AquaCrop

AquaCrop is a crop water productivity model developed by the Land and Water Division of FAO.

It simulates yield response to water of herbaceous crops, and is particularly suited to address conditions where water is a key limiting factor in crop production.

AquaCrop attempts to balance accuracy, simplicity, and robustness. It uses a relatively small number of explicit and mostly-intuitive parameters and input variables requiring simple methods for their determination.

Applications of AquaCrop include:

  • assessing water-limited, attainable crop yields at a given geographical location
  • as a benchmarking tool, comparing the attainable yields against actual yields of a field, farm, or region, to identify the yield gap and the constraints limiting crop production
  • assessing rainfed crop production on the long term
  • developing irrigation schedules for maximum production (seasonal strategies and operational decision-making), and for different climate scenarios
  • scheduling deficit and supplemental irrigation
  • evaluating the impact of fixed delivery irrigation schedules on attainable yields
  • simulating crop sequences
  • carrying out future climate scenario analyses
  • optimizing a limited amount of water available (economic, equitability, and sustainability criteria)
  • evaluating the impact of low fertility and of water-fertility interactions on yields
  • assessing actual water productivity (biological and/or economic) at the field and higher scales, up to regions
  • supporting decision making on water allocation and other water policy actions
  • appraising the role of various water-related crop responses in yield determination for ideotype design

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AquaCrop is mainly intended for practitioners such as those working for extension services, governmental agencies, NGOs, and various kinds of farmers associations. It is also of interest to scientists and for teaching purposes, as a training and education tool related to the role of water in determining crop productivity.

AquaCrop results from the revision of the FAO Irrigation and Drainage Paper No. 33 “Yield Response to Water” (Doorenbos and Kassam, 1979), a key reference for estimating the yield response to water. AquaCrop evolves from the fundamental equation of Paper No. 33, where relative yield (Y) loss is proportional to relative evapotranspiration (ET) decline, with Ky as the yield response proportional factor.
AquaCrop advances from the Ky approach by:
(i) dividing ET in soil evaporation (E) and crop transpiration (Tr), to avoid the confounding effect of the non-productive consumptive use of water (E),
(ii) obtaining biomass (B) from the product of water productivity (WP) and cumulated crop transpiration,
(iii) expressing the final yield (Y) as the product of B and Harvest Index (HI),
(iv) normalizing Tr with reference evapotranspiration (ETo), to make the B-Tr relationship applicable to different climatic regimes, and
(v) running with daily time steps (either calendar or growing degree days), to more realistically account for the dynamic nature of water stress effects and crop responses.
As the Ky approach, AquaCrop is water-driven, meaning that the crop growth and production are driven by the amount of water transpired (Tr). AquaCrop focuses on the fundamental relation between B and Tr rather than Y and ET (as in the Ky approach), relying on the conservative behaviour of WP. A schematic representation of these evolutionary steps is reported in the figure below.

AquaCrop includes the following sub-model components: the soil, with its water balance; the crop, with its development, growth and yield; the atmosphere, with its thermal regime, rainfall, evaporative demand and CO2 concentration; and the management, with its major agronomic practice such as irrigation and fertilization. AquaCrop flowchart is shown below.

Download AquaCrop from fao here

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