S.D. Codified Laws § 49-45-10

A grain buyer must pay the purchase price to the owner or the owner's agent for grain upon delivery or demand of the owner or agent unless payment is to be made in accordance with the terms of a voluntary credit sale that complies with the requirements of this chapter and rules promulgated thereto. Full payment of any cash purchase must be made by the Class A grain buyer within thirty days of final delivery. A Class B grain buyer must pay for the grain included on a uniform scale ticket or comparable receipt, as defined in § 49-45-10.1, within thirty days of issuance.