Tillage - false nostalgia or necessity? (Part 1)
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.
Relationship between soil cultivation and water and nutrient balance
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.
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 positive and negative effects of tillage on soil structure
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.
The impacts of catch crops & the incorporation of organic material
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.
Water consumption, capillary action and optimum consolidation
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.
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.
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.
Find out how the advantages of tillage and direct seeding can be combined in Tillage - false nostalgia or necessity? (Part 1).
The full article was published in advance exclusively in terraHORSCH issue 28-2024