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SYMPOSIUM PAPERS

Simulating Yield Response of Quinoa to Water Availability with AquaCrop

^a Faculty of Bioscience Engineering, Division of Soil and Water Management,K.U. Leuven Univ., Celestijnenlaan 200E, PostBox 02411, B-3001, Leuven, Belgium
^b Faculty of Agronomy, Univ. Mayor de San Andres (UMSA), Héroes del Acre No. 1850, La Paz, Bolivia
^c Faculty of Agronomy, Univ. Tecnica de Oruro (UTO), Av. 6 de Octubre, Oruro, Bolivia
^d Water Resources, Development and Management Service, Land and Water Division, FAO, Room B-721, Via delle Terme di Caracalla 00135, Rome, Italy

^* Corresponding author (sam.geerts{at}biw.kuleuven.be).

The modeling of yield response to water is expected to play an increasingly important role in the optimization of crop water productivity (WP) in agriculture. During 3 yr (2004–2007), field experiments were conducted to assess the crop response to water stress of quinoa (Chenopodium quinoa Willd.) in the Bolivian Altiplano (4000 masl) under different watering conditions (from rain fed, RF, to full irrigation, FI). Crop physiological measurements and comparisons between simulated and observed soil water content (SWC), canopy cover (CC), biomass production, and final seed yield of a selected number of fields were used to calibrate the AquaCrop model. Subsequently, the model was validated for different locations and varieties using data from other experimental fields and from farmers' fields. Additionally, a sensitivity analysis was performed for key input variables of the parameterized model. AquaCrop simulated well the decrease of the harvest index (HI) of quinoa in response to drought during early grain filling as observed in the field. Further-on, the procedure for triggering early canopy senescence was deactivated in the model as observed in the field. Biomass WP (g m^–2) decreased by 9% under fully irrigated conditions compared with RF and deficit irrigation (DI) conditions, most probably due to severe nutrient depletion. Satisfactory results were obtained for the simulation of total biomass and seed yield [validation regression R² = 0.87 and 0.83, and Nash-Sutcliff efficiency (EF) = 0.82 and 0.79, respectively]. Sensitivity analysis demonstrated the robustness of the AquaCrop model for simulation of quinoa growth and production, although further improvements of the model for soil nutrient depletion, pests, diseases, and frost are also possible.

Abbreviations: B, total oven-dry aboveground biomass • CC, canopy cover • CC_o, initial canopy cover • CC_x, maximum canopy cover • DI, deficit irrigation • EF, Nash-Sutcliff efficiency • ET_c, crop evapotranspiration • ET_o, reference evapotranspiration • FC, field capacity • FI, full irrigation • GDD, growing degree days • HI, harvest index • K_sat, saturated hydraulic conductivity • LAI, leaf area index • p, water stress factor • PWP, permanent wilting point • RF, rain fed • RRMSE, relative root mean squared error • SWC, soil water content • Tr_a, actual transpiration • TAW, totally available water in the soil between field capacity and permanent wilting point • WP, water productivity • WP*, water productivity, normalized for ET_o • Y, total seed yield • Z_x, maximum rooting depth

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Received for publication April 29, 2008.

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