Document Type : Research Paper
Authors
1 Ph.D. Graduate Student of Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran, and Research Instructor of Agriculture and Natural Resources Research Center of Kurdistan,
2 Professor of Department of Rangeland Science, Faculty of Rangeland and Watershed Management, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
3 Professor of School of Plant Sciences, College of Agriculture and Life Sciences, The University of Arizona, Tucson, AZ 85721, USA
4 Assistant Professor of Department of Rangeland and Watershed Management, Islamic Azad University – Arsanjan Branch, Arsanjan, Iran
5 Associate Professor of Department of Agronomy, University of Kurdistan, Sanandaj, Iran.
Abstract
This study conducted to investigate the effects of grazing in a short-term stocking system on the water-soluble carbohydrates (WSC) and nitrogen (N) reserves of permanent parts of Bromus tomentellus, Cephalaria kotschyi and Ferula haussknekhtii in Saral rangelands. A key area was selected with a permanent exclosure area and two temporary exclosure areas. Root excavation was conducted at six to nine phenological stages. Five samples of typical plants were randomly selected for each species at each stage at each of these two sites for studying. Before excavation of the plants, their heights, canopy cover and basal area were measured. WSC and N concentrations were determined as a percentage of sample dry matter with phenol-sulphuric acid and Kjeldahl methods, respectively. The WSC concentration of B. tomentellus was not affected neither by studied grazing conditions nor by differences of weather conditions of the studied years. This species had lower carbohydrate concentrations than the forbs. In C. kotschyiWSC level was not affected by grazing or the weather condition each year. The low point of WSC reserves in F. haussknekhtii occurred during the rapid spring growth, and the highest levels were attained at the end of its growing seasons. Grazing increased the WSC concentrations in the storage organs of the plants of F. haussknekhtii and N concentrations of all the studied species. This study suggested that the plant response to grazing increased the resource allocation to storage organs to compensate the deprived reserves in the studied grazing system, so that the rest periods works well to improve the plants’ vigor. It seems that livestock grazing in this grazing system does not significantly harm two of the three studied species in their sizes.
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