Imposition of tax on byproducts of potash production

A subsurface mineral tax of four percent is imposed upon the gross value of all subsurface mineral byproducts produced during the processing of potash produced within this state. The tax levied attaches to the whole production of byproducts. Inventory is not taxable until it is sold.
The gross value at the processing plant is the price paid for the byproducts under an arm's-length contract between the taxpayer and the purchaser. In the absence of an arm's-length contract, the gross value at the processing plant is established by the price paid under an arm's-length contract, to which the person paying the tax is a party, for the purchase or sale of byproducts of like kind, character, and quality.