Who will win in Estonia: climate change or plant breeding? Increase of temperature sum by up to 30 % during the last 20 years
Rene Brand
Internationaler Produktmanager Winterraps - Dipl. Agr. Ing. - innovativ - neugierig
The Estonian rapeseed production faced major challenges during the last 20 years. While winter rapeseed (WOSR) was 20 years ago just a small niche crop, far behind spring rapeseed (SOSR) and only used by a few pioneers, it outperforms spring rapeseed during the last 10 years. Mainly because of innovative plant breeding and new adapted hybrids for Estonian growing conditions.
But since 2020 our rapeseed yield dropped down with a new negative record of just 1,4 t/ha in 2024. Are we able to make the necessary turnaround and why is climate change a crucial reason for this development?
The historical database by Eurostat shows that rapeseed grew only on 50.000 ha, including just 2.000 ha WOSR, 20 years ago. That was just 3,4 % from the acreage of winter crops and underline the status as a new “out of the box” crop for Estonian farmers[1], due to strong winter, lack of winterhardy varieties and less experience.
Till 2010 WOSR grew up in Estonia to 12.300 ha respectively 13 % of the total rapeseed acreage. This development continues with further successful launches of new hybrids like MERCEDES or ATORA. Especially between 2015 and 2020 WOSR could make a visible step forward in the yield performance within average 0,9 t/ha more yield than SOSR (except 2016 and 2018, where we had winter killing and drought). During this period the market changed significantly from 50:50 between both crops to more than 80 % market share for WOSR in 2020.
But the market faced further challenges next to abiotic stress factors like winter killing or drought/heat periods. Since we get more and more limits in our plant protection applications rapeseed crop management becomes more difficult. The loss of the insecticide seed treatment with systemic Neonicotinoids was already a big setback. But especially the last years showed that the limited options for controlling spring weevils are becoming more crucial for a satisfying yield result.
But it remains the question, what can we do? I remember well on an intensive field visit in Estonia this summer, where a young farmer and I discussed all these issues and checked the final pod package of his rapeseed at the same time. The impulse raised up, when we cannot change the official rules of insecticide treatments in spring, it’s worth searching for an advanced yield potential before winter.
Why? Because 70-80 % of the rapeseed yield is made before winter![2]
Winter rapeseed passes several stages before winter, which are crucial for its further yield potential in spring. Next to the golden rule of 8-8-8, which means the plant has to reach 8 leaves, a root neck diameter of at least 8 mm and a tap root of at least 8 cm before winter, we have to look also at the physiological development stages of rapeseed.
The seedling needs after sowing around 4-10 days and 150 °C (degree days, respectively the sum of the average daily temperature) for reaching the cotyledon stage with the first early leaves (BBCH 10).
In the following weeks the young rapeseed plant will develop further leaf pairs, which require between 120-150 °C per leaf pair, depending on daylength, light-intensity and variety. With reaching BBCH 16 (around 550 – 600°C) rapeseed starts with the bud and root differentiation, which means setup of the future pod package respectively yield potential. This phase continues till the plants reached 1.200 °C. Depending on the local winter, this was in the past, usually in March or April.
After finishing the bud and root differentiation, rapeseed continues with the stem elongation phase, where weak buds and lower side branches are reduced. Usually, we prevent this natural mechanism by sufficient nitrogen fertilization.
But what happens if this process is disturbed by climate change respectively increased temperatures in autumn? We observe during the last years an increasing tendency for bigger biomass in autumn, vigorous growth and plants with early stem elongation. All these symptoms based on early sowing dates, higher temperatures and vigorous hybrids. But what are the consequences?
If the young rapeseed plants finished the bud and root differentiation before winter and started already with stem elongation respectively reduction phase, then we are not able to compensate this with our Nitrogen fertilization. Also, we have to keep in mind that these plants usually uptake already the majority of the available Nitrogen from the soil. In consequence they start to suffer and reduce the side branches even more strongly, which means for us an even weaker pod package for the next spring.
