20 C.F.R. § 404.1017 – Sharefarmers.

(a) If you are a sharefarmer, your services are not covered as employment, but as self-employment.
(b) You are a sharefarmer if you have an arrangement with the owner or tenant of the land and the arrangement provides for all of the following:
1. (1) You will produce agricultural or horticultural commodities on the land.
2. (2) The commodities you produce or the income from their sale will be divided between you and the person with whom you have the agreement.
3. (3) The amount of your share depends on the amount of commodities you produce.
(c) If under your agreement you are to receive a specific rate of pay, a fixed sum of money or a specific amount of the commodities not based on your production, you are not a sharefarmer for social security purposes.