Every good action movie needs a compelling villain, and it’s usually someone that we can relate to but also despise with the very fiber of our being. There would be no Batman without the Joker, no John McClane without Hans Gruber, and there would be no James Bond without Ernst Stavro Blofeld. The problem is we have a villain in your fields right now which affects every interaction between your plants and the soil, and that villain is excessive compaction.
Simply stated soil compaction occurs when soil particles are pressed together, reducing or eliminating the pore space between them. This “squeezing” of the pore space reduces the soil’s water infiltration rate and the ability for a soil to drain properly. If that wasn’t bad enough, the reduction of pore space also affects the soils ability to exchange gasses. This leads to a more anaerobic environment increasing the denitrification of our applied N. Excessive compaction increases the soil strength or the ability for a soil to resist being moved by and applied force, which in our case is roots.
There is always some level of compaction in our soils and in certain situations moderate compaction is ideal for us to maximize yields. For example; a slightly compacted soil will improve seed to soil contact and help speed up the rate of germination in the spring. Additionally, a moderate level of compaction may help reduce water loss from a soil due to evaporation, preventing the soil around roots from drying out. This is the very reason we talk so much about closing wheels and ground contact during the planting season, to ensure the “right” amount of compaction.
Excessive compaction above about 74lbs per cubic foot starts to impede root growth and limits the volume of soil a plant can access. This limitation leads to a reduction in the plant’s availability to take up nutrients and water. That adverse effect of reduced water flow and storage combined with the reduced ability for the plant to take up Nitrogen, Potassium and Phosphorus is the more serious than the direct effect on root growth itself. The reason why compaction is such a villain is by the time we see the symptoms of nutrient deficiencies the damage has already been done, and sometimes we place the blame on something other than the compaction itself being the root cause.
In most cases, everything we do causes compaction, so in essence, we created this villain ourselves. Tillage operations at the same depth year over year at the same depth cause a tillage pan, and it doesn’t matter what kind of tillage it is. Wheel traffic, by far this is the most common cause of compaction, because of all the traffic you have across your fields today. Seventy percent of wheel track compaction comes in the first pass, which is why controlled traffic becomes so important. Minimal crop rotations cause compaction because the rooting depth of those crops is typically the same from year to year. Lastly, irrigation and all the raindrop impact has a role in surface compaction, essentially sealing the soil at the surface.
Just last week I heard someone say, “I know I have compaction, but it will probably freeze out this winter,” friends, that is one of the bigger myths in our industry because we don’t get enough freeze/thaw cycles to reduce anything more than the surface compaction. Deep tillage/Subsoiling isn’t always the answer either if you are in a rainfed area, the action of subsoiling may actually be detrimental to future yields. When subsoiling we have to make sure we are at the right depth and getting adequate shatter. The best strategy for compaction is avoidance if at all possible because the best way to stop a villain is not to create it in the first place.