Subsoiling is still considered one of the least popular cultivation procedures. This is probably largely due to its energy consumption, i.e. the cost of performing it, whether as a service or the purchase of a suitably large tractor and the consumption of significant amounts of fuel. Nevertheless, it is worth taking an interest in why subsoiling is important and what tangible benefits it brings to the fields.
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Plow sole
Subsoiling is often associated with the occurrence of the plow sole phenomenon. This association is absolutely correct. The subsoiler allows both to eliminate the plow sole and to prevent its formation. So what is this phenomenon and why is it unfavorable?
The plow sole is a layer of compacted soil that occurs below the cultivated layer, also known as the topsoil. It is formed in a place where the working elements of the tillage machines no longer reach, but the soil is still subject to the pressure of heavy machinery. During ploughing, we see it as the bottom of the furrow, which is often strongly compacted on compacted soils and thus clearly stands out from the regularly loosened topsoil. Importantly, to a lesser extent, but still, the plow sole can also form in the case of no-till cultivation, if it is carried out in strongly compacted soil for years at a constant depth.
This phenomenon is disadvantageous because a compact layer several or a dozen centimetres deep into the soil profile inhibits the infiltration and absorption of water, as well as the development of root systems, especially of deeply rooted plants. As a result, symptoms such as ponding after rainfall are visible on the one hand, and particularly pronounced problems with water shortages during droughts on the other. Moreover, the shape of plants, such as rapeseed or sugar beet, may be frail, and therefore the yield is significantly lower due to difficulties with proper rooting and, as a result, the uptake of nutrients.
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Subsoiling effects
As we have already established, the subsoiler is primarily used to combat the phenomenon of the plough sole. Its work contributes to the improvement of water-air relations, as well as the development of plant root systems. The removal of the compacted soil layer allows for the infiltration of rainwater, as well as the infiltration of groundwater towards the surface. Deeply loosened soil is also characterized by a greater water capacity, so in the event of a shortage of rainfall, the plants grown on it will later suffer from drought.
The removal of the plough sole is particularly visible in the case of cultivation of species with deep roots, such as the aforementioned rape or sugar beet. If they encounter an impenetrable barrier below the cultivated layer, i.e. approx. 25 cm into the soil, their growth and development will be weaker, which will negatively affect the yield. In the case of beet, phenomena such as forkhead or celeriac are described here, i.e. various types of deformations of the storage root resulting from the lack of possibility of development into the soil.
Excessive soil compaction occurs especially where it is exposed to particularly high pressure from heavy machinery. This occurs, for example, in the case of many dressing operations, harvesting beets, for example, with a heavy combine harvester in conditions of excessive moisture, but also on technological paths. The latter are places where heavy machinery passes over its tracks at least several times, often sinking deeper into the ruts, thus deeply compacting the soil. For this reason, subsoiling of paths should be an absolute minimum.
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How often to subsoil? When? Best after harvest
Subsoiling date and parameters
The post-harvest period is generally considered the best time for subsoiling. However, this is not a rigid time that should be adhered to at all costs. It is worth paying attention to the moisture content of the soil first. You should not subsoil either mud, because driving in heavy equipment will destroy the soil structure, or very dry "rock", where fuel and working element consumption will be huge, and the effect of the work will be questionable.
When it comes to timing, it is also worth mentioning the frequency of subsoiling in a given field. Of course, we should start with the justification for performing the procedure in a given place. It can be assumed that light soils, especially on sandy subsoil, do not tend to be excessively compacted, but the surest solution is to check whether there is a plough sole, and the easiest way to do this is to drive a metal rod into the soil or make a shallow excavation with a spade. Returning to the frequency, it can be easily determined in the above way, and theoretical assumptions say that it is worth performing subsoiling as a preventive measure no less than every 4 years, and in the case of technological paths and headlands, if not every year, then no less than every two years.
The key parameter of a subsoiler's work is of course depth. To determine it, first of all you need to know the depth of the plough sole, and ideally also its thickness, which will help to determine the soil outcrop. Then the machine should be set so that it works a few centimetres deeper than the lower limit of the plough sole, which will guarantee that it will be completely destroyed. Usually this value is in the range of 40-60 cm. In turn, if we do not know the thickness of the plough sole, it is most often assumed that subsoiling should be carried out 15-20 cm deeper than the deepest cultivation operation.
It is impossible to ignore the energy consumption of subsoiling. Cultivation to the aforementioned average depth of 40-60 cm and the need to maintain a working speed of 6-8 km/h require a suitably strong draft horse. Depending on the conditions in a given field, 30-40 HP is needed for one tooth. Taking into account the spacing of the tines, i.e. the working width of the subsoiler, we come to the conclusion that only 4-5 tines cover the entire width of the tractor, so in order not to drive "on overlap", a minimum of 120 HP is needed on lighter soil, flat terrain and a relatively small working depth, up to even over 200 HP. With weaker tractors, the laboriousness of the procedure will be enormous, and at the same time, the soil will be further compacted by numerous passes.
