Effects of different clipping intensities on the forage production in different years (Case study: Saraliabad Gorgan)

This study has been performed in order to determine the effect of clipping intensities of important perennial grasses on the forage production. These experiments have been conducted at the exclosure of Saraliabad Gorgan rangelands. For clipping intensity 25, 50, 75 percent and control (without harvest) have been applied as main factors. In each clipping treatments, 10 individual plant of each species were assessed as replications. Results were analyzed by SAS software in split plot statistical design base on randomize complete design with ten replications at four years (2006 to 2011). The results indicated that there were significant differences between years, intensities of clipping (exception Bromus tomentellus) and their interactions (P<0.01). Generally Agropyron intermedium, Agropyron trichophorum and Poa angustifolia are sensitive to low rainfall and drought, therefore the forage production of these species reduced from 46 to 57% particularly in first year of drought. On the other hand, Festuca ovina showed more resistance and clipping intensities had not significant effect on forage production in dry years. Koeleria cristata and B. tomentellus clipping increased forage production (5 to 33% compare to control treatment) in years with high precipitation and reduced forage production in dry years (4 to 49% compared to control treatment. According to the results of clipping intensities have been determined 60% for F. ovina. In dry years the results showed no grazing for both A. intermedium and A. trichophorum and light grazing (25%) for P. angustifolia but in wet years any limitation of grazing for both A. intermedium and A. trichophorum and light grazing for P. angustifolia have been suggested. No limitation of grazing have been determined for both K. cristata and B. tomentellus in wet years but for dry years clipping intensities estimated 50% and 25% respectively.