Researchers at the ARS (Agricultural Research Service) of the USDA have designed and are evaluating a special sensor that attaches to a tractor and measures soil compaction at six different depths as it moves across a field. Compaction is a key factor in soil productivity. For roots to thrive, the soil must provide the right amount of water, as well as have good texture and the correct amount of nutrients. The level of soil compaction is equally important. If the soil is too compacted, there will not be enough pores to allow the roots to respire properly. If the soil is too loose, nutrients will leach through the root zone too rapidly and will not be useful to the plant. Soil compaction is primarily caused by Nursery machinery and equipment (or monoculture) and can vary widely over the production areas, thus contributing to different yields in different areas. Researchers and consultants have traditionally used a cone penetrometer to measure compaction in the field. The instrument is pushed into the ground to measure compaction at a single location. Using a penetrometer to map compaction variations within a field requires a lot of effort and the data must be collected at many locations. Scientists and farmers would benefit from the new instrument, which is easier to use and gets better results. It will show the grower where compaction may be a problem within a field. This new information should also help to interpret plant productivity and uniformity of production. ARS is the US Department of Agriculture's chief scientific research agency. www.agriworld.nl www.ars.usda.gov