A CONCEPTUAL DYNAMIC MODEL FOR EXTERNAL QUALITY IN KALANCHOE

Abstract

Modelling quality in pot plants is still a weak feature in crop modelling research. This work aims at building a conceptual dynamic model for external quality (plant height and number of flower heads) in Kalanchoe blossfeldiana. Four experiments were conducted to quantify the effects of temperature and spacing schedules at two different planting dates. Five constant temperatures (18, 20, 22, 24 and 26°C) and nine spacing schedules, resulting from combinations of spacing at a given leaf area index (LAI: 1.6, 2, 3, 4 and 4.4) into a final plant density (31.1, 34.6, 43.4, 52.0 and 55.6 plants m-2) were studied. Stem length was modelled as the number of internodes (same as number of leaf pairs) times the average internode length. Plant height results from the stem length plus the uppermost pedicel length. The spacing schedules did not affect plant height, but total aerial dry mass (TDM, g plant-1), leaf area and number of flower heads were increased at earlier and wider spacing. In contrast, temperature had a significant effect on the average internode length (internode elongation rate linearly increased with temperature) and on the generative length (optimum response to temperature). However, internode appearance rate was not affected by temperature. Number of flower heads showed a positive linear relationship with TDM. Therefore, by simulating TDM the number of flower heads can be predicted. TDM was simulated based on the intercepted photosynthetic active radiation and light use efficiency. The reaction time showed a quadratic response to temperature, with a maximum rate of progress to flower at 23°C (10 days delay at 18°C). These modules need to be validated to form the basis of a year-round decision support system for Kalanchoe.