The FAOs crop model Aqua Crop Pasquale STEDUTO

The FAO’s crop model Aqua. Crop Pasquale STEDUTO Gabriella IZZI & Jippe Hoogeveen Water Unit, Land 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: Aqua. Crop & Guidelines • Aqua. Crop as one model with crop-specific parameters

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

Aqua. Crop Conceptual Framework Crop Soil Management Atmosphere

Aqua. Crop Conceptual Framework | Atmosphere CLIMATE Rain T (o. C) RS, T, RH, u ETo CO 2

Aqua. Crop Conceptual Framework | Crop CO 2 T (o. C) Phenology ETo Es Leaf expansion Ta gs Canopy Cover Senescence Rooting depth WP Biomass HI Yield

• 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)

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

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

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

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

Aqua. Crop Conceptual Framework | Management 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)

Summing up CLIMATE Atmosphere Rain ETo T (o. C) Crop Soil Phenology Management Runoff Es Leaf expansion CO 2 Ta gs Canopy Cover Senescence WP Biomass Rooting depth Infiltration Soil water (& salt) balance Uptake Redistribution capillary rise deep percolation HI Yield

Conclusions • Aqua. Crop is explicit and mostly intuitive, and maintains an optimum balance between simplicity, accuracy and robustness • Aqua. Crop 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 • Aqua. Crop 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 • Aqua. Crop is also particularly suited for perspective studies (e. g. , under different climate change scenarios)

• Main scientific publications

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

Thank You www. fao. org/nr/water