Development of Growth Prediction Method in Lettuce Plants Grown in a Plant Factory

Abstract

Fresh weight at the harvest of lettuce plants (Lactuca saliva L. cv. Red-fire-W) grown in a plant factory with fluorescent lamps was estimated by the automatic plant growth measurement system with a personal computer. Growth curves of leaf area, fresh- and dryweight of above ground parts from sowing to about 30 days in age showed an exponential pattern (r²=0.90 or higher) . It is most suitable to use an exponential regression function during young stage of the growth, considering a declining pattern in specific growth rate. Standard deviations at 6.1-5.4 were observed between the top fresh weight in 30 days after sowing and specific growth rate revealed by the regression curve of leaf area. On the other hand, standard deviations obtained by the leaf area estimated from the regression curve were 6.4-3.9. Further, standard deviations were 3.6-3.1, where the initial leaf area and specific growth rate were regarded as describing parameter. The growth of lettuce plant was quantitatively represented as the function of leaf area by image processing. Specific growth rate of leaf area of individual plants in young stage of the growth showed periodic fluctuation. As the plant grew from sowing, its cyclic period became longer. The leafing velocity is defined as a cyclic period of changes in specific growth rate.