- Rapeseed needs less water in autumn than in spring, but how much exactly?
- When is autumn water demand crucial for rapeseed?
Water is needed right from the start
The soil moisture level currently falls within a fairly wide range nationwide. There are locations where soil conditions are optimal for sowing rape, but on the other hand, many regions are very dry – so dry that good pre-sowing cultivation is out of the question. In such conditions, it is better not to rush into sowing rape, especially since we still have time (unless we are talking about huge areas, when sowing must be accelerated to manage to sow all the fields).
The drought is being exacerbated by the extreme heat in recent days. Meanwhile, every plant needs good moisture conditions at the time of sowing or planting. Rapeseed is no different, of course. The high demand for water is associated with the entire course of vegetation. And how much water does rapeseed need in autumn?
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How deep should rapeseed be sown?
The most important thing is good moisture from sowing to emergence
The good news is that rapeseed needs a minimum amount of water right after sowing. This is due to the small volume of the seed, which will start to swell and germinate even at low moisture levels. However, in significantly dry soil, germination will be disrupted. What is very important, however, is that proper moisture at the sowing stage is crucial for the further development of the plantation. With a lack of moisture, germination is very uneven, which leads directly to problems with the proper management of the plantation in autumn. It is then difficult to precisely determine the date of a possible post-emergence herbicide treatment, autumn regulation of the crop is also difficult, and plants are exposed to pest attack in an even wider time frame. So, despite the low water requirement for germination, let's pay attention to the moisture in the soil. Otherwise, we create problems with the management of the plantation right from the start.
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How much rapeseed to sow per hectare? How to calculate the seeding rate?
In autumn, rapeseed has much lower water demand than in spring.
Generally, moisture at the time of sowing – and in fact from sowing to emergence – is in a sense more important than later. Although water is of course also necessary later on, it is at the start that we are going to be able to manage the plantation.
Rapeseed shows medium sensitivity to autumn water shortages. This does not mean that it is tolerant of them. Nevertheless, rapeseed shows much higher sensitivity to water shortages in the spring.
It is estimated that rapeseed during vegetation has a total water requirement of around 600-700 mm of water/m2. However, in autumn it will take up 10-20% of the total requirement. In total, during autumn vegetation, rapeseed will need around 70-120 mm of water per meter.
Of course, while moisture is key from sowing to emergence, providing it during leaf development will also be very important. Rapeseed without the right amount of water will develop more slowly, and the plants will be weak. While the development of subsequent leaves is often discussed in the context of the sum of temperatures, without water, the plants will not be able to produce the right amount of leaves, and as a result, there will be a loss in yield at this stage. This is directly related to poorer preparation for wintering, because without good moisture, the use of nutrients supplied before sowing will be poor (not to mention any additional top dressing).
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