Which preposition to use with ditchers

in Occurrences 1%

In addition to their field strength and the children, of whom no reckoning was made in the schedule of employments, the two plantations together had five stable men, two carpenters, a miller and job worker, a keeper of the boat landing, three nurses and two overseers' cooks; and also thirty-five ditchers in the reclamation work.

Which preposition to use with  ditchers