The climatic change during the last 20 years will be even more visible if we compare our current autumn conditions with the situation 20 years ago. The article from 2007 about “Sowing date influence on winter oilseed rape overwintering in Estonia” investigate the impact of different sowing dates on the overwintering performance of 2 varieties (EXPRESS and WOTAN)[3]. Peeter L??niste et al. collect also the temperature data for the analyzed growing seasons 2001-02, 2002-03, 2003-04 and 2004-05, which you can see in the picture below (Pic.1).
The temperature figures are measured as GDD (growing-degree-days). As explanation is mentioned in the article: Air temperature data were used to compute the growing-degree-days (GDD) from sowing to wintering in autumn, in all years for each sowing date and cultivar combination. Daily growing-degree-days (DGDD) were calculated using base temperature (BT) of 5 °C and the formula DGDD=mdat-BT, where mdat is the mean daily air temperature (°C). DGDD values were summed from sowing to wintering in autumn for each sowing date-cultivar combination to obtain GDD.
To enable an easy comparison, the temperature figures from today are adapted according to the above-mentioned GDD formula.
The table below (Tab. 1) shows the average temperature sums depending on the different sowing dates. The figures underline a wide range from 273 °C for sowing at the end of August to more than 500 °C for sowing at 08th of August. If we compare this data with current data from 2 locations in Estonia: Erwita (north from J?geva) and Kuusiku (45min south from Tallinn, Pic. 2), then we can recognize[4]:
1.??? We have between 17 – 35 % more temperature accumulated (vs. 2001-2004)
2.??? We had on average almost 2 weeks more vegetation
3.??? Today we are realizing higher temperature sums in comparison to 2001-2004 with even one week later sowing dates
Tab. 1: Comparison of temperature sums from Peeter L??niste et al. (2007) with current temperatures from autumn 2024
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Left: late sowing at 26th of August, reached 398 GDD
Right: early sowing at 15th of August, reached? 532 GDD
While we are searching today for less temperature accumulation before winter to get less stem elongation, prevent an early reduction phase respectively to get an advanced pod package in spring, Peeter L??niste et al. searched 20 years ago for the best overwintering performance.
According to the four sowing dates they have checked, the overwintering performance was between 0 % for late sowing in 2002 and 88 % for the early sowing in the same year. The picture below (Pic. 3) shows the impact from the different sowing dates on the overwintering performance during the tested period 2001-2005.
A summary of the overwintering performance (Tab. 2) underlines that the second date, 15th of August, “guarantee” with 70 % the best result 20 years ago. But table 1 showed clearly how important are adapted sowing dates for our current growing respectively climate conditions. While 20 years ago 15th of August was the best sowing date, we should rethink this especially among the current warm autumn seasons and sow our modern hybrids 5-7 days later.
Tab. 2: Overwintering of the several sowing dates per year
Summary
Peeter L??niste et al. mentioned already in their article from 2007, that early sowing dates (8th of August) are not suitable for a successful rapeseed production in Estonia, due to higher tendency of overgrown rapeseed plants and elongation of the root collar. In contrast they underline that sowing dates later than 20th of August are risky, as the plants will not develop more than 3-4 leaves before winter.
The comparison with actual temperature figures from autumn 2024 underlined that we have today higher temperature sums of 17-35 %. In combination with more vigorous hybrids, we can realize the same physiological development even with a 7 day later sowing.
Our new technical trials in Kuusiku with different sowing dates will confirm, if our modern rapeseed hybrids with temperature sums of more than 500 GDD respectively less than 400 GDD will also struggling by the Estonian winter, as it was summarized in the article from Peeter L??niste et al. in 2007.
[1] Source: Eurostat, https://ec.europa.eu/eurostat/web/agriculture/data/database
[4] Source: temperature data supplied by METK Kuusiku and Linas Agro Estonia
Product Manager
1 个月Anu Ruut
Thank you for summarizing our changes and problems in Estonia with winter rapeseed. This is really good reading and every Estonian farmer should read it. I propose that you share this article with P?llumajandus.ee ??