Additional research products (ARP2): VADAS models (Vulnerability Assessment to Desertification of Agricultural Systems)

Authors:

Vadas herbaceous: Alfonso Domínguez and José Mª Tarjuelo (UCLM)
Vadas tree crops: Elias Fereres ag1fecae@uco.es and Lola Suarez
(IAS-CSIC)

VADAS (Vulnerability Assessment to Desertification of Agricultural Systems) is a spatially distributed farm model forecasting both crop growth and the economic value of the crop over an area.

It can be used as a support tool for evaluating the impact of desertification on the agricultural land use systems. TheVADAS model generates a forecast of four output variables over the area of interest:

Biomass production.
Relationship between water used by the crop (rainfall and irrigation for herbaceous crops and irrigation for rain-fed trees) and the gross margin obtained.
Daily progression of Biomass and Leaf Area Index (LAI).
Spatial crop distribution that maximizes the gross margin for an agricultural system or a farm.

VADAS modules have been created using existing models as building blocks.

The VADAS module for herbaceous crops is based on MOPECO and CROPSYST and the tree orchards module is based on Wofost. The modifications from the original models are explained in the technical description below.

The VADAS model for herbaceous crops comprises two computing modules:

Module I determines seasonal net irrigation depths under stress (due to lack of water and/or soil salinity) and non-stress conditions. In addition, this module employs a normal statistical distribution to simulate water distribution for the irrigation system based on the Christiansen's Uniformity Coefficient (CU). By considering the crop yield and economic data, the gross margin is related to the irrigation depth for each crop.

Module II identifies cropping patterns and irrigation strategies that maximize total profits on a farm. This optimum takes account of restrictions imposed by the process (available water, area, etc.).

The tree orchard module is parallel to Module I for herbaceous crops. It is based on Wofost model but new routines for water balance and crop growth have been added.

This model has been validated for the Eastern La Mancha agricultural system and for Andalusia (Spain). In addition, a list of indicators related with desertification in agricultural systems has been developed.
The necessary inputs are: Weather (values for solar radiation, maximum and minimum temperatures, precipitation, vapour pressure and wind speed), Crop inputs (Canopy volume per unit area, Leaf Area Density, Planting density, Harvest Index, Radiation Use Efficiency, Crop Evapotranspiration Coefficient), Soil characteristics (soil moisture content [cm3/cm3] at field capacity, wilting point and saturation, Maximum rooting depth, Total evaporation during the energy-limiting stage, Alfa soil parameter for the evaporation falling rate stage, Maximum percolation rate root zone, Initial soil moisture in the surface layer and in the root zone).

The model estimates crop yield, production and gross margin as a function of the irrigation depth. Finally, these gross margin functions are used to determine an optimum cropping pattern and irrigation strategy to maximize the gross margin on a farm in a specific scenario.

The last version of the model and the user's manual can be downloaded at http://crea.uclm.es/crea2/en/descarga.php