Factors affecting the significance of macropore flow for leaching of agrochemicals.
This paper attempts to summarize the most important factors which regulate the impact of preferential flow on leaching of agrochemicals, based on a range of long-term field and lysimeter experiments on pesticides, nitrate and phosphorus. In particular, the role of chemical properties, biological and chemical transformations, and physical exposure to preferential flow pathways are stressed, as well as differences in soil type and the significance of the highly transient nature of climatic boundary conditions. A simple two-region model (MACRO) has been used as a tool to quantify the effects of macropore flow for varying solutes under different agroenvironmental conditions. Some examples are presented which demonstrate that macropore flow can either increase or decrease the leaching of agrochemicals depending on the nature of the solute and the location of the solute in relation to the flow pathways.