Could deficit irrigation be a sustainable practice for quinoa (Chenopodium quinoa Willd.) in the Southern Bolivian Altiplano?

The application of deficit irrigation (DI) to stabilize yield and to increase water productivity of quinoa (Chenopodium quinoa Willd.) raises questions in the arid Southern Altiplano of Bolivia where water resources are limited and often saline. Rainfed quinoa and quinoa with irrigation restricted to the flowering and early grain filling were studied during the growing seasons of 2005-2006 and 2006-2007 in a location with (Irpani) and without (Mejillones) water contribution from a shallow water table. It was found that the effect of additional irrigation was only significant above a basic fulfillment of crop water requirements of around 55%. Below this threshold, yields, total water use efficiency (TWUE) and marginal irrigation water use efficiency (MIWUE) of quinoa with DI were low. Capillary rise (CR) from groundwater was assessed using the one-dimensional UPFLOW model. The contribution of water from capillary rise in the region of Irpani ranges from 8 to 25% of seasonal crop evapotranspiration (ETc) of quinoa, depending mostly on the depth of the groundwater table and the amount of rainfall during the rainy season. DI with poor quality water and cultivation of crops in fields with a shallow saline groundwater table pose a serious threat for sustainable quinoa farming. To assess the impact of saline water resources, soil salinity and required leaching were simulated by combining the soil water and salt balance model BUDGET with UPFLOW. The results indicate that irrigation of quinoa with saline water and/or CR from a saline shallow water table might, already after 1 year, result in significant salt accumulation in the root zone in the arid Southern Altiplano. A farming system with only 1 year fallow is often insufficient to leach sufficient salts out of the root zone. In case the number of fallow years cannot be increased, leaching by means of an important irrigation application before sowing is an alternative. Although potentially beneficial, DI of quinoa in arid regions such as the Southern Bolivian Altiplano should be considered with precaution.