Mobility of herbicide microcapsules in saturated granular media

The mobility of the microcapsules in saturated granular media was estimated on the basis of conventional breakthrough experiments in vertical columns packed with sands for various physical and chemical conditions. Four types of microcapsules have been tested, all of them were found to have reasonable mobility in clean quartz sand, but not in sandy soil. The immobility in the sandy soil was attributed to some production deficiencies in terms of shape, size and quality of the coating surface. The size of the microcapsules should be considerably smaller than those produced with an order of magnitude of a few micrometers. They should also be more spherical and with a smoother surface. The addition of a proper dispersant had stabilized the microcapsules suspension, and facilitated their transport in the sand. A major flow factor affecting microcapsules mobility is the water flux. The microcapsules should be applied at a high irrigation rate, which also implies a high water content in the soil profile. Considering solely the mobility aspect, it seems that the prospect for successful application of the new method for weed control is limited to granular soils with a high hydraulic conductivity at/or near saturation. However, for the time being the most limiting problem is the production of quality microcapsules with good physical and chemical properties.