Opti­mising rape­seed condi­tions

“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.