The FAO’s crop model AquaCrop Pasquale STEDUTO Gabriella IZZI & Jippe Hoogeveen Water Unit, Land and Water Division 21/01/2010 FAO, Rome

Background Revision of the 1979 FAO I & D Paper no.33, “Yield Response to Water” (Doorenbos & Kassam)   Consultative process with experts Separation between herbaceous-crops and trees: AquaCrop & Guidelines AquaCrop as one model with crop-specific parameters

{ Evolution from Paper 33 HI E Solar Radiation Biomass=WP · ΣT Canopy AquaCrop (c’) Canopy Transpiration BIOMASS WP HI E daily time-steps Crop Evapotranspiration Paper 33 (c) YIELD Ky long-term sums

AquaCrop Conceptual Framework Atmosphere Crop Management Soil

CLIMATE | Atmosphere AquaCrop Conceptual Framework Rain T (oC) ETo CO2 RS, T, RH, u ETo CO2

| Crop Biomass Phenology Canopy Cover Yield Rooting depth HI AquaCrop Conceptual Framework | Crop CO2 T (oC) ETo Es Ta Biomass WP Phenology Canopy Cover Leaf expansion gs Yield HI Senescence Rooting depth

CC follows the exponential growth during the first half of the full development (Eq. 1) and an exponential decay during the second half of the full development (Eq. 2) (1) (2)

WP Water Productivity (g m-2) (g m-2 mm-1)

Soil water (& salt) balance AquaCrop Conceptual Framework | Soil Rain Irrig. Senescence Leaf expansion gs HI Es Ta Runoff Runoff Ks Soil water (& salt) balance Texture 1 Ksat Infiltration Texture 2 FC Redistribution Uptake Texture … PWP capillary rise deep percolation

+ aeration & T stresses Ks leaf expansion gs senescence HI Ks for leaf expansion, maize (1) leaf expansion Ks for stomata, maize Ks for senescence, maize (2) gs Ks (3) senescence HI (4)

upward or downward adjustment Harvest Index Y HI (biomass) B (yield) adjusted for: water and/or temperature stress Y = HIadj x B multiplier x HIo (reference) upward or downward adjustment

| Management AquaCrop Conceptual Framework Field Management Fertility level (non-limiting; moderate; poor) Field-surface practices (mulching; soil bunds) Water Management Rainfed Irrigation User defined schedule (timing and depth) Model-generated schedule (fixed interval; fixed depth; % of RAW) Irrigation method (drip; sprinkler; surface » basin; border; furrow)

Soil water (& salt) balance Summing up CLIMATE T (oC) Es Ta Phenology Canopy Cover Leaf expansion gs Senescence Biomass WP Yield HI CO2 Soil water (& salt) balance Infiltration Uptake Redistribution deep percolation capillary rise Rooting depth ETo Rain Runoff Atmosphere Soil Crop Management

Conclusions AquaCrop is explicit and mostly intuitive, and maintains an optimum balance between simplicity, accuracy and robustness AquaCrop differs from other models for being water-driven, using CC instead of LAI, not having partitioning except than HI, not attempting nutrient balance but relate to fertility regimes, and for its relatively lower number of parameters AquaCrop is aimed at practical end-users, as those in farmers and irrigation associations, extension services, governmental agencies and NGOs, planners and economists, for devising water management and saving strategies, and productivity analysis as well AquaCrop is also particularly suited for perspective studies (e.g., under different climate change scenarios)

Main scientific publications

Crops dealt by AquaCrop About to be released (January 2010) Already calibrated For the future Wheat Maize Rice Sugarbeet Soybean Cotton Potato Quinoa Sunflower Sugarcane Tomato Teff Bambara Groundnut Forage crops (Alfalfa) Millet Barley Chickpea Sorghum NO TREE CROPS

Thank You www.fao.org/nr/water