CROP EVAPOTRANSPIRATION AND CROP COEFFICIENTS OF VIBURNUM ODORATISSIMUM (KER.-GAWL)

Abstract

Determination of irrigation requirements of nursery plants is becoming more important as the nursery growersare being challenged to conserve water and minimize runoff while meeting plant water needs. Historically, not enoughattention has been given to the measurement of crop evapotranspiration (ETc) and crop coefficients (Kc) of ornamental plantsfor irrigation scheduling, water management, and allocation. Since measurement of Kc is a difficult and time consuming task,especially for the container-grown ornamentals, there is a need to develop methods for estimating Kc from more easilyobtainable variables. The ETc and Kc values of Viburnum odoratissimum (Ker.-gawl) grown in white and black Multi-Pot BoxSystem (MPBS) were measured in two growing seasons (summer and fall). The relationship between the Kc and week aftertransplanting (WAT), growth index (GI), cumulative reference evapotranspiration (ETo), and fraction of thermal units (FTU)were developed and analyzed to find out whether these parameters could be used as the base scales to estimate Kc values.The measured ETc ranged from 308 mm for the black MPBS plants in summer to 351 mm for the white MPBS plants in fall.Good relationships between Kc versus WAT, GI, cumulative ETo, and FTU were observed in both seasons (r2 . 0.93). Theserelationships were explained by third order polynomial equations in both growing seasons. Specifically, GI and FTU valueswere found to be very useful, practical, and effective base scales in estimating Kc from transplanting to physiological maturity(marketable size) of V. odoratissimum. The relationships between the Kc versus base scale variables were significantlyaffected by the season. Thus, the equations developed are season-specific and should be used accordingly. The season-specificcharacteristic of the equations was attributed to the differences in growth rates (exponential in summer and linear in fall)of the plants grown in the white and black MPBS in the summer and fall seasons. Equations developed to estimate Kc wouldhave advantages over the traditional method of estimating Kc from measured ETc and ETo for nursery crops since, in practice,measuring and/or estimating WAT, GI, ETo, and FTU are easier than measuring ETc and Kc. Experimentally derived Kc valuesand relationships developed in this study add useful information to the nursery growers, researchers and water managementdistricts in terms of collection of ETc and Kc data that can be utilized for irrigation scheduling and water resources planningand management, and are among the first ETc and Kc data for the V. odoratissimum.