عنوان مقاله [English]
This study was conducted to evaluate the effects of different levels of irrigation water and potassium fertilizer on the yield and its components of sorghum forage. This research was carried out in the Agricultural Research Center of Semnan (Shahrood) in 2014. The factors in this study were the irrigation water in three levels (50, 75 and 100% water requirement) and potassium fertilizers in three levels (0, 50 and 100% of the required fertilizer based on soil test) and forage sorghum varieties (Pegah, Karaj and Speed feed). The analysis of variance of data showed that the factors of water and potassium fertilizer on yield, shoot dry weight, plant height, number of leaves per plant, leaf dry weight, leaf area and stem dry weight were significant (1%). The highest forage yield was obtained from the 100 percentage level of the water and fertilizer. The efficiency of water use in water level of 75 percent was more than other levels. The highest yield was observed from W100K100 treatment. Thus W75K100Vp treatment was recommended as a superior treatment. To determine the functions of forage yield - water - potassium fertilizer, linear, logarithmic linear, quadratic and exponential mathematical equations were used. The Quadratic equation was chosen as the premier equation. In order to study the separate and combined effects of irrigation water and potassium fertilizer on the yield forage sorghum, the marginal production (MP) and the rate of substitution (MRTS) for irrigation water and potassium fertilizers were calculated. The marginal production of water irrigation (MPI) and marginal production of potash fertilizers (MPK) were equal to 1.52 tons per cm and 0.076 (ton/ kg. ha), respectively. The rate of technical substitution of potassium fertilizer instead of irrigation water (MRTS) for forage yield was determined as 0.05 kg. The average monetary value of forage and final production of potassium fertilizers were obtained as 3040000 and 152000 rials respectively.