Modelling evapotranspiration of seed propagated globe artichoke in a Mediterranean environment.

This work aims at improving the estimation of artichoke evapotranspiration in Mediterranean climates through the modelling of crop coefficients (Kc) and duration of phenological phases of a seed propagated artichoke. A two years trial was carried out at the experimental station "E. Pantanelli" of University Aldo Moro (Bari), located in the countryside of Policoro (MT), southern Italy. The seed propagated artichoke cv. 044 was grown in two weighing lysimeters placed in a large field and watered regularly. The irrigation was applied when 40% of total available water in the soil layer occupied by roots was consumed which corresponded to the crop evapotranspiration (ETc) between 25 and 40 mm. Irrigation was applied in such a way to replenished completely the depletion of water in the root zone. The reference evapotranspiration (ETo) was computed daily, by using Penman-Monteith equation from the weather data collected at the agro-meteorological station near the experimental field. The growing season started in mid of July and ended in the second part of May. The artichoke crop cycle was 310 and 313 days in the 1st and 2nd year, respectively. Average seasonal ETc measured at two lysimeters was slightly higher in the 1st year (967 mm) than in the 2nd one (911 mm). Water use obtained in this trial was 85% higher than usually reported in the literature for vegetatively propagated crops in the same area and with similar crop length. Most likely this was due to taller crops (1.7 in respect to 0.8 m) and higher biomass production in seed propagated crop. Crop coefficients (Kc), calculated daily as the ratio between ETc and ETo, revealed that five phenological stages could be considered in ETc estimate: i) the seedling establishment of about 30 days; ii) the initial development phase of approximately 60 days; iii) winter vegetative stagnation of approximately 90 days; iv) spring recovery of about 90 days, and v) full development stage of about 45 days. The Kc values during the seedling establishment were between 0.3 and 0.4 and increased up to 0.8-0.9 at the end of initial development period. The Kc values were reduced gradually to 0.4 at the end of winter vegetative stagnation and then increased up to 1.1 during the full development period. The presented results differ from those available in the literature since they refer to a seed propagated artichoke which is taller and more vigorous than vegetatively propagated crop. In the last years, the former crop tends to substitute the later one in many Mediterranean areas and a proper crop evapotranspiration estimate and irrigation management are of crucial importance for a more efficient water use in the region. Further efforts could focus on the introduction of the growing degree days concept and substitution of sum of days with thermal sums as well as on the link between Kc and leaf area index (LAI).