AOBPreview originally published online on September 26, 2003
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Annals of Botany 92: 697-708, 2003
© 2003 Annals of Botany Company
Using the Expolinear Growth Equation for Modelling Crop Growth in Year-round Cut Chrysanthemum
,31 Wageningen University, Department of Plant Sciences, Horticultural Production Chains Group, PO Box 9101, 6700 HB, 2 Wageningen University, Department of Plant Sciences, Plant Production Systems Group, PO Box 430, 6700 AK, Wageningen, The Netherlands and 3 Wageningen University, Department of Agrotechnology and Food Sciences, Farm Technology Group, PO Box 43, 6700 AA, Wageningen, The Netherlands
* For correspondence. National Horticultural Research Institute, RDA, Tap Dong Campus, protected Cultivation Division, 540-41 Tap Dong, Gweon-Seon Gu, Suwon, Gyeonggi-do, 441-440, Republic of Korea. E-mail leetag{at}hanmail.net Died before this paper was accepted.
Received: 31 January 2003; Returned for revision: 8 May 2003; Accepted: 31 July 2003 Published electronically: 26 September 2003
The aim of this study was to predict crop growth of year-round cut chrysanthemum (Chrysanthemum morifolium Ramat.) based on an empirical model of potential crop growth rate as a function of daily incident photosynthetically active radiation (PAR, MJ m–2 d–1), using generalized estimated parameters of the expolinear growth equation. For development of the model, chrysanthemum crops were grown in four experiments at different plant densities (32, 48, 64 and 80 plants m–2), during different seasons (planting in January, May–June and September) and under different light regimes [natural light, shading to 66 and 43 % of natural light, and supplementary assimilation light (ASS, 40–48 µmol m–2 s–1)]. The expolinear growth equation as a function of time (EXPOT) or as a function of incident PAR integral (EXPOPAR) effectively described periodically measured total dry mass of shoot (R2 > 0·98). However, growth parameter estimates for the fitted EXPOPAR were more suitable as they were not correlated to each other. Coefficients of EXPOPAR characterized the relative growth rate per incident PAR integral [rm,i (MJ m–2)–1] and light use efficiency (LUE, g MJ–1) at closed canopy. In all four experiments, no interaction effects between treatments on crop growth parameters were found. rm,i and LUE were not different between ASS and natural light treatments, but were increased significantly when light levels were reduced by shading in the summer experiments. There was no consistent effect of plant density on growth parameters. rm,i and LUE showed hyperbolic relationships to average daily incident PAR averaged over 10-d periods after planting (rm,i) or before final harvest (LUE). Based on those relationships, maximum relative growth rate (rm, g g–1 d–1) and maximum crop growth rate (cm, g m–2 d–1) were described successfully by rectangular hyperbolic relationships to daily incident PAR. In model validation, total dry mass of shoot (Wshoot, g m–2) simulated over time was in good agreement with measured ones in three independent experiments, using daily incident PAR and leaf area index as inputs. Based on these results, it is concluded that the expolinear growth equation is a useful tool for quantifying cut chrysanthemum growth parameters and comparing growth parameter values between different treatments, especially when light is the growth-limiting factor. Under controlled environmental conditions the regression model worked satisfactorily, hence the model may be applied as a simple tool for understanding crop growth behaviour under seasonal variation in daily light integral, and for planning cropping systems of year-round cut chrysanthemum. However, further research on leaf area development in cut chrysanthemum is required to advance chrysanthemum crop growth prediction.
Key words: Assimilation light, chrysanthemum, crop growth model, crop growth rate, expolinear, dry mass production, light use efficiency, plant density, shading, radiation use efficiency, relative growth rate.