Introduction
After the dry period we have experienced for the past month and with welcomed rain now falling, it is an ideal time to think about aeration. There can be some confusion around aeration and the types of aeration to do and sometimes people often wonder about the benefits. Here are some hints and tips we have found over the years at Plant & Soil Solutions that might help with some of the myths.
Soil Health
Firstly, soil is technically meant to be 25% air, something we can’t see or touch but is the most important part of life – oxygen. Everything needs air to flourish and our soils are no different. Worms and the majority of microbes flourish, if they have sufficient air.
The most important thing before talking about the types of machines or the time of year to complete aeration is that conditions have to be right, otherwise you can do more harm than good. When thinking about aeration and letting air into the soil, it is about opening up the soil and creating small cracks through the soil structure whilst not disturbing the root structure too much. The soil needs to be dry to do this, but the fear on lighter, dryer land is that if a very dry period comes, it could accelerate the soil down to a depth. In this case, August and September can be safer months to do aeration on this dry land.
Types of soil compaction
In Ireland we suffer from different types of compactions that negatively impact the amount of oxygen in our soils.
- High rainfall can negatively impact soil structure, particularly soils that have a low cover of grass and poor rooting.
- The constant pounding from the rain all winter can compact soil.
- We then have compaction from heavy machinery and maybe heavy machinery in less-than-ideal conditions.
- And finally, compaction from livestock. This is one that is often overlooked because people usually automatically think of big heavy machinery causing the compaction.
The difference with all these situations is how we treat them.
How to treat and alleviate soil compaction
I would group the rainfall and livestock compaction normally together because surface compaction is usually the problem. Having adequate drainage in place is the first port of call, then when soil is dried out sufficiently using a spike aerator to open up the capping on the surface of the soil is usually enough. These machines have blades that penetrate the soil to 15cm (6 inches) and normally the machine has a cranked shaft so the blade enters and leaves the soil at a different angle causing small cracks to form down through the soil profile.
A question that is often asked is how I know when the soil is dry enough? I would advise to check the slot that was left by the aerator – it shouldn’t be smooth or smeared on the sides and there should be loose friable soil at the bottom of the slot. This aeration can be repeated a second time in the year if the soil is badly capped.
The second type of compaction caused is by heavy machinery. This can happen after spreading slurry early in the spring or if weather isn’t favourable at silage cutting time. Of course, the best advice is always to stay out of fields when conditions aren’t ideal but for various reasons, this might not always be possible.
In this scenario you need to dig a hole and measure how far down the compaction is. If it is more the 15cm down and if the soil layers are changing in colour, then a legged sub-soiler/sward lifter needs to be used. The target with this machine is just to go below the depth of the compaction, not just how deep the machine will go! This can cause some soil/sward disturbance so it’s advisable that it is done later in the summer as the sward has all winter to settle back down.
Benefits to soil health
After all this work is completed, what results should we expect? I would always look at the benefits below ground before looking above ground.
- Increased worm activity
- Increased microbial activity
- Increased rooting which brings more nutrients from a deeper level in the soil up into the plant
- Increased nutrient use efficiency i.e., applying nutrients to a soil that’s functioning better
- Thicker denser sward
- Better water infiltration, so when high rainfall does happen in the future the soil is able to process it quicker and more efficiently