Graduate Thesis Or Dissertation
 

Vegetation and animal responses to grazing crested wheatgrass at three intensities and two seasons in southern Idaho

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  • Land useable for livestock grazing in the western United States is diminishing because of spreading municipalities, irrigation developments, highway construction, recreational demands and withdrawals. Concurrently, the demand for livestock and livestock products is increasing because of a rapidly growing population. As a result, production from the grazing land that remains must be increased to satisfy the increased wants of the population. Artificial seeding is improving the forage productivity on large areas of low producing range land in the Intermountain region. Methods of successfully establishing stands of forage plants by artificial means are reasonably well understood, but less information is available about grazing practices that will optimize the returns from these range improvement programs. A nine-year (1957-1965) grazing study was conducted on a crested wheatgrass (Agropyron cristatum and A. desertorum) seeding near Malta, Idaho for the purpose of evaluating plant and animal responses under three intensities of grazing (light, moderate or heavy) in two seasons (spring or fall). With the information obtained, suggested grazing practices for optimum livestock production were developed. Stand density, frequency of occurrence and yield of crested wheatgrass were not affected appreciably during the nine years by light and moderate grazing intensities in the spring. Heavy spring grazing, however, caused a reduction in frequency of occurrence and a lower yield of crested wheatgrass in the latter years of the study. Intensity of grazing in the fall season had little effect on stand density, frequency of occurrence or annual yield of crested wheatgrass. Initial herbage production in the spring was found to be related to the amount of residue remaining after grazing in the previous year. In the heavy spring grazing treatment, each 100 pounds of increased residue produced an average increase of 64 pounds of initial growth. Gains per animal, average daily gains and gains per acre were higher in the spring treatments than in the fall treatments. Average gain per animal and average daily gains were greatest under light and least under heavy grazing in both seasons. Average gains per acre, however, were higher under heavy grazing than light or moderate grazing in both seasons. Plant and animal responses indicate that moderate grazing from early May to late June maintained forage productivity and produced optimum animal response. Forage was wasted with light spring grazing and heavy spring grazing caused a decline in plant vigor, forage productivity and animal response. It was revealed in this study, however, that vigor and production of heavily grazed crested wheatgrass stands could be improved by deferment of grazing for a growing season or two. All intensities of grazing in the fall maintained vigor and production of crested wheatgrass. Gains per animal were slightly less under heavy fall grazing but gains per acre were slightly more than under light or moderate grazing in this season. Information obtained on plant and animal responses indicated that greater livestock production may be realized if the area to be grazed is divided into two or more sections. When this is done, grazing can be alternated between or among the sections in such a way as to allow maximum opportunity for stand maintenance, forage production and animal response. The effectiveness of management programs that developed can be judged by observing the vigor and frequency of occurrence of crested wheatgrass. Dead centers and fragmentation of individual plants of crested wheatgrass occur when grazing is excessive and annual plant species increase in density and frequency. The fragmentation of crested wheatgrass plants into smaller unite made density estimates a less sensitive indication of plant response to grazing than frequency of occurrence. Grazing is abnormally patchy and coarse unpalatable plants are common when the forage is grazed at less than capacity.
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