What is the amount of zakat due on crops that are irrigated sometimes by machinery and sometimes by river water, due to water scarcity?

If the crop is irrigated for half the period without cost and for the other half with cost, then three-quarters of the tenth is due on it, by consensus. However, if it is irrigated by one method more than the other, the predominant method is considered, and its ruling overrides the lesser. If the amount of irrigation is unknown, then the entire tenth must be given out to prioritize the right of the poor.