A:
There is nothing wrong with a wife working on a farm, as long as she observes Hijab in the presence of foreign men who are non-Mahram (not a spouse or an unmarriageable relative).
However, Zakah is due on the harvest of the farm, if it is of the grains that are stored such as dates, grapes, wheat, barley, etc. The due Zakah is 5% of the produce from land irrigated by machinery and the like, and 10% from land irrigated by rains, rivers, and the like.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.