Iowa Code § 200.12: False or misleading statements.

A commercial fertilizer or beneficial substance is misbranded if it does not identify items promoting plant growth, or if it carries any false or misleading statement upon or attached to the container or stated on the invoice or delivery ticket, or if the container or on the invoice or delivery ticket or in any advertising matter whatsoever connected with, accompanying, or associated with the commercial fertilizer or beneficial substance. Further, the burden of proof of the desirable effect of the commercial fertilizer or beneficial substance on plant growth shall be the responsibility of the registrant.