Biophysical coefficients of evapotranspiration of celery (Apium graveolens) for the Plovdiv area

A three-year field experiment was conducted with celery under irrigated conditions in the Plovdiv region 42° 08‘ 06“ N024° 44‘ 43“ E and 160 m above sea level. The purpose of the development is to establish the biophysical coefficients (Z, R and Ks) of the evapotranspiration of the crop and to recommend the most suitable ones for managing the irrigation regime. The experiment spanned three distinct years, each characterized by varying climatic factors. Throughout all three years, vegetation precipitation was insufficient and unevenly distributed. Post statistical analysis, they were defined as wet, medium and dry. The soil is an alluvial meadow with a bulk density of 1.33 g/cm3 for the 0-0.4m layer where soil moisture was monitored. Real evapotranspiration data of celery, obtained via the weight-thermostat method with regular soil sampling, were used. Three phases of celery development are distinguished, the first being from the interception of seedlings to the beginning of the formation of the root crop, the second - covering the beginning of growth of the root crop and the third phase - from intensive growth to harvest. The Z-factor values by phase were 0.14, 0.21, and 0.24 for R – 0.24, 0.4 and 0.6, and for Kc – 0.65, 1.01 and 1.51.