A five-point penetrometer with GPS for measuring soil compaction variability

• A robust five point penetration resistance system was designed and developed combined with a GPS receiver.
• High soil compaction variability exists even in small experimental fields.
• The five point penetrometer was able to explain the behavior of five different tillage methods.
• Precision subsoiling could be planned by soil penetration resistance maps.

Measuring soil compaction is a factor of interest to monitor soil fertility, which plays an important role in crop production cycle. Soil penetration resistance is the most commonly used method to measure soil compaction. It is fast and simple although it presents important limitations due to its close relationship with soil water content and the existence of high variability in the field, which requires increased number of samples that is effort demanding and time consuming. In this work, a fast and robust 5-point penetration resistance system was developed attached on the tractor three point hitch using load cells and combined with a GPS receiver. An ultrasonic sensor to monitor the penetrating depth was also attached. A software program using Microsoft Visual Basic was developed for data acquisition. Security pins and software alarm was added to secure the equipment safety when stones or soil harder than a limit was encountered. The system was successfully tested in an experimental field, where five tillage methods were studied, including no tillage. The results indicated the system’s ability to recognize compacted soil layers and depict the spatial variability.