Crop coefficient of sesame in a semi-arid region of I.R. Iran

Crop coefficient of sesame is necessary for the water requirement estimation in irrigation water planning and management. This study has been initiated to determine the crop coefficient (Kc) of sesame in a semi-arid climate. The relationships between Kc and ETp/Ep (pan evaporation) and leaf area index (LAI), growing degree-day (GDD) and days after sowing (DAS), were also investigated. The seasonal ETp for sesame in the study area with a 5 month growth period was 910 m. The mid-season and late-season Kc values for sesame were 1.08 and 0.64, respectively. These values are somewhat lower and higher than those for other oil seed crops. The Kc value for the initial stage was close to that obtained by the procedure proposed by Allen et al. [Allen, R.G., Smith, M., Pereira, L.S., Pruitt, W.O., 1997. Proposed revision to the FAO procedure for estimating evapotranspiration. In: The Second Iranian Congress on Soil and Water Issues, 15–17 February 1997. Tehran, I.R. of Iran, pp. 1–18]. The ratio of ETp/Ep varied between 0.49–1.0 from the beginning to the middle of the growing season which is a sign of mild local advection in the region. The maximum ratios of ETp/ET0 and ETp/Ep occurred at a LAI of 3.0. Furthermore, third-order polynomials were presented to predict the Kc values from days after sowing (DAS), percent days after sowing (%DAS) and growing degree-day (GDD).