Soil herbicides kill plants via root uptake. The use of soil herbicides can be made more sustainable by adjusting the dosage to the local soil condition. This so called Variable Rate Application (VRA) is the core of Precision Farming. Soil herbicides often play an important role in weed control strategies in conventional arable farming. Broad field uniform application is by far the most common application method.

However, with increasing advances in sensing and spray technology, and the development of Decision Support Rules (DSR), the shift to VRA application is likely to occur. Soil applied herbicides are sprayed around crop-emergence and kill germinating weed seeds in the top few cm of the soil. The activity in the soil is regulated by physico-chemical characteristics of the herbicide, and weather and soil conditions. For the VRA application of soil herbicides, the relation between the herbicide and relevant soil properties  needs to be known and is described by the DSR. Today, at least three types of soil sensors can be used to determine soil properties such as organic material or clay content. The DSR can be obtained by greenhouse experiments, on-farm trails, bioassays, literature reviews, modelling, or a combination of these approaches. A detailed map and data on the spatial variation of the relevant soil property is required. These can be obtained a.o. by sensing or extensive sampling and subsequent interpolation. Combining DSR and soil map provides the potential spray map. The farmer adjusts the map in the Farm Management System by taking into account routing and spatial resolution of the spray equipment, resulting in the task file. The variation within the field, the DSR, technical characteristics of the spray equipment, and the route planning within the field together determine the possible reduction in the applied herbicide. The first steps to implement VRA of soil herbicides have been taken on pioneering farms in the Netherlands within the PPL program and is currently being further developed  within the research program IJKakker. First results of on farm research show that with this VRA system, level of weed control remains good while herbicide side effects on the crop are minimized.