The downwash of a helicopter is principally dependent on the disk loading though some other factors do effect it.
The induced (ideal) downwash for a hovering R22 @ MGW would be 1445 fpm - in practice it would be a little higher.
For a Jet Ranger hovering @ MGW the ideal downwash would be 1711 fpm - again a little higher in practice.
What you really need for this application is a V22! 4500fpm! Or would that just blow a hole in the muddy ground? Mind, it would save them having to dig the foundations or pick the fruit!!!
CRAN