2017 ASHS Annual Conference

Use of crop coefficients (Kc) in arid climates can provide a valuable tool for optimizing nursery container plant water use. Crop coefficients (Kc) are used to schedule the volumes of irrigation water applied to container plants as a function of previous day container plant water loss to evapotranspiration. The objective of the study was to determine how Kc values change for three edible fruit container-grown nursery plants, Citrus sinensis ‘Arizona Sweet’, Punica granatum ‘Wonderful’, and Ficus carica ‘Black Mission’, during a transitional spring season (February to May 2015) in an arid desert climate of the southwestern United States. Five clones of each taxa were grown in #5 black polyethylene containers (615 cm² container surface area) on top of a black polypropylene plastic fabric ground cover. Containers were oriented in north/south rows at 1-m spacing. Plants were grown outdoors in full sun and hand watered to container capacity every other day during the months of February to May 2015. On data recording days of February 10, March 23, and April 14, all plants were irrigated at 0600HR to container capacity, weighed, and then weighed again after 24 hours. The change in weight was assumed to be evapotranspirational water loss. For Citrus plants, the number of leaves were counted and leaf area were measured with a portable leaf area meter. The Kc of each taxa was calculated using the equations Kc = ETcrop / ET, and ETcrop = water use/container surface area. Estimated water needed (mL) to replace water loss was calculated using (ETcrop x container surface area)/ (1 cm³/mL). For Citrus, estimated water loss (mL) per leaf per square centimeter was calculated by water loss/estimated canopy area. Generally, Citrus had the highest Kc, while Ficus had the lowest. Mean Kc for Citrus ranged from 2.6 to 3.1, for Punica 1.5 to 2.6, and Ficus 1.4 to 1.6. The Kc for Citrus was variable throughout the spring season, while Kc of Punica and Ficus increased as the weather warmed and plants emerged from winter dormancy. The mean measured water loss during the spring months was highest for Citrus, and lowest for Ficus. Based on the changes in Kc values throughout the season, irrigation schedules should be adjusted to account for increased water loss.