Tillage - false nostalgia or necessity?
The climate change is presenting agriculture with more and more challenges. As a result, the system of intensive tillage and seeding is increasingly questioned.
The climate change no longer is an unremarkable phenomenon, it strikes hard. We witness rainy springs, hot summers, wet autumns and mild winters. However, high annual rainfall does not necessarily mean sufficient water for the crops. A medium-heavy soil can store up to 180 l/m², but a vigorous crop needs 4-6 l/m² per day. Therefore, new water has to be supplied after three to four weeks at the latest, otherwise the plants will reduce their yield. Replenishing can take place in the form of rain, dew or the development of deeper soil layers.
In a dry period, the capillary action is the most important mechanism for achieving acceptable emergence. While in rainy conditions the water required for germination comes from above and the seeds can germinate even if they were sown shallowly, if the soil is dry and/or there is no rainfall after seeding, the germination water must come from the surrounding soil resp. if necessary, from the subsoil. Due to their greater hydrophobia, oleiferous, rank seeds require higher quantities of water compared to starchy seeds. If the contact of the seed to the surrounding soil is not sufficient or if the capillary action is disturbed, e.g. by tillage below the seeding horizon, germination will not be initiated.
But not only just that. During dry periods, capillary forces also transport mobile nutrients such as calcium, nitrate, sulphate, boron etc. back upwards into the root zone. If this transport is disturbed by compaction or a pan, not only the water transport but also the nutrient transport stagnates. A good soil structure therefore does not only ensure root penetration, but also protects the crops from starvation and thirst during dry periods. Large worms in particular create downright drainage systems with its large vertical tubes as it prefers to get its food from the soil surface and pull it into its deeper tubes.
If the expected rainfall arrives, it is essential to ensure that the valuable water remains on the surface. Erosion and stagnant water are reduced if the soil/mulch cover is good. Good infiltration capacity also plays an important role with regard to storing water. This is stable in intact soils without disturbance and compaction zones and develops better in deeper layers the longer the soil has not been moved and has largely developed naturally via biotic engineering (rooting) and biological activity.
Large worms in particular create downright drainage systems with its large vertical tubes as it prefers to get its food from the soil surface and pull it into its deeper tubes.
The role of tillage
In certain situations, tillage is essential to keep yields acceptably high. If for example many tracks were left behind during the harvest or in case of problems with poorly distributed straw/organic material and consequently poor seed embedding and increasing pathogens.
Reduced tillage also increases the pressure caused by mice and slugs. The milder the climate and the lower the precipitations in winter, the more explosive the reproduction and thus the damage can be. To counteract this, you can choose between tillage and chemical measures. The same decision has to be taken if weeds/grasses that are difficult or impossible to control have to be eliminated. Increasing resistance and the discontinuation of certain active agents aggravate this problem.
Sandy soils that are prone to compaction also have to be loosened. Natural loosening by the roots of crops and catch crops usually is not sufficient because of the lower yield potential of these sites.
In principle, with reduced tillage, it is the task of catch crops (at all sites) to stabilise the soil in the period between the crops. If the temporal and spatial gaps without vegetation are too large, the yield of the following crop will decrease.
But even good catch crop populations can lead to a yield reduction of the following crop. In areas with low winter precipitations and often early summer drought, the over-wintering catch crop “steals” too much water. In this case, you need to keep an eye on the water consumption of the catch crop. The problem of water scarcity can also occur if the soil is cultivated deeper before a crop, for example during soil repair measures. However, if, for example, a plough pan is broken up by tillage, this is still positive as the plants afterwards have access to more usable soil volume. The depth of the compaction layer determines the tillage depth.
In addition, the objective of tillage is to mix organic material into the soil to encourage micro bacterial decomposition. In this case, the cultivation depth depends on the activity of the soil. An air-permeable soil can also convert straw that is mixed into deeper layers, whereas heavy, clay soils preserve rather than convert the straw or organic material because of the reducing conditions (without oxygen) at this depth. For an even microbial conversion, an incorporation depth of 2 cm per tonne of straw per hectare is recommended. On heavy soils and in a continental climate, however, a somewhat shallower cultivation may also be reasonable. As a general rule: the evener the incorporation, the evener the subsequent nutrient flow.
