After last year’s flooding, many farmers may be dealing with soil compaction. Not all soil compaction is the same. Knowing how to identify the four main types of soil compaction can help you diagnose and solve the problem on your farm.
True hardpan generally occurs only in Solonetzic or heavy clay soils which have a very dense soil layer high in clay and sodium. This hard, dry Solonetzic layer can be as shallow as 10 centimetres or can extend to a depth of 75 cm. It restricts water movement during wet conditions, which results in poor topsoil quality, crusting problems and soil erosion.
To manage Solonetzic soils, timing of tillage and seeding operations with respect to moisture conditions is important. When the soil is too wet, tillage implements don’t work. Conversely, when the soil is too dry, tillage implements have difficulty penetrating the soil and cause hard lumps when they do. Deep plowing or deep ripping of Solonetzic soils is often necessary.
2. Surface soil crusting
Surface soil crusting is usually caused by a combination of soil tillage and raindrop or irrigation water impact. The crusted soil can restrict both water infiltration into soil and emergence of germinating crops, reducing plant stands and potentially affecting yield.
Crusted soils are easy to diagnose by examining the soil surface, which may have a plate-like, horizontal layered structure of crust.
A short-term emergence solution for soil crusting after seeding might be a light harrowing or rolling with packers to gently fracture the soil crust after seeding, to aid in seedling emergence through the crust.
The best way to prevent soil crusting is to minimize tillage and leave a protective layer of residue on the soil surface to absorb the impact of water droplets. Including a forage in the crop rotation or using direct seeding practices will increase soil organic matter and make the soil more resistant to breakdown. In irrigated fields, water application should be managed to ensure the infiltration rate of the soil is not exceeded.
3. Subsurface compaction
Subsurface compaction occurs in the layer of soil just below the depth of tillage and is worsened by wet conditions or in soils with high silt or clay content. It occurs when soils are cultivated repeatedly at the same depth and is caused by the weight of equipment, producing a compacted layer about two to three centimetres thick.
Subsurface compaction can be identified by using a shovel or trowel to shave away the tilled surface soil until the compacted layer is exposed. If plant roots are growing horizontally along the surface, roots are having difficulty penetrating the layer.
Most compacted soil layers should break down with annual freeze-thaw and wetting-drying cycles. If they persist, the soil may need tillage or sub-soiling to break up the compacted layer. This should be done when soil is dry, there should be some residue left on the surface to prevent erosion and care should be taken not to mix subsoil with topsoil. This type of tillage is a temporary fix, however, and farmers should also consider tweaking crop rotation to include taproot and fibrous root crops, reduced tillage and direct seeding for a more permanent solution. For soils that must be cultivated, varying the depth of tillage and avoiding working wet soils will help. Deep ripping equipment is not recommended for this type of soil compaction.
4. Wheel traffic-induced compaction
Heavy farm equipment can exert considerable weight onto the soil surface and, consequently, into the subsoil. The effect of equipment weight can penetrate down to 60 cm when soils are moist.
Wheel track compaction problems are identified by reduced crop growth in wheel track areas of the field. Dig up and examine plant roots from healthy, unaffected crop areas as well as those from problem areas to see if growth is being affected by compaction. Plants from compacted areas may have malformed or restricted root development that is confined to the top layer of soil.
Wheel-induced compaction can be prevented and managed through good agronomic practices, although deep tillage may sometimes be necessary. To prevent the problem, avoid having equipment repeatedly use the same wheel tracks to enter or leave the field. Avoid traffic on the land when soils are quite moist and load seeders and unload combines on the headlands to reduce traffic in the field.
Use deep-rooted crops, such as alfalfa, to penetrate the compacted soil layer and help utilize natural wet-dry and freeze-thaw cycles to mellow the soil.
Where wheel traffic has caused compaction to a depth of 30 to 50 cm deep tillage may be necessary, but this method will not generally help with compaction at a depth below 50 cm. Soil must be dry and equipment operators should try to leave as much residue on the surface as possible. Subsoilers or deep rippers can cause mixing of soil layers, which should be avoided. Mechanical deep tillage is only a short-term solution to soil compaction and is expensive. In the long term, agronomic practices are a better solution to minimize wheel traffic compaction.