It appears you need to add box 1 and box 3 together, then enter the total in TurboTax (schedule F, 1099-PATR) if the products you buy from the co-op are used in your farm business.
This (Per-Unit Retain Certificates) information below is from IRS pub. 225, page 14. I have attach a link for your reference.
https://www.irs.gov/pub/irs-pdf/p225.pdf
Per-Unit Retain Certificates
A perunit retain certificate is any written notice that shows the stated dollar amount of a perunit retain allocation made to you by the cooperative. A perunit retain allocation is an amount paid to patrons for products sold for them that is fixed without regard to the net earnings of the cooperative. These allocations can be paid in money, other property, or qualified certificates.
Perunit retain certificates issued by a cooperative generally receive the same tax treatment as patronage dividends, discussed earlier.
Qualified certificates. Qualified perunit retain certificates are those issued to patrons who have agreed to include the stated dollar amount of these certificates in income in the year of receipt. The agreement may be made in writing or by getting or keeping membership in a coopera
tive whose bylaws or charter states that membership constitutes agreement. If you receive qualified perunit retain certificates, include the stated dollar amount of the certificates in income on Schedule F, lines 3a and 3b, for the tax year you receive them.
Nonqualified certificates. Do not include the stated dollar value of a nonqualified perunit retain certificate in income when you receive it. Your basis in the certificate is zero. You must include in income any amount you receive from its sale, redemption, or other disposition. Report the amount you receive from the disposition as ordinary income on Schedule F, lines 3a and 3b, for the tax year of disposition