When planning a tillage measure, however, we should also be aware, as mentioned above, that every tillage pass costs water. With deep tillage and very poor consolidation without soil mulch, this can amount to up to 40 l/m². The disturbance layers created by incorrect tillage are also critical. For example, a serious plough pan at a depth of 30 cm quickly reduces the water use potential of 180 mm/m² to 40 mm/m² of actual water reservoir. Common crops that root 1.5 m to 2 m deep - assuming the soil type allows for this depth - can then no longer fully develop the actually usable part with their roots.
In addition, tillage disturbs the capillary action which is essential in dry periods. In this case, the focus has to be on an optimum seed embedding during seeding and on consolidation during tillage. The connection to the soil capillary is achieved by a finely crumbled seedbed, by adjusting the pressure of the closing wheels at the seed drill and/or by rolling after seeding.
Optimum consolidation can only be achieved with heavy packers if the soil is sufficiently moist. Because of the lack of "adhesive moisture", dry soil consolidates naturally only with sufficient time which often is scarce.
Especially the last point shows that in some cases less tillage can be more. The point which you are at in the crop rotation plays a minor role. To better compensate changing environmental conditions, direct seeding is becoming increasingly justified as part of our cultivation system. However, direct seeding never is an acute problem solver. On the contrary: it requires good arable conditions and, as described above, is more restricted by higher requirements of the site than other tillage systems.
But why draw a strict line between tillage and direct seeding when hybrid approaches, such as StripTill, rotative direct seeding and the offset method, are alternatives and combine the advantages of both systems?
Comparison of hybrid approaches
The term "rotative direct seeding" describes the alternating cultivation within the rotation. Cereals can usually be established after taproot crops such as rapeseed or soya without deep tillage. Additional interventions tend to rather destroy the natural soil structure and unnecessarily consume energy and time. In Central European conditions, for example, the diesel consumption of direct seeding is only just under 1/3 of the consumption of inversion tillage per hectare and year.
StripTill as a combined method provides a solution for narrow time windows and is usually used when the crops can benefit from an additional deep loosening also from an economic point of view or can utilise the faster warming due to the loosening in an extended vegetation period. In this respect, rapeseed and maize are the typical crops. While StripTill for maize does not always produce higher yields, with rapeseed it offers the possibility of luring the taproot downwards with concentrated fertiliser depots.
Offset methods are ideal if variability is required. Primary soil cultivation and the creation of fertiliser depots are separated from seeding in terms of time. Traditional seed drills with only minimal soil intervention are often used for seeding. On problematic sites with black grass, pressure can be reduced with additional shallow cultivation passes. Moreover, the advantage of this separation is that the soil can become denser resp. consolidate naturally over the longer period between tillage and seeding and that capillarity is also established even in late, dry seeding conditions. However, if the seed drill is equipped with front tools, they should maximally be set to the seed depth level.
Coulter technology for the respective seeding method
But which is the optimum tool for the different conditions and circumstances?
In general, a compact, consolidated soil has higher requirements on the seeding technology. Light coulter designs work wonderfully behind power harrows, but do not achieve the coulter pressure required for direct seeding. Heavy seeding units, usually with a wider row spacing and the possibility to apply a lot of coulter pressure section by section, place the seed at the same seed depth even in changing conditions. Tine coulters work best with short-cut organic material. Stones are moved aside, and the capillary action is achieved even in heavy soils. Disc coulters adapt better to uneven ground and move less soil, but have disadvantages with stones and in unfavourable conditions and without front trash wheels they sometimes struggle with hairpinning –the seed in straw residue.
As in extremely dry conditions on heavy soils and deep seed placement, because of a lack of fine soil disc coulters only close the seed furrow if the machine setting is perfect, a preceding, ultra-shallow cultivation pass has become increasingly popular in traditional direct seeding areas. A quick pass with a knife roller or a very shallowly set disc harrow often is sufficient to avoid the drying chimney effect of intact stubble, to level slightly and finally to leave enough fine soil to close the seed furrow.
Summary
With regard to climate changes, the traditional, tried and tested system of intensive tillage followed by seeding has to be questioned. However, the aspect of considering tillage more as a kind of tool, for example to incorporate organic material, mechanically control weeds or carry out soil repair measures, also confirm its right to exist. On the other hand, there still are the advantages of direct seeding and reduced tillage - especially with regard to saving water.
In this case, it helps to stop thinking in black and white. Regarding the changing climatic conditions, for example rotative direct seeding, StripTill and the offset method can be considered as more flexible and adaptable alternatives. Their integration into our rotations is already in full swing in regions characterised by drought (Central Germany), weeds (Western Europe) or moisture (England).
This article was updated on 4 September 2024.