A SIMULATION MODEL ON LEAF COLOR DYNAMIC CHANGES IN GREENHOUSE MUSKMELON UNDER DIFFERENT CULTIVARS AND ORGANIC FERTILIZER RATES

Abstract

With the development of digital agriculture, the visualization expression of the plant growth process is very important. Quantifying the dynamic process of leaf color is an important task for realizing virtual and digital plant growth. Based on time-course observations on leaf color changes at different leaf positions of greenhouse muskmelon under different organic fertilizer rates with five muskmelon genotypes cultivars, we developed a simulation model on leaf color dynamic changes in muskmelon in relation to ΣTU (Accumulated Thermal Units). The results showed that the leaf color changes at different leaf positions accorded with a linear equation in growth initial stage and growth senescence stage with ΣTU; and kept a steady value in growth function stage, which showed remarkable differences under different genotypes, cultivars and organic fertilizer rates. The growth dynamics of leaf SPAD could be described with a subsection function. In addition, the effects of organic fertilizer rates on leaf color were quantified through the effectiveness values of leaf nitrogen concentration in relation to SPAD. Then, the RGB values were further predicted from the changing SPAD. The model was validated with the independent field experiment data involving different muskmelon cultivars and organic fertilizer rates. The average RMSEs between the simulated and observed SPAD dynamics at three leaf color phases on different leaf positions were 11.65, 9.39 and 10.51, respectively. The results indicate that the present model has a good performance in predicting leaf color changes at different leaf positions in muskmelon, and thus lays a foundation for further constructing a digital and visual muskmelon growth system.