Estimation of Canopy Light Interception of Lettuce (Lactuca sativa L.) Grown under Reflective Surroundings and Artificial Lights with Different Blue and Red Compositions in Plant Factory

Abstract

It is one of the most important topics among researches related to crop growth model to construct an accurate method for the estimation of crop light interception. The light environment is highly modified in recent horticultural facilities by the abundant use of artificial lights and reflective materials. Due to the difficulties in quantifying the effect of various light environmental factors, outstanding progresses have not been made in the development of models to estimate crop light interception available for the facilities. The aims of this study are to construct a model for the estimation, which reflects the critical light environmental traits of the facilities (Chapter I), and to verify the reliability and applicability to the existing crop growth model (Chapter II). The light environment of a plant factory was analyzed and a new model was constructed based on the result in the Chapter I. The model estimations for lettuce light interception were compared to actual crop light interceptions, which were measured and calculated using artificial lettuce and modified Nicolet model, and applied to original Nicolet model to investigate the effect on the entire crop growth model at Chapter II. As a result, ambient light environment, such as ground reflectance and the proportion of diffuse light, was shown to have significant influences on overall crop light interception. And, it was possible for the new model to estimate the immediate and accumulative crop light interception with a maximum RRMSE of 11% and to complement original Nicolet model for the accuracy of estimation. This ultimately indicates that it is required to change a conventional paradigm of light environmental control in the plant factory or growth chamber which manages the light environment with a single factor of initial light intensity. In addition, it suggests a simple methodology available for recent horticultural facilities to quantify the effect of changes in the light quality on crop light interception with a single factor of b/a ratio, and the ideotype canopy.