Analysis and simulation of growth and yield of cut chrysanthemum

<strong><em><font size="3"><p>Key words</strong></em> : chrysanthemum, crop growth, development, explanatory model, expolinear growth, dry mass, dry matter partitioning, fresh mass, leaf area index, light interception, light use efficiency, plant density, season, simulation, validation, year-round.</p><p> </p><p>Seasonal variation in daily light integral naturally leads to seasonal variation in production and plant quality in year-round cut chrysanthemum ( <em>Chrysanthemum</em> , Indicum group). Growers try to deliver constant product quantity and quality throughout the year by adapting plant density, day length, duration of long-day periods and supplementary lighting. Optimising crop management is very complex and requires a great deal of knowledge that is best represented by a generic model. There is, however, no such model available and there is also a lack of information on the dynamics of crop performance, i.e. dry mass production and leaf area index.</p><p>In this thesis, growth and yield of cut chrysanthemum were analysed and quantified, as related to radiation, planting date and plant density. A generic model, CHRYSIMv1.0, was derived from an existing photosynthesis-driven model, calibrated and validated for year-round cut chrysanthemum.</p><p>Final plant fresh and dry mass and number of flowers per plant decreased with plant density and this decrease was larger in summer than in winter. The observed variation in plant fresh mass can be described by a linear relationship with cumulative incident photosynthetically active radiation (PAR) per plant.</font><font size="3">Dynamics of aboveground total dry mass per m <sup>2</SUP>(TDM) and leaf area index (LAI) were well described by the expolinear growth equation. Moreover a modified expolinear growth equation, formulated as a function of accumulated daily incident PAR was used to derive the light use efficiency (LUE, g MJ <sup>-1</SUP>) for closed canopies. LUE showed a hyperbolic relation to daily incident PAR and LUE was used to determine the maximum crop growth rate (g m <sup>-2</SUP>d <sup>-1</SUP>) at closed canopy. However, it was hard to generalise growth and yield of cut chrysanthemum under a wide range of crop growing conditions and in this approach measured LAI is still required as an input. These limitations lead to the development of a model for predicting LAI and use of it with a generic model for predicting growth and yield of year-round cut chrysanthemum.</p><p>Dynamics of LAI can be simulated by the combination of increase in leaf dry mass (LDM) and specific leaf area of new leaves (SLA <sub>n</sub> ). Dynamics of LDM could be adequately described using a Gompertz function to describe dry mass partitioning to the leaves. SLA <sub>n</sub> was linearly related to the inverse of the daily incident PAR, to temperature and to plant density. Dynamics of LAI were satisfactorily simulated for independent experiments and for commercially-grown crops.</p><p>CHRYSIMv1.0 was validated, using measured LAI and dry matter partitioning to the organs as an input, to check first possible errors in crop photosynthesis, maintenance respiration and dry mass conversion efficiency. Global radiation outside, inside greenhouse temperature and CO <sub>2</sub> concentration were also input to the model. Simulated TDM was equal to measured TDM in summer (natural light) only, whereas a large under-estimation occurred at constant shade, and in winter. At low light LUE was largely underestimated by CHRYSIMv1.0. Calibrating the parameters of the photosynthesis light response curve of the leaves, i.e. initial light use efficiency,<FONT FACE="Symbol">e</font>, and maximum leaf photosynthetic rate, P <sub>gmax</sub> , based on one experiment resulted in largely improved simulations of TDM in all experiments, but unrealistic parameter values. Finally some limitations for application of CHRYSIMv1.0 are discussed in this thesis