Introducing deficit irrigation to stabilize yields of quinoa (Chenopodium quinoa Willd.)
Agriculture needs to increase its production with a small amount of available fresh water. Deficit irrigation (DI) is now widely been investigated as one of the solutions for this problem. The effects of concentrated drought stress in various phenological stages of quinoa on total production were assessed in above-ground mini-lysimeters under controlled conditions in the Bolivian Altiplano. From the results of the controlled experiment a promising DI strategy was obtained which consisted in mitigating droughts during plant establishment and during the reproductive stage (flowering and early grain filling). The DI strategy was tested in the field by respecting local agricultural practices and compared with full irrigation (FI) and rainfed treatments. The field experiments were conducted in two locations in the central Bolivian Altiplano (Patacamaya and Condoriri) and in two cropping seasons (2005–2006, and 2006–2007). The performance of quinoa in all experiments was assessed by measuring total seed yield, seed size, harvest index (HI) and water use efficiency (WUE). From the controlled experiment, the negative effect of continuous drought was demonstrated. The milky grain phase was observed as being most sensitive to drought stress, followed by the flowering stage. Drought stress after emergence till the 6-leaf stage and from the 6-leaf stage till the 12-leaf stage did not cause lower yields and resulted in equal or higher WUE than FI. In Condoriri no significant differences were found between the DI and rainfed treatment as a result of the good rainfall distribution during the critical phenological stages. The DI strategy in Patacamaya in 2005–2006 resulted in significantly higher yields (2 Mg/ha) and 1000 seed mass (5.5 g) as compared to the rainfed treatment (1.7 Mg/ha and 4.2 g, respectively). The field experiment of 2006–2007 indicated that additional irrigation during the late vegetative stage is redundant and that a DI strategy with irrigation only during plant establishment is insufficient. A significant, negative linear relation was demonstrated in the mini-lysimeter and field experiments between pre- and post-anthesis ETa and WUE, indicating the extra harmful character of droughts during flowering and grain filling if the crop did not suffer drought stress before flowering. From the field results, former studies and observations in farmers’ fields, indicative values for the net irrigation requirement, expected yields and WUE for various management conditions, irrigation applications and for different types of years were derived. It is believed that quinoa yields can be stabilized at 1.2 up to 2 Mg/ha with the help of DI by applying only half of the irrigation water required for full irrigation.