PREDICTING LEAF AREA OF THREE GREENHOUSE CROPS USING PAR AND TEMPERATURE
Leaf area ratio (LAR), defined as the ratio of leaf area over plant dry weight, affects crop relative growth rate, hence, modelling LAR is of prime importance for the simulation of crop growth. Leaf area index (LAI) (reflecting LAR) represents the area of photosynthesising and transpiring organs. Therefore, it is important to predict LAI accurately for estimations of crop canopy photosynthesis and transpiration. LAI can be either measured or calculated using photosynthesis driven crop growth simulation models. The sophisticated and expansive instrumentation for monitoring LAI and the many parameters of the crop growth simulation model make on-line measurement and simulation of LAI not practical in greenhouse crop and climate management. Temperature and Photosynthetically Active Radiation (PAR) are important climate factors affecting crop leaf growth. The effects of both temperature and PAR on crop leaf growth were quantitatively investigated with an experimental study. The experiments on cucumber (Cucumis sativus), tomato (Lycopersicon esculentum Mill.), and muskmelon (Cucumis melo L. var. reticulatus Naud.) with different cultivars and sowing dates were conducted in greenhouses in Nanjing and Shanghai during 2002-2005. The concept of Product of Thermal Time and PAR (PTTP) and its calculation method were proposed. Then the following quantitative relationships were determined from the experimental data: number of appeared leaves per plant versus accumulated PTTP after the first leaf appeared on plant; leaf elongation rate per unit PAR and mature leaf area as functions of leaf rank, and leaf area as a function of leaf length. Based on these relationships, a LAI prediction model was developed for the three studied greenhouse crops. Independent experimental data were used to validate the model. The results show that the model gives satisfactory predictions of canopy LAI of the three greenhouse crops and the prediction accuracy of this model is significantly higher than that of the growing degree days and specific leaf area based models. The model developed in this study can predict LAI using air temperature, PAR, date of appearance of the first leaf, planting density and the number of removed old leaves.
Luo, W., Dai, J., Li, Y., Yuan, C., Chen, Y. and Ni, J. (2006). PREDICTING LEAF AREA OF THREE GREENHOUSE CROPS USING PAR AND TEMPERATURE. Acta Hortic. 718, 589-598
thermal time, model, management, photosynthesis, cucumber, tomato, muskmelon