W. Va. Code § 19-15-8: Commercial value.

For the purpose of determining the commercial values to be applied under the provisions of section seven of this article, the commissioner shall determine and publish annually the values per unit of nitrogen, available phosphate and soluble potash in fertilizers in this state. The commissioner shall determine from the registrant's sales invoice the values charged for the soil amending ingredients. If no invoice is available or if the invoice fails to provide sufficient information the commissioner may use other methods to determine values. The value so determined and published shall be used in determining and assessing penalty payments.