Improving product quality and timing of Kalanchoe: Model development and validation

Predicting and controlling the visual product quality and the cropping duration is of utmost importance in year-round flowering pot plant production. Explanatory crop growth and quality models are valuable tools for scenario studies and dynamic crop control. A dynamic model was developed, calibrated and validated for plant height and cropping duration of Kalanchoe blossfeldiana. Data from a previously published study conducted in climate chambers with cultivar 'Anatole', under all combinations of four constant temperatures (18, 21, 23 and 26 degrees C, equal day and night) with four photosynthetic photon flux densities (PPFD, 60, 90, 140 and 200 mu mol m(-2) s(-1)), were used for model development and parameter estimation (calibration). Plant height was modelled taking into account the vegetative internode appearance rate (optimum response to both temperature and light) and the individual vegetative internode length against time, described by a Richards function. The asymptotic maximum (A) in this function increased linearly with light and quadratically with temperature. Added to this vegetative length is the generative length. The starting date of generative elongation quadratically decreased with temperature and light and generative elongation rate showed a linear increase with temperature and light. Cropping duration was predicted using the rate of flower development (inverse of reaction time, i.e. the time from start of short day until harvest stage), which increased quadratically with temperature and with light (no interaction). These modules were validated, with an independent data set collected at a commercial greenhouse in two growth seasons (winter and summer). Cropping duration was predicted well, but plant height was underestimated. The achievements and limitations of modelling dynamically the plant height and the cropping duration in year-round kalanchoe production are discussed.