermuda grass (Cynodon dactylon L. Pers).