Tilth Indicator

How can you assess the impacts of farming practices on soil structure? That is the challenge organic inspectors face at each farm visit. The organic certification standards require that soil structure be maintained and/or improved. Inspectors must verify that this is being done.

I knew in 1991 on first becoming an organic inspector, after 15 years working in conventional agri-food, that this assessment was not easy to do. There were no good field indicators back then that could be used.

It became a personal obsession to find something that could help assess soil structure out in the field. Decades later it became clear that what was discovered while working as a soil research officer, could be useful for organic inspectors, farmers and others.

First let us get something clear. Good soil structure or tilth means a stable pore space structure. Healthy soil lets crop roots grow deep down, searching for available water and nutrients. The pore spaces make this possible. A noted soil health researcher, Dr. Sam Weil from Maryland University, made a suggestion at a field day for organic farmers. He said growers could straighten out a thick metal coat hanger, then walk around their fields and see how far down they could push the metal rod. That seemed like something that could be done.

My last few years as an active organic inspector found me using this metal probe during farm visits. Later, it was used with the farmers we bought food from at the farmer’s market. They kindly let me come out to their fields and test out various field indicators. Recently, we have added colour to the metal rod. This makes it easier to judge depth out in the field. The colours also help relate depth to compaction back to key research findings. This helps the farmer interpret what they are seeing out in the field.

The depth to compaction probe is designed to assess the impacts of farming practices on soil structure or tilth. This is also a handy way to assess soil health in a field or garden plot; a growing box or a pot on a balcony. Titlh is a physical quality of the soil that also points to the chemical and biological components of soil, as well.

Chemical soil tests are great for selling chemical fertilizer. I used them while selling chemical fertilizer to large grain farmers, at a big grain elevator in north east BC. They can also be useful for creating a baseline of the farm to compare progress to. I went through these tests with many organic farmers before realizing that they were little understood and of little help in building up soil structure.

The depth to compaction probe pictured below is a simple but instructive way to assess soil health while out in the field. The colours point back to research findings about how much topsoil exists in a field. The more depth of topsoil, the healthier your soil is. Depth to compaction is another way of saying depth of topsoil. Several research reports list 4 inches or less of topsoil being associated with conventional tillage and summerfallow. Our probe has the first 4 inches coloured RED, so farmers get immediate feedback that they can interpret themselves. The top colour is GOLD because if your field has

from 18 – 24 inches depth to compaction, then you can get profitable yields without needing to add fertilizing materials each year.

Our company focuses on taking research and making it easier for farmers to apply it on their farm, in their fields. The tilth indicator / depth to compaction probe is one of 5 field indicators that have been developed to help farmers and gardeners assess the health of their soil.

We also have things they can do to capture carbon and build healthy soil.