“Seedbed before seeding time” – a popular saying among farmers. But how much of this sentence is true?
In general, it is important that you do not drive on the soil too early in spring. Any compaction that is caused by doing so is extremely difficult to repair. The farmer would have to carry out deep tillage what is almost impossible in spring. Thus, we usually have to accept compaction in spring. The only way out: be patient and only drive on the soil if has dried sufficiently. Some farmers often find it difficult to have this patience. Soil temperature can help a little bit. For if the soil temperature does not exceed the values given in the chart, plants will not germinate.
1. Low temperatures
In addition to the optimum embedding for a good root growth and the placement depth, there are numerous other requirements the seed makes on sowing. One of them is the soil temperature.
The earlier you sow, the more days the plant has left for vegetation. However, if the soil is too cold and insolation is too low, sowing early does not have any advantages, for the plant simply does not start to grow. As you can see in the chart, it requires a certain minimum soil temperature to start the germination process.
| Crop | Germination temperature in ° C |
| Maize | 8-10 |
| Oats | 3-5 |
| Barley | 2-4 |
| Wheat | 2-4 |
| Sunflowers white | 15 – 25 |
| Sunflowers black | 7 – 8 |
| Soybeans | 10 |
| Sugar beet | 5 |
However, with the seedbed preparation we can influence the temperatures of the upper soil layer to some degree. If we manage to create a loose and fine-crumbly seedbed, the topsoil aerates much faster and thus also heats up faster.
2. Heavily saturated soils
Let’ take a quick look back at the spring of 2023. In addition to the already abundant winter rainfall, there was high and continuing rainfall. If we compare the rainfall in March with the multi-year average, we notice that almost 50% more rain fell for example in Regensburg (DE).
© Deutscher Wetterdienst (DWD)
This, of course, refills the water supply in the soil and is an important buffer for the summer – we already saw this last year. But the wet soils entail some big challenges with regard to sowing in spring:
Beside the optimum seedbed, in wet years the attention also is on the subsoil. Keyword: avoid compaction to not affect gas exchange, root growth and water circuit. Easier said than done. In this case the solution is to wait to avoid structural damages.
Let’s turn to maize, the largest spring crop in Germany and in the same context to organic fertilisation which many farms carry out before sowing. The weight of the efficient application technology exceeds the weight of the sowing technology by far and thus makes even more demands on a good bearing soil.
After the increased rainfall in spring 2023, the soil was to dry off as fast as possible. However, the amount of organic material on the fields was another challenge.
To avoid losing additional valuable vegetation time after this long period of rainfall, a lot of farms schedule an herbicide application to quickly get a grip on catch crops and old weeds.
In the first step, our task will be to aerate the topsoil and to crush the catch crops. Only if the topsoil has dried off a little bit, you can drive on the fields with more heavier machines without risking compactions of the subsoil. During the first pass you should not carry out a surface cultivation to avoid smear horizons. These smear layers affect gas exchange, the water circuit and later even the root growth.
To avoid smear layers, discs are a good choice for the first pass. As the discs only penetrate the soil vertically and break the space between the individual discs, they do not create any smear layer. To avoid additional compaction on the headlands, models that turn on the packer are advantageous.
If there is a lot of organic material on the surface that shades the area and prevents drying off, it may make sense to crush it in advance and encourage the drying effect. As opposed to a mulch tool which requires considerably more fuel and time, the knife roller tears open the soil surface additionally.
Another option is to work downwards step by step with a tine tool. With more passages the soil can aerate better. If you work too deeply at the first time, you take large clods to the surface which will cause problems with regard to the following population management.
Tine tools with narrower points and a tighter tine spacing are clearly at an advantage.
The rougher the structure is after cultivation and the less you consolidate, the more water evaporates and the faster the soil dries off. For sensitive soils with a high clay content, it may be advantageous to cultivate without consolidation. An example is our Finer: for such conditions you can change between packer and support wheels.
After the trafficability has been improved and the catch crops have been crushed, we are back to the traditional seedbed preparation. We already know these requirements from the other two blog articles about seedbed preparation: Seedbed preparation – for an optimum embedding of the seed
To create a fine-crumbly and consolidated seed horizon, seedbed preparation with a tool including a packer is indispensable.
As always, the choice of the right packer depends on the site: What is the crumbling behaviour of my soil, is it prone to tight lodging, is the cohesion low or can it carry loads only to a limited extent? Moreover, the previous cultivation depth is a key criterion when it comes to choosing a packer.
Difficult conditions like this year also bring about bigger challenges. Those who wait too long, give away vegetation time. Those who go into the field too early and in wet conditions, risk compaction and, thus, yield losses. If the right technology is used correctly, one more pass can be the more economic solution. Regardless of the strategy, wide-base tyres with little air pressure have top priority in wet conditions.
(Blogpost: Soil conservation vs. heavy machines (I)).
In addition, light tractors and trailed mounted implements are advantageous.
