Is an agreement valid where the share of produce varies annually for a fixed term?

Primary text

An agreement regarding a vineyard or land for three years, where the share for the cultivator is specified as one-half in the first year, one-third in the second, and one-fourth in the third, is valid. This is because the specific share in each year is determinate and known, which validates the contract, similar to stipulating a known amount from each type of produce.