Pennsylvania farmers are commonly using rye, triticale, and wheat for silage. These crops are typically followed by corn. When the spring is wet like this year’s, soil compaction caused during small grain silage harvest can negatively impact soil function resulting in problems for the following corn crop.
Soil is most sensitive to compaction when it is in the ‘plastic’ state – that is when soil particles easily slide over each other leading to a denser soil with fewer pores. If, by molding a handful of soil, you can easily form a ball – the soil is in the plastic state. When you traffic the soil at this moisture content, the larger pores get compressed and the porosity of the soil is reduced. This leads to reduced aeration, reduced water percolation, and increased penetration resistance which makes it difficult to achieve a good stand of corn, and inhibits root growth.
If the soil is wetter than the plastic state – when it starts acting like a liquid (also called ‘mud’), then you are going to create ruts which pose a big problem especially for no-till farmers. While ideally one would wait until soil has dried out enough so it is no longer in the plastic state, the urgency to harvest silage at the right growth stage leaves little flexibility for farmers.
I find it helpful to think about strategies that help avoid compaction, strategies that make the soil resist compaction better, and finally strategies that can alleviate (or help deal with) compaction.
Strategies that help to avoid compaction include staying out of the field when the soil is too wet (often not an option), reducing axle load below 10 tons by increasing the number of axles (or reducing the load), reducing contact pressure below at least 35 psi and preferably lower by increasing equipment foot print by using tracks or flotation tires at low pressures, and reducing the number of trips over the field.
Strategies that help make soil resist compaction better include using permanent no-tillage because surface organic matter content increases and the soil matrix becomes firm thus reducing the threat of creating ruts, and having dense root systems. The dense root system of a small grain silage crop does provide protection from compaction, acting like a geotextile below the soil surface.
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Although it is tempting to till, especially if ruts are created, you always have to remember that tillage makes your soil more susceptible to re-compaction in the future. So it is in your advantage to try to avoid using tillage to fix problems.
Finally, strategies to alleviate compaction include favoring soil biological activity such as earthworm populations and detrital or symbiotic fungal growth by reducing soil disturbance, leaving surface residue, and adding organic matter, using shallow tillage to level a field that has been rutted up, using subsoiling equipment that fractures the subsoil without causing soil inversion, and growing a following (cover) crop with aggressive root systems to take out compaction.
As always, there are trade-offs to make when considering your options. Some years ago I was notified of a great innovation by Mason-Dixon Farms in Adams County. They designed a carriage system on tracks that is connected to their chopper (see picture).
Mobile containers with expandable legs can be quickly mounted on the carriage. After the container is filled with chopped silage, it is parked at the edge of the field where trucks pick them up. The use of tracks reduces the footprint of the equipment and also helps reduce axle load.
The challenge right now is what to do if you have compaction – how to get corn planted at the right depth, avoid side wall compaction, and get the seed covered with soil. It is best if compacted soil is not too dry when planting into it to be able to penetrate it with the double-disk openers, although too wet means increased threat of side-wall compaction (see last week’s FCN).
Make sure you have enough weight on the planter and enough down-pressure on the planter units. In these challenging situations,as much as 300 to 400 lbs of downforce per planter unit may be necessary to enable furrows to be opened to the desired depth in moderately to severely compacted soils. Concentrate that downpressure on the double disk openers by not having unit-mounted coulters (frame-mounted coulters may be OK as long as you have enough weight on the planter frame).
Finally, use closing wheels that help break up the sidewall and do not cause excessive compaction on top of the seed such as fingered or posi-close wheels. Be aware of just increasing the pressure on steel or rubber closing wheels to close the seed slot.
Many of the things you can do to avoid and alleviate compaction as well as make soil resist compaction take time that you might not have this spring but perhaps this year causes you to think about some changes you can make in the future.