Soil compaction is an annual spring time concern for farmers, gardeners and anyone else working on wet soils. But what is compaction and why is it such a concern?
First, think about what a healthy soil looks like. If you could dig up a column of healthy soil without disturbing it, you would find a balance between solids and pore space. The pore space would be partially full of water and also contain room for gases. The solid material would be a mix between minerals and organic matter. This combination of solids, liquids, and gases allows plant roots to grow, access minerals, and exchange gases with the atmosphere.
Now, think about taking that same column of soil and compressing it into a smaller space or volume. You would have the same amount of solids but less pore space. Furthermore, the solids that are there may have been crushed and are now smaller and packed tighter. We have effectively created a space where it is harder for roots to grow, to access water and nutrients, and to exchange gases with the atmosphere. All three of these are essential for healthy plant growth.
So how does compaction happen? Soil compaction can happen in any number of different ways – from driving heavy equipment on a field, having a hard driving rain on unprotected soils, or by humans and animals just walking. And it can happen at different locations within the soil – at the soil surface, below a plow layer, or on the side walls of planting furrows.
And what makes soils more vulnerable to being compacted? In general, in our area the wetter a soil becomes the more likely it is to become compacted if a pressure is applied to it. This is obviously a great concern in the spring when you combine snow melt and regular rainfall with the need to get crops planted. While getting crops planted in a timely manner is important for maximizing potential yield, creating compaction issues while planting that crop can offset all of the advantages of planting early.
Remember this basic rule of thumb for deciding if your field or garden is too wet to work in. Pick up some soil from the field or garden. Now press that soil between your hands and release. If the soil stays in a ball, then it is too wet. If it crumbles apart you are good to go. And remember, not all compaction is bad. We need good seed-to-soil contact for our crops to germinate well. We accomplish this in part by pressing the soil around seed that has been placed in a furrow. That is what press wheels are for on planters. The trick is to not press too hard and to wait for the correct environmental conditions so our compaction does good and not harm.