Using the FAO dual crop coefficient approach to model water use and productivity of processing pea (Pisum sativum L.) as influenced by irrigation strategies

Aiming at improved knowledge on water use, productivity and irrigation scheduling of processing pea, the soil water balance model SIMDualKc was calibrated and validated using field data observed in two farmers' fields in a wet and a dry year. The model uses the dual crop coefficient approach for partitioning crop evapotranspiration into crop transpiration and soil evaporation. Calibration was performed by minimizing differences between measured and simulated soil water content with a root mean square error representing 2% of the measured mean. The calibrated basal crop coefficients for the initial, mid-season and end-season were respectively 0.15, 1.15 and 1.10. Pea commercial yield (5084-8197 kg ha−1), obtained from the total yield using industry textural and quality criteria, was influenced by climatic conditions and the harvesting date. Using the global water-yield function with Ky = 1.15 and the actual crop transpiration computed with SIMDualKc, the fresh and commercial yields were estimated with errors smaller than 3.5%. Water productivity relative to the commercial yield varied 1.51-2.67 kg m−3, mainly depending on the yield achieved rather than on water use. Results from the economic water productivity ratio (EWPR), which compares the commercial yield value with the corresponding production costs, varied 1.07-1.82. Because irrigation costs were a small fraction of the total costs, EWPR values mainly varied with the commercial yield and less with irrigation costs. Irrigation scheduling alternatives for wet and dry years showed that water saving is achievable without considerably affecting peas' yield and economic results. Results show that the SIMDualKc model is appropriate to support irrigation advising.