Controlled release technology: development of a slow release systemic repellent for the protection of tree seedlings from deer
Modern forestry practices now include the use of many controlled release products, such as herbicides, pesticides fertilizers, superabsorbents, growth stimulants and animal repellents. Optimal use of these devices requires models that predict desirable release kinetics. Although some progress has been made in the development of empirical relationships between environmental data and pesticide persistence in soils, no workers have attempted to develop such models from first principles. Such a model is constructed in this study, and the model predictions are tested by comparison with the field results obtained following application of a slow release systemic repellent to tree seedlings.This deterrent device was designed in the study as an alternative to the chemical and mechanical protectants now available to prevent animal damage to tree seedlings. Selenium, the active agent, is absorbed through the tree's roots, transported to the foliage and thereafter volatilized as dimethyl selenide. This compound is the material responsible for the bad breath of humans who have eaten garlic, which is rich in the element. Eighty percent reduction of browse damage has been achieved by treatment of Douglas-fir (Pseudotsuga menziesii) seedlings with low-solubility selenium tablets.Foliage samples collected at various field trial sites treated with the tablets provide data with which to test the model of active agent transport through the soil/plant system. The success achieved in the prediction of foliar selenium content as a function of time demonstrates that it is possible to apply fundamental chemical engineering principles to this complex system. Thus it is now possible to use these concepts to engineer other controlled release delivery systems for applications in both forestry and agriculture, in which the essential physics of the transport process should be identical.
- Chemical engineering