- It is often said about delayed sowing that it creates a greater risk of yield loss. But when do we talk about delayed sowing?
- What yield losses can we experience with delays? Where is it late in the context of rapeseed sowing?
What is the yield reduction with delayed sowing?
Studies on the cultivation of winter rapeseed quite clearly indicate a decrease in yield due to delayed sowing – or the possibility of such a decrease. But what kind of decrease is this? Does it have to occur? And what's more – when is sowing already delayed?
Some scientific sources speak of a drop in yield of around 100 kg/ha for each day of delay in relation to the optimal sowing date, although only in the event of a severe winter. However, if it were milder, the drop in yield could be around 20 kg/ha for each day of delay. The differences are therefore significant. If we were to adopt this methodology, it may turn out that by sowing rape a week later than the optimal date, we can lose at least 140 kg/ha. On the other hand, if the winter were to take a more severe form, we are talking about a drop of up to 700 kg/ha with a week's delay.
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Late Sowing of Rapeseed. A Mistake or the Right Decision?
When is sowing delayed? Where is the risk greater?
However, we need to start with when can we actually talk about a delayed date? If we were to rely only on the sowing dates set several decades ago, then in principle we would be talking about delayed sowing throughout the country. Let us recall here that the previous dates for the entire country were in force from 5 to 25 August (only in small areas in the southern reaches, including the Kłodzko Valley or the areas around Żywiec and Bielsko Biała, the date was set at 31 August). However, they are out of date. These dates have not been officially changed so far, but so-called sowing by the book is no longer the best solution in many cases. It is increasingly said that a safe postponement of the sowing date is a period of about a week. In such a situation, for example in Podlasie or the south-eastern reaches of Podkarpacie, where the so-called optimal dates were previously set at 5 to 10 August, it would not be a mistake to sow rapeseed by 15 August. At the same time, later we can actually talk about slightly delayed sowing, although as we know very well – sowing in these regions was still ongoing at the end of last week. In the Lublin region, in the eastern part of Mazovia and in the south of Warmia and Mazury, the optimal sowing date according to the current methodology is 11-15 August. Meanwhile, after the shift, we can say that it is safe to sow rapeseed up to 22 August. The central belt from Pomerania through Kujawy, part of the Łódź province, Świętokrzyskie and part of Podkarpacie, according to the current dates, is the period between 16 and 20 August. Meanwhile, up to 25 August we can talk about the optimal date, if we assume that we are shifting the border dates of sowing in the optimal date to a slightly later date. For the rest of the country, 25 August has so far been the point defining the end of the optimal date, however, at the moment the end of August will be closer to the truth.
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How quickly does rapeseed sprout?
So, assuming such dates, it turns out that in western Poland, and above all in the southern part of Wielkopolska, Lubuskie Land, Lower Silesia and Opole Province, as well as in Upper Silesia – we are still talking about optimal dates. In other regions, we can actually already talk about delayed forces, with a greater delay currently affecting the eastern regions, and small delays in the central belt. After all, if we were to continue to follow the official sowing dates in the entire country, sowing would be delayed. However, this is not the case in the western part, for example.
You can sow in September, but not everywhere.
It is said that delaying sowing by a week in relation to the optimal date is not dangerous. And indeed, plantations sown, for example, in the West, even at the beginning of boiling, often did quite well. But here we are talking primarily about sowing dates to date. Additionally, each day of delay is associated with greater dependence on weather conditions, not only winter ones. Although rapeseed needs an appropriate amount of temperatures in the autumn period, let us remember that subsequent September or October days may be increasingly colder. Consequently, the required sum of degree days for the proper development of rapeseed in the autumn will be obtained in a longer period. If vegetation were to be stopped earlier, i.e., for example, the first winter tremors appeared at the end of October, which has already happened, then we have a certain problem. Although this also depends on the earlier course of the weather. In very warm September and October, plantations sown even at a slightly delayed date managed to develop high biomass, an appropriate root collar diameter and a well-built rosette. This was the case last year. But there is little point in taking just one season for granted. Much also depends on what we are actually sowing. Hybrid or population? Hybrid varieties are generally more tolerant of delays in sowing, but they are not able to compensate for large delays.
So the end of August is still a relatively safe date for Lower Silesia, Opole Province, Lubusz Land and southern Wielkopolska. The further east and north you go, the higher the risk of such sowing. If you sow rapeseed, for example, in Podlasie at the end of August, you cannot say that you have a guaranteed loss of yield. However, the risk of a drop in yield is already very high here. So you can assume that if you sow rapeseed later than a week in relation to the previously optimal sowing dates, a drop in yield will be a serious risk. And what could it be? It depends on when winter arrives and how intense it will be. In extreme cases, let's go back to the beginning, researchers of the problem indicate a loss in yield of up to 100 kg/ha for each day of delay.
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