By Sjoerd Willem Duiker
The welcome rains have refreshed our crops but made the soil moist just prior to corn silage harvest. The soil compaction threat therefore has increased significantly.
Management should focus first of all on avoidance of soil compaction, and only use alleviation (after the problem has occurred) as an option of last resort. Some tips to avoid soil compaction:
- Monitor soil moisture – when you can make a ball out of the soil it is in the ‘plastic’ state and most compactible (this is called the ‘ball test’). If soil acts as a fluid (‘mud’) it is in the liquid state and you will cause deep ruts so that’s no good either. The challenge is that the corn needs to be harvested at the right moisture content for silage production so often flexibility is limited to respect soil moisture conditions. But it is still not a good idea to be out there the day after a significant rain storm.
- Limit traffic across the whole field as much as possible – it is amazing how much of the field can be trafficked during corn silage harvest, especially if trucks are driving back and forth next to the chopper. Because most compaction is caused in the first trip it is important to limit those second and third passes. Organize some traffic lanes that are ‘sacrifice areas’ – these can then be loosened later with a deep tillage tool without having to address the whole field.
- Use flotation tires on trucks and farm equipment. Many farmers use road trucks to haul their silage to the trench or silo. If these are mounted with normal road tires you are causing a lot of compaction. The surface contact pressure of these road tires is very high and causes a lot of surface compaction. When soil conditions are moist it is very important to use flotation tires.
- Adjust inflation pressure to lowest allowable pressure. Research has shown that the same tire inflated to high pressure will cause a lot more compaction compared to when it is inflated to low pressure. Therefore, use the lowest allowable pressure (but watch out for side-wall failure – which happens when a tire is underinflated). Check with your tire dealer to determine the right inflation pressure. Tire pressure in the field should be less than 35 psi, and preferably less than 20 psi.
- Use multiple axles – axle load impacts deep compaction. More axles help reduce deep compaction. Typically 10 ton axle load should be the limit to avoid compaction below 12 inches.
To alleviate the effects of compaction and prevent further compaction:
- Plant cover crops immediately after harvest. Don’t wait until your entire harvest is done, but have someone with a drill in the field plant the cover crops immediately behind the chopper to heal your soil. The moisture should get them started right away, and the roots alleviate soil compaction, while feeding soil organisms that help restore soil structure and porosity.
- Avoid tillage except when absolutely necessary (such as in high traffic lanes). Evaluate your soil structure using a shovel and the Pennsylvania Soil Quality Assessment Worksheet. You may be amazed to see great soil structure below what looks like a brick-surface in continuous no-tillage. The high surface organic matter content and roots from live crops and cover crops make the soil resist compaction and bounce back from its effects quickly. Although tillage looks like a great fix, it causes short and long-term harm by exposing the soil to erosion and by making the soil highly susceptible to re-compaction.
- Build organic matter. The proven practices to build organic matter are to use crop diversity and cover crops, have continuously living root systems in the soil, returning crop residues to the soil, adding manure with high-solid content, use compost, and using no-tillage.
No-till is now used on more than 60% of our crop acres in Pennsylvania and cover crops are becoming more and more common. By using these practices in combination with soil compaction avoidance strategies your soil can be maintained in excellent condition.