Soil compaction can occur through heavy vehicle traffic. I attached a picture (see below). There are three samples approx. to 5m distance to each side of a paved road. Vehicle traffic is sprodically (few times in a year, e.g. at harvest).
Do you think at the sampling points in the soil (0-30-cm depth) compaction could have occurred through vehicle traffic? The blue area is untilled, i.e. more aggregate stability. The grey part is tilled, i.e. soil aggregate structure is loose.*
*The thing is, I noticed very high accumulation of soil organic matter under the blue area which also had lots of vegetation one yr prior to sampling -- unlike the grey area which has been cropland for long time. It is said that compaction can suppress mineralization of soil organic matter because of lower aeration in soil which inhibits decomposer communities.