Distributed FAO56 Agro-Hydrological model for irrigation scheduling in olives orchards

Accurate estimations of crop water requirements are necessary to improve water use in agriculture and to optimize the use of available freshwater resources. To this aim, Agro-Hydrological models allow to quantify crop water requirements which depend on actual crop evapotranspiration (ETa). The use of remotely sensed data is a way to accurately estimate time series of ETa 2D maps. Indeed, the use of remote observations represents a reliable strategy to identify the spatial distribution of vegetation biophysical parameters, such as crop coefficients (Kc and/or Kcb) under actual field conditions. The objective of this research was to assess the crop water requirements and irrigation scheduling inside an irrigation district, located near to Castelvetrano, Sicily (Italy), characterized mainly by olives orchards, using the FAO56 Agro-Hydrological model joint with a functional relationship between basal crop coefficient (K-cb), and the Normalized Difference Vegetation Index (NDVI) obtained from Sentinel-2 Multispectral Images (MSI) - level 2A. FAO56 Agro-Hydrological model was applied for the 2018 irrigation season. The model was implemented in two different modes to estimate spatial and temporal variability of the ETa, soil water content (SWC) in the root zone, as well as the irrigation scheduling. In the Castelvetrano irrigation district 1/A, a linear K-cb(NDVI) relationship was identified following the Allen and Pereira (A&P) procedure which is based on the knowledge of the canopy characteristics, meteorological variables, and the fraction of vegetation cover (f(c)); the latter estimated via the NDVI. The difference between irrigation volumes provided by the farmer and estimated by the model was equal to 3%. This encouraging result highlights that the proposed model can be a useful tool for supporting the decision in the irrigation demands management in the district.