Determination of Crop Coefficient and Water Requirement for Quinoa by Lysimetric Method in Birjand Plain

Estimating potential evapotranspiration values is very important for calculating the water requirement in line with agricultural planning for different crops. For this purpose, in the present study, three polyethylene lysimeters with drains and completely sealed, with a diameter of 60 cm and a height of 100 cm were used to determine the crop coefficient and water requirement of quinoa. Titicaca quinoa seeds were planted on May 7, 2019, with 60 plants/m2. The soil moisture level was recorded by TDR and also the drainage output in each lysimeter was measured before irrigation. In order to measure potential evapotranspiration, the equations of Penman-Monteith, Blaney-Criddle (based on temperature) and Priestley-Taylor (based on radiation) were used. The results showed that the total amount of potential evapotranspiration during the growing season according to the FAO Penman-Monteith (ETo) method was 720 mm, according to the Blaney-Criddle method 581 mm, and according to the Priestley-Taylor method, 754 mm, while the total evapotranspiration of quinoa (ETc) in lysimeters was 553 mm. Also, the value of quinoa crop coefficient (Kc) in the first stage (21 days period), second stage (26 days period), third stage (38 days period) and fourth stage of quinoa growth (34 days period) using the Penman-Monteith method was equal to 0.42, 0.66, 1.03 and 0.71, in Blaney-Criddle method, 0.54, 0.88, 1.28 and 0.82, and in Priestley-Taylor method 0.40, 0.62, 0.97 and 0.68, respectively. These results show the Penman-Monteith method, as the best method, can be used as a criterion for determining the potential evapotranspiration, but the Blaney-Criddle method needs to be calibrated in the region.