I have never seen in Holland to rotate the fields between crops....

Sowing Tagetes is a good biological way to reduce the nematodes, but you
cannot eliminate them. You have to keep Tagetes on the field for at least 2
months, the longer the better. It is used mainly for the control of
Meloidogyne. The eggs will open if the Tagetes roots get near to them. The
invasional larvae (J2 - juveline nematodes) will enter the roots at their
tips, but this plant is not their host, so they will die within days. If
ther in nothing in the soil, the eggs wil lay there waiting for a host
plant's root for years.