The Effects of Tillage on Aggregate Stability
As I’m out and about promoting soil health at field days, crop tours and conferences I typically run into a farmer or two that think what I’m talking about is voodoo science and this whole no-till/soil health thing is a bunch of malarkey.
They claim that you need to “open up and fluff up the soil with tillage” so it can take in moisture and that no-till just makes the ground hard making it difficult for water to get through.
Tradition may make you think that is the case.
After all farmers have been using tillage since almost the beginning of time and it is what dad and granddad did. But the opposite is true.
To start with, most tillage creates compaction layers that only allow the moisture to get into soil just a few inches before it begins to runoff or pond.
But more importantly tillage destroys soil aggregates, and the soil biology that helps form them.
A soil aggregate is a whole bunch of individual soil particles held together into bigger sizes by biological glues that soil organisms, like fungi, bacteria and earthworm secrete. By the way these soil organisms rely on a living plant to survive.
Decomposing soil organic matter also provide organic glues. These bigger “clumps” of soil provide pore spaces so when it does rainwater can get into the soil.
Think of it of how water well works. We use large pieces of gravel and rock to fill in behind the well casing to provide large pore spaces for water to get into the well.
If we would use something smaller in size, like clay particles, there would be smaller and fewer pore spaces so very little water would get into the well. Same goes for the soil.
The fewer and smaller pore spaces the less water infiltration there will be.
In addition, soil particles easily break away from each other when water enters an aggregate with low stability. These soil particles fill surface pore spaces and form a hard crust on the soil surface when the soil dries.
Water has difficulty penetrating this crust and it typically runs off, which causes erosion. The crust can also restrict seedling emergence.
In western Kansas dryland cropping systems it’s all about water. The more we can capture and store in the soil profile the better chance we have a growing a good, productive crop.
Stable soil aggregates, that don’t break apart when water enters them provide more pore spaces for water to enter. This also increases the soil’s water holding capacity. Good aggregate stability also helps in root development, which helps the plant take up more water and nutrients. The soil is also more resistant to erosion.
So how do we improve our soil aggregate stability? The simple answer is to reduce tillage. Excessive tillage physically breaks down soil aggregates and disturbs the soil organisms that secrete the glues that hold soil particles together.
Over time it also depletes soil organic matter which is also important to aggregate stability. I get that an occasional tillage operation may be necessary and the best tool to use for the circumstance.
But when it comes to improving the water infiltration and increasing the soil’s water holding capacity tillage is not your friend.
For more information about this or other soil health practices you can contact me at firstname.lastname@example.org or any local NRCS office.