Heavy rains have crusted the soil, possible overseeding of rapeseed

Ulewy zaskorupiły glebę, możliwe przesiewanie rzepaku

Heavy rainfall in many places could have "sealed" the soil.
Rapeseed is very susceptible to crusting right after sowing. In extreme cases, emergence may not only be thinned out, but even completely stopped.

Rapeseed is very sensitive to soil crusting

The first seeders have barely appeared in the fields, and it is already known that part of the rapeseed plantations will probably have to be sifted. After heavy local rainfall, which on the night from Sunday to Monday moved from the west to the east of the country (as well as on Monday, especially in the first part of the day), many fields are flooded, and water pools have appeared.

There are locations where rainfall exceeded 100 mm/m2. In Lower Silesia, rainfall often approached 120 mm. However, reports from many regions indicate rainfall of 50-60 mm on Sunday night and Monday by noon. Where it rained only at night, rain gauges and weather stations still indicated over 30 mm. All these results are so large that in the case of rapeseed that has already been sown, there is a very high probability that it may not emerge.

This is a problem that occurs every year. Almost every season, during the rape sowing period and immediately after, there is locally heavy rainfall. Meanwhile, rape is very sensitive to heavy rainfall immediately after sowing. It has a much more difficult task than, for example, cereals after sowing, which break through the soil more easily even after heavy rainfall (although even here, emergence may be thinned out if the soil is heavily compacted by rainfall immediately after sowing).

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Will it be necessary to sift rapeseed?

In the case of exceptionally heavy rainfall, not only does the soil compact. Namely, grooves are also created on the surface of the earth, and rapeseed seeds are simply washed away by the stream of water. While the soil is most crusted where it was previously exceptionally dry, heavy rainfall causes the seeds to be washed away even in those places where the humidity during and after sowing was very good.

How much can such heavy rain prevent rapeseed from germinating? In practice, it will be most difficult on plantations that were sown just before the rain. It has often happened that plantations established 1-3 days before the downpour were severely thinned out, and those sown 4-5 days before the rains coped with germination much better. However, there is no rule here. If the plants do not have time to break through the soil, a situation occurs when they bend in contact with the soil surface, which creates a very strong barrier. The layer of crusted soil resembles concrete, which the fragile plant is unable to break through. The worst is if after heavy rains there is a higher temperature and high sunlight, which additionally "hardens" the surface.

It would be best if the storm were followed by some light rain, which could loosen the soil a bit, but even this does not guarantee that the situation will improve.

Will it be necessary to sift plantations that have already been established? We will not be able to say this for sure without observation. In regions where rainfall totals (and at the same time their intensity) were the highest, such a probability is very high. Due to the fact that we are only entering the third decade of August, there will be time for possible sifting. Unfortunately, this involves additional costs. If the stocking density after sowing is very low, then there is not much point in maintaining such a plantation. However, we need to observe the development of events. It may also be the case that the stocking density will be optimal, but the emergence will be very uneven. The plants will emerge in stages. However, if the stocking density is low, e.g. below 20 plants / sq m, then sometimes it is better to sift the plantation. Here, we must count on additional losses (e.g. after winter). And although it has already happened that with good weather conditions, even such rare plantations yielded well, this is roulette. Especially since we are talking about low stocking density at the start of the plantation.

How deep should rapeseed be sown?

Weed infestation must be controlled

Here, attention should also be paid to the issue of herbicides. As a result of heavy rainfall, in many cases they could have been moved deeper into the soil profile. In such a situation, even if the rapeseed stock after emergence is optimal, the plantation must be monitored for weed infestation. It may turn out that a herbicide correction will be necessary. Some of the active substances administered did not remain in the place of action, i.e. at the depth at which weeds germinate. This means that the dose will be too low to combat these plants. In many cases, herbicides could have been washed to such a depth at which their action is pointless. What is more, the phytotoxic effect may also be increased, because the concentration of the substance may be excessive in some points of the field (while in other substances there will be too little for it to work effectively). Any substance can be phytotoxic, although it is worth paying special attention to clomazone (plant discoloration) and metazachlor, which will initially inhibit plant development in the event of accumulation in a given part of the field.