Estimation of growth and yield for single-stemmed rose ‘Vital’ in a single stem system

Abstract

In ornamental crop production, growth models as a function of environmental factors can be used as a valuable tool for predicting the timing of a phenological event for the average of a population, for the optimization of environmental conditions inside a growing system, and for making cultural decisions for increasing crop production. The feasibility of an expolinear growth equation was evaluated by predicting the crop growth of single-stemmed rose ‘Vital’ in a single stem system using recirculating nutrient solution. The objectives of this study were to determine a suitable environmental variable and growth parameters, i.e. maximum crop growth rate (Cm), maximum relative growth rate (Rm), and the lost time (tb) for expolinear growth equation using biomass data obtained from 4 experiments with different seasons [cut on Oct. and Nov. in 2004 (Expts. 1 and 2), and Apr. and Jun. in 2005 (Expts. 3 and 4)] and then to predict the crop growth based on an empirical model as a function of the environmental variable and plant density (plants/m2) using estimated parameters of the expolinear growth equation. The growth parameters were estimated by fitting the expolinear growth equation as a function of time, thermal units (TUs, °C·d), or daily incident photosynthetically active radiation (PAR, MJ·m−2·d−1) to observed the biomass per unit area (m2) using a nonlinear regression procedure with Gauss-Newton method. The use of TUs as a variable of expolinear growth equation improved the accuracy of the model and gave a better estimate of growth parameters as compared with those of time or incident PAR integral. Although the fitted expolinear growth equation effectively described the measured fresh and dry mass per unit area, we concluded that TUs was an appropriate variable of expolinear growth equation for single-stemmed rose ‘Vital’ considering some advantage, such as a cheap and easy way for growers to measure the microclimate inside a greenhouse for cut-flower rose production. This study also investigated the effects of TUs and plant density (67, 89, and 107plants/m2) on the growth of single-stemmed rose ‘Vital’ in a single stem system by adjusting the expolinear equation. The growth parameters, Cm, Rm, and tb were estimated by fitting the expolinear growth equation to the measured dry mass measurements obtained from 3 experiments (Expts. 1, 2, and 3) at three different plant densities. Parameters Cm and tb showed a curvilinear relationship with plant density over three experiments and were fitted to the quadratic function. The Rm was substituted with the mean value of the estimated values at each plant density, 0.0082, because there were no significant differences in Rm values among plant density treatments. The estimation of dry mass per unit area by the expolinear growth equation as inputs of TUs and plant density agreed well with the validation data, but the model tended to overestimate dry mass per unit area. The measured dry mass showed a linear relationship with fresh mass regardless of plant densities. The shoot fresh mass per m2 was estimated by an empirical relationship between shoot fresh mass and dry mass using the estimated shoot dry mass. The estimated and measured shoot dry mass and fresh mass showed a reasonably good fit with 1.142 (R2 = 0.988) and 1.168 (R2 = 0.976), respectively.