1. Sand soils
Sand soils are often dry, nutrient deficient and fast-draining. They have little (or no) ability to transport water from deeper layers through capillary transport. Therefore, tillage of sandy soils in the spring should be kept to a minimum in order to retain moisture in the seedbed. The nutrient- and water-holding capacity of sand soils can be improved through adding organic material.
2. Silt soils, 0-10% clay
These soils differ from sand soils by having a greater tendency to form a crust, which is often very hard. If they are over-tilled, they can become compact and this decreases their ability to infiltrate water in wet periods. In dry conditions they can become hard and difficult to till. However, they are generally easy to till and can store considerable amounts of water. They require good reconsolidation, but tillage in wet conditions should be avoided.
3. Clay soils with 10-25% clay
These soils differ from those described above in that crusting can be very severe. The crust is often so hard that it has to be broken up. With low contents of clay and organic material, aggregate formation is often poor.
4. Clay soils with 25-40% clay
These soils have a good ability to transport water by capillary action from deep layers but the rate is slow, so plant water requirements are not met through capillary water. These soils are darker in colour and soil aggregation is more distinct. Aggregation decreases the risk of crusting. These soils must be tilled at the correct water content in order to be easily cultivated. There is a risk of clodding if conditions are too dry, or of smearing if they are too wet. These soils have a good ability to improve their structure through the action of climate, roots etc.
5. Clay soils with 40% clay
Heavy clays have a very high water-holding capacity, but most of the water is tightly bound and not available to plants. The humus content is often higher than in other mineral soils. They do not form a crust when they dry. These soils have a very good ability to improve their structure through e.g. freezing/thawing and drying/wetting. In cold winters the clay freezes apart and forms a very favourable aggregated structure in the topsoil layer. If the clay dries out without having been frozen, it can become very stiff and difficult to work.
In the water-saturated state these soils can be sticky and very impermeable to water. Due to the high clay content, the nutrient content is very high. Heavy clays need a high degree of recompaction around the seed when they are dry, but not when they are damp and plastic. The risk with tilling them in wet conditions is that it leads to soil compaction.
Capillary = capillary water is water that can rise upwards in the soil within the fine pores through binding of the water molecules in the pores, adhesion, but also through attraction between water molecules, cohesion. Silty soils have high capillarity and combine a large height of capillary rise with a high rate of capillary rise.
Clay = clay is the smallest particle group, with an average particle diameter of less than 0.002 mm. See table "Particle size distribution" in chapter The building blocks of soil.