Cover crops have been shown to have considerable benefits – but how do they work in a rotation with sunflowers? “We have observed a number of benefits from cover crops,” says Matthieu Abella, sunflower expert at the Terres Inovia Institute. “These include reduced nitrogen loss in winter, reduced risk of erosion, improved nitrogen mineralisation, carbon storage, and better soil structure.” Plant cover also makes it possible to meet regulatory constraints imposed in vulnerable areas. And within a cereal rotation, they have another interesting effect: They reduce the grass weed burden, particularly Timothy and ryegrass.
Good mixtures
Aside from the agronomic benefits, what impact do cover crops have on yields? “Mixes with leguminous and non-leguminous species maximise the benefits of cover crops, especially in soils with low nitrogen supplies,” says Matthieu. For example, a phacelia / field bean mix is particularly well-suited to use before sunflowers.



Phacelia and field beans are well-suited to growing before sunflowers. Phacelia and mustard scavenge mineral nitrogen well. ©adobestock/zhikun sun, ©adobestock/Amalia Gruber, ©adobestock/Volodymyr
“Cover crops should include species that establish quickly and have a high nitrogen uptake capacity at the end of August / early September – like white mustard or phacelia.” However, growers should avoid niger, flax and buckwheat, which increase the risk of mildew, verticillium wilt, and regrowth, respectively.
Anti-erosion
Long-term effects also need to be taken into account, including the reduced risk of erosion. The clay-limestone slopes of the Lauragais region, south of Toulouse, are highly susceptible to run-off. Cover crops tested in this area were planted at the end of the summer, before sunflowers were sown the following spring.

After a storm seen in May, the soil was held in place where cover crops were used. “Not many soil deposits were observed at the bottom of the slope,” says Matthieu Loos, a Terres Inovia engineer. “On the other hand, at the lower end of the field where sunflowers were sown alone, erosion and soil deposits were observed. However, if the cover crops are sown during the period between crops, it’s important not to compromise sunflower establishment as it will impact yield.”
Plant cover is no substitute for tillage where it is necessary for successful crop and root establishment. In southern areas, the choice of species is similar to that made in the central-western area: Legume-based plant cover to manage the period between crops. But here, the important thing is timing their termination correctly. “You need to intervene about two months before sowing the sunflowers to avoid compromising the crop,” says Matthieu Loos.
Intra-crop cover
Michael Geloen, an engineer at Terres Inovia, explains: “We tested three leguminous species sown with the sunflowers: White clover, lucerne and trefoil.” On average, combining these species with sunflowers reduced crop height by 10-20cm, while flower head diameters remained the same, at 17-19cm. However, the sunflower yield was 25-37% lower.
We have observed a number of benefits from cover crops.
Matthieu Abella
In practice, late sowing of leguminous plants can avoid strong competition with sunflower establishment. However, this technique remains risky as leguminous plants do not always succeed in emerging, as three years of trials have shown. Tests are continuing to evaluate this technique and its benefits for soil structure and nutrition.