Modeling Canopy Carbon Gain and Water Use Efficiency in Response to Kaolin Residue Amounts in Fruit Trees

Kaolin particle films are commonly used in horticultural crops to repel insects, and reduce heat stress and solar injury. Additional benefits of kaolin include improved canopy carbon assimilation, water use efficiency, crop yield, and produce quality. Recent studies as well as our previous research have shown that increased reflectance by kaolin particle films within the canopy are an important part of the underlying mechanisms accounting for the physiological enhancements at the canopy scale. Here, using a process-based modeling approach, we demonstrate that the enhancement in canopy carbon gain depends on kaolin residue amounts and that there is an optimal residue amount which maximizes canopy carbon gain and water use efficiency. We further illustrate that the optimal residue amount of kaolin varies with macro- and micro-climatic conditions, leaf photosynthetic and stomatal characteristics, and canopy architecture in fruit trees. We test these model predictions using the results from a 5 year field experimental study in which biomass and fruit yield were enhanced as a result of applying 12% kaolin particle films compared to 0 or 3% treatment in fully mature ‘Empire' apple trees in Kearneysville, WV. These empirical data support the model predictions that the optimal residue amount may be relatively high compared to what is commonly practiced in the field. We then apply the model to identify optimal kaolin residue amounts under various environmental conditions at different geographic locations using apple as an example.