Water use and crop coefficients of celery and fennel in Mediterranean environments

A ratio of crop evapotranspiration (ETc) to reference evapotranspiration (ETo) determines a crop coefficient (Kc) value, which is related to vegetation growth and specific crop phenological development. The determination of Kc is important for predicting crop irrigation needs using meteorological data from weather stations. The objective of the research was to determine growth-stage-specific Kc and crop water use for celery and fennel using the experimental data from C.D.S. 'E. Pantanelli' of University Aldo Moro of Bari, located in the countryside of Policoro (MT), southern Italy. Two weighing lysimeters, consisted of undisturbed 4 m2 area of 1.5 m depth of soil monoliths, were utilized to measure crop water use. The lysimeters were located in the center of a 0.5 ha field of square form. Water use was measured on a daily basis. In addition, daily reference evapotranspiration (ETo) was computed by the Penman- Monteith equation, utilizing the weather data collected at the agro-meteorological station near the experimental field. Watering was provided with drip method and scheduled to keep soil water content in the root zone under optimal growing conditions (irrigating at 20% of available water depletion and restoring 100% of the ETc measured daily by lysimeters). The length of crop cycle was 110 and 117 days for celery, and 93 and 135 days for fennel, in the 1st and 2nd year, respectively. For celery, the total ETc amounted to 231.5 and 313.3 mm in the 1st and 2nd year, respectively, and daily Kc ranged between 0.4 and 1.4. For two cultivars of fennel, whose growing cycle took place at different times of the year (August-November 'Conero', and September- February 'Trevi'), the total ETc was equal to 311.7 mm for 'Conero' and 249.8 mm for 'Trevi'. The daily Kc varied between 0.4 and 1.9 for 'Conero' and between 0.5 and 1.7 for 'Trevi'. Specific Kc values across the growing season were determined based on the Kc curves that represent the distribution of Kc over time throughout the season. Hence, it can be highlighted that the values of Kc corresponding to the three typical phenological stages (initial, mid-growth, final) of celery were about 10% higher than those reported in FAO 56 Irrigation and Drainage Paper. The Kc was modelled as a function of days after planting and growing degree days. The later could be more useful for practical applications since reduces the necessity of frequent field observations of phenological phases. The development of regionally based and growth-stage specific Kc curves helps in irrigation management and provides a tool for a better water use in arid and semi-arid areas of the Mediterranean region.