New version of FAOs' crop-water productivity model AquaCrop now available

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AquaCrop is a crop-water productivity model developed by FAO’s Land and Water Division to address food security and assess the effect of the environment and management on crop production. AquaCrop simulates the yield response of herbaceous crops to water and is particularly well suited to conditions in which water is a key limiting factor in crop production. AquaCrop balances accuracy, simplicity and robustness. To ensure its wide applicability, it uses only a small number of explicit parameters and mostly intuitive input variables that can be determined using simple methods.

To be widely applicable AquaCrop uses only a relatively small number of explicit parameters and mostly-intuitive input-variables requiring simple methods for their determination. On the other hand, the calculation procedures is grounded on basic and often complex biophysical processes to guarantee an accurate simulation of the response of the crop in the plant-soil system.

Practical applications

AquaCrop can be used as a planning tool and to assist management decisions in both irrigated and rainfed agriculture. AquaCrop is particularly useful for:

  • understanding crop responses to environmental change (i.e. as an educational tool)
  • comparing attainable and actual yields in fields, farms and regions
  • identifying constraints to crop production and water productivity (e.g. as a benchmarking tool)
  • developing irrigation schedules for maximum production (e.g. seasonal strategies and operational decision-making, and for climate scenarios)
  • developing strategies under water-deficit conditions to maximize water productivity through:
    • irrigation strategies (e.g. deficit irrigation)
    • crop and management practices (e.g. adjusting planting dates, cultivar selection, fertilization management, the use of mulches, and rainwater harvesting)
  • studying the effect of climate change on food production (for example by running AquaCrop with both historical and future weather conditions)
  • analysing scenarios useful for water administrators and managers, economists, policy analysts and scientists (i.e. planning purposes)
  • supporting decision-making on water allocations and other water policies.

Limitations

The limitations of AquaCrop are as follows:

  • AquaCrop can simulate daily biomass production and final crop yields for herbaceous crops with single growth cycles only.
  • AquaCrop is designed to predict crop yields at the single field scale (point simulations). The field is assumed to be uniform without spatial differences in crop development, transpiration, soil characteristics or management.
  • Only vertical incoming (rainfall, irrigation and capillary rise) and outgoing (evaporation, transpiration and deep percolation) water fluxes are considered.

Target audience

AquaCrop is intended mainly for practitioners working for extension services, governmental agencies, non-governmental organizations or farmer associations. It will also be useful to scientists and as a training and education tool on the role of water in determining crop productivity.

Calculation scheme

AquaCrop simulates final crop yield in four steps (which run in series in each daily time increment), as described below. The four steps are easy to understand, thereby ensuring transparency in the modelling approach.

  1. Development of green canopy cover: in AquaCrop, foliage development is expressed through green canopy cover (CC) rather than leaf area index. CC is the fraction of the soil surface covered by the canopy; it ranges from zero at sowing (i.e. 0 percent of the soil surface covered by the canopy) to a maximum value at mid-season as high as 1 if full canopy cover is reached (i.e. 100 percent of the soil surface is covered by the canopy). By adjusting the water content in the soil profile each day, AquaCrop keeps track of stresses that might develop in the root zone. Soil-water stress can affect the leaf and therefore canopy expansion; if severe it can trigger early canopy senescence.
  2. Crop transpiration: in well-watered conditions, crop transpiration (Tr) is calculated by multiplying the reference evapotranspiration (ETo) with a crop coefficient (KcTr). The crop coefficient is proportional to CC and hence varies throughout the life cycle of a crop in accordance with the simulated canopy cover. Not only can water stress affect canopy development, it can also induce stomata closure and thereby directly affect crop transpiration.
  3. Above-ground biomass: the quantity of above-ground biomass (B) produced is proportional to the cumulative amount of crop transpiration (ΣTr); the proportional factor is known as biomass water productivity (WP). In AquaCrop, WP is normalized for the effect of climatic conditions, making normalized biomass water productivity (WP*) valid for diverse locations, seasons and concentrations of carbon dioxide.
  4. Crop yield: the simulated above-ground biomass integrates all photosynthetic products assimilated by a crop during the season. Crop yield (Y) is obtained from B by using a harvest index (HI) – which is the fraction of B that is harvestable product. The actual HI is obtained during simulation by adjusting the reference harvest index (HIo) with an adjustment factor for stress effects.

Read more about the AquaCrop calculation scheme...

Input requirement

AquaCrop uses a relative small number of explicit parameters and largely intuitive input variables that are either widely available or can be determined using simple methods. Inputs consist of weather data, crop and soil characteristics, and management practices that define the environment in which the crop will develop. Soil characteristics are divided into soil profile and groundwater characteristics, and management practices are categorized as field management or irrigation management practices (see figure).

Read more about the required input for simulations with AquaCrop...

AquaCrop Core Group