Thank you for your question. Farmers in south Dakota do not require a sales tax certificate to collect sales tax and remit it to the state, if it is for casual sales.
However, if the farmer is holding them out for retail sales of farm priducts to the pubic, that is for example: you have a pick it yourself program where the public is invited on thte property, or you actively advertise, to bring people on to the property, etc, then a sales tax is required.
For your convenience, I am providing you a copy of that specific paragraph from the SD tax laws and regulations:
64:06:03:01. Agricultural products. Gross receipts from sales of farm products by a farmer for resale are not subject to sales tax. If a farmer holds out to the public as a seller of farm products and makes regular sales to consumers, the farmer is in a retail business and must have a sales tax license and report the tax on such sales. A farmer making occasional sales of farm products to consumers is not required to have a sales tax license and report sales tax on the sales.