“The aim of the ‘Secure Rapeseed’ project was to identify the best combination of sowing date, nutrition, and companion plants,” says Alizée Loiseau of Agrosolutions. “We looked at the interaction of these three parameters to determine the cost benefit of four different experimental arrangements.” Even in the first year of the project, 2021, it was clear which options were best.
“The drilling method altered gross margins by €300/ha (£266) – results ranged from €911 to €1,294/ha (£807-£1,147), based on a rapeseed price of €500/t (£443). So it is certainly possible to earn more from rapeseed,” says Ms Loiseau. That is exactly what the project partners; the Noriap Co-operative, which has 8,500 members in the Hauts de France Region, Agrosolutions consultants, and seed company RAGT, want to show.
They compared gross margins for four sowing dates between early August and mid-September. In 2020/2021, August 24 and September 3 gave the best results. However, any choice of sowing date must also take into account the risk of autumn pests, in particular flea beetles.
Sowing before mid-August protects against pest infestations
At the Poix de Picardie trials site, Philippe Pluquet, Agronomic Manager at the Noriap Co-operative, found early sowing optimised yields. “We launched the ‘Secure Rapeseed’ trial platform because farmers were finding it increasingly difficult to get rapeseed to germinate in very dry post-harvest periods,” he says. “We then worked on changing the sowing dates, fertiliser applications, and companion crops.”
Pressure from flea beetles in the autumn has increased, and neonicotinoid insecticides have been banned, so it’s increasingly important to select the ideal sowing dates to ensure the crop is not too immature and susceptible to flea beetle damage in mid to late September. “Everything is in favour of very early sowing, because the later you sow, the more flea beetle larvae will appear in the crop at the end of winter,” says Mr Pluquet. Of course, it is not possible to recommend an exact date, as it depends on the conditions each year, but drilling in the first half of August seems the most favourable.
“We know that if rapeseed has reached the six-leaf stage by September 20, it will do well against adult flea beetles,” he adds. “To achieve this, sowing should be earlier than the common practice of August 25 to September 5. In 2020 and 2021 we trialled sowing on August 7 and 11, respectively, which, followed by rain, led to rapid germination. The crop was then sufficiently developed by September to not require pesticide treatment against adult flea beetles.” Even so, he still recommends using pesticide against flea beetle larvae to prevent them developing by winter’s end.
Another way of sowing early
The Secure Rapeseed method is continually being developed. After harvesting the previous cereal crop, Noriap recommends preparing the soil as quickly as possible and finishing with a roller, so that the field is ready to drill as soon as conditions are right. “This means an organisational change, because you have to start sowing immediately after harvest,” says Mr Pluqet. “It also means securing the seed very early.”
But the Inovia Land Technical Institute agrees with the principle: “We recommend checking your soil structure with a spade test, keeping it as moist as possible before sowing, and using a low seed rate to ensure continuous growth in the autumn,” says Michael Geloen, Terres Inovia development engineer. “Ideally, the rapeseed should exceed four leaves by September 15.” Early tillage also has a positive effect on profitability: At Picardie, the early sown crops yielded 0.39t/ha more than the control plot in 2021.
“Sowing early produces significant biomass, so the crop is ‘hungry’ in the autumn,” says Mr Geloen. It therefore needs a starter fertiliser, although overall dose rates don’t need to increase – just boost the amount of nitrogen used early, at sowing, with reduced rates in the spring. Compared to the control, this increased yields by 0.32t/ha at Picardie. “In the best cases, it is possible to obtain up to 0.7t/ha more than with the unfertilised control,” adds Mr Pluquet. Overall, using starter fertiliser stabilised yields in early sown crops, with or without companion plants.
The companion plant effect
“Companion crops, which are usually legumes, have the advantage of reducing rape’s sensitivity to pests. They also fix about 30 kg/ha of nitrogen into the soil, which is far from negligible,” says Mr Pluquet. “To better assess their effect, we are going to test diversified mixtures of species including clover, fenugreek, vetch and meadow vetchling.”
It is essential to sow the companion plants before the end of August for maximum growth. The best results on the Secure Rapeseed platform were obtained when sowing between August 7 and 24, to make the sowing costs worthwhile. In 2021, the rape drilled with companion crops yielded 0.13t/ha more than the control, but there were also benefits to the subsequent crop. When combined with early sowing and fertiliser, it boosted yields by 0.41t/ha and the gross margin by €128/ha (£113) in 2021, compared to the control, based on a rapeseed price of €500/t (£443) (or €67/ha (£59) with a rapeseed price of €350/t £310)).
Similar results have been recorded in the Champagne Region. Over three years, trials at Syppre show that average yields of rapeseed grown with legumes, lentils and beans were 0.3t/ha higher than when grown alone. If successfully established, as in 2019, input costs were reduced by 16% due to a 21% drop in insecticide and a 24% reduction in fertiliser thanks to the nitrogen fixation. “Sowing rapeseed together with legumes like lentils and fava beans helped maintain yields while reducing nitrogen and pesticide use,” notes Terres Inovia. Early sowing with companion crops could therefore become common practice in the coming seasons.
Field trial results*
+€145 /ha (£129)
gross margin with starter fertiliser
+€50 /ha (£44)
gross margin with companion plants
+€136 /ha (£310)
gross margin with early tillage
* for rapeseed selling at €350/t (£310)