Evapotranspiration analysis and irrigation requirements of quinoa (Chenopodium quinoa) in the Bolivian highlands

Quinoa (Chenopodium quinoa Willd.) is a staple crop of the Altiplano of the high Andean region, up to 4000 m above sea level, which provides a highly nutritive food for the local and urban population, under adverse climatic conditions of frequent droughts, night frost and poor soils, and is regarded as having a great potential for export. With the aim of increasing production and productivity, new irrigation systems are required. This is causing problems, because the standard FAO formula for calculating reference evapotranspiration ET0 (Penman-Monteith) has not been calibrated for altitudes above 3000 m, so that the crop coefficient K, values for quinoa must be adapted from other crops such as barley and wheat. Additionally, in cases where water availability for quinoa does not reach the levels of crop evapotranspiration ETc the reaction to drought stress and water use efficiency has not been quantified. In order to estimate irrigation requirements of quinoa in a representative site of the Bolivian Altiplano, the crop water requirement, the crop coefficient (K-c), the yield response factor (K-y), and the relative yield, was derived from lysimeter and field data. The Penman-Monteith formula for the conditions of a representative site of the Bolivian Altiplano was calibrated in relation to grass evapotranspiration data, used as reference crop, from lysimeters. The results showed that an excellent agreement exists between measured and calculated ET0 values when an estimate of dew point temperature, derived from minimum air temperature, was used in the calculation instead of recorded humidity data. The Kc for quinoa, obtained from lysimeter data, varied over the growing season being 0.5 in the initial growth stage, 1.00 in the mid-season stage and 0.70 at harvest. The seasonal yield response factor (K-y) of 0.67 was estimated from data on grain yield and crop evapotranspiration obtained in lysimeters. Relative yields obtained from lysimeters, sparsely irrigated and non-irrigated fields, indicate that it may be more profitable to irrigate larger extensions of land using the maximum water use efficiency approach than to irrigate with the same total amount of water to a much smaller area applying maximum water use. (C) 2002 Elsevier Science B.V. All rights reserved.