crop coefficient of the medicinal plant Evening Primrose (Oenohera biennis L.)

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In all methods in which the evapotranspiration of plants is counted as a reference, in order to generalize the results to the vegetation, it is necessary to multiply the acquired amount to the crop coefficient. An experiment was done to estimate the crop coefficient amount of evening primrose that was repeated four times in a time period of 70 days on March 2018.[D1], in a weather station located in the agriculture college of Ferdowsi University of Mashhad. In this experiment, the plants were cultivated in white plastic pots (micro-lysimeter) by 50 centimetre height and 30 centimeter width. The demanded amount of water to provide the plants' water needs is considered based on the field capacity. By controlling the water balance in pots, the evapotranspiration of plants was measure and by the use of evaporation pan A data, the crop coefficient was calculated. According to the results of this study the crop coefficient of evening primrose in the initial, middle and final steps are 0.75, 1.05 and 1.00 respectfully. The average in whole the period evening primrose growth was 0.92. The total amount of evapotranspiration of plants was estimated to be about 377 millimeters.