Improving irrigation practices in container stock plant production of herbaceous plant cuttings

The majority of stock plants for producing cuttings of herbaceous ornamental plants for export to the US and Europe are located in Africa and Latin America. Plants are typically produced in bags or plastic containers, often with a locally-available volcanic rock or pumice substrate, and irrigation with a nutrient solution provided through drip emitters. Nutrient solution in many farms is not captured for treatment and recirculation in order to avoid the risk of disease transmission, and leaching fractions can be as high as 80%. The objective was to evaluate alternative approaches to measure water and nutrient use efficiency, and reduce leaching of nutrient solution. Dielectric soil moisture sensors (SMS) at the University of Florida (UF) were tested in both a 90% perlite/10% coconut coir substrate and a volcanic rock substrate over two years. The SMS were calibrated to monitor and automatically control moisture level in geranium (Pelargonium × hybrida) plants. Leaching fraction was 20 to 25% in the coir substrate, however, leaching rate increased when the highly porous volcanic substrate was used. An evapotranspiration model for geranium was also calibrated using vapor pressure deficit, light, and leaf area. Data on leaf area, climate, water, and nutrient use were collected from commercial geranium stock farms in East Africa. Leaching fraction (drained irrigation volume/applied irrigation volume) averaged 65 and 40% (397 or 111 mL container^-1 day^-1) at the commercial locations, indicating high potential to improve irrigation efficiency. In commercial stock farm locations, we concluded that climate monitoring and moisture sensors were useful tools, but that other aspects including the substrate physical properties, irrigation uniformity and infrastructure, and staff training were also important to improve watering decisions.