Security interests in growing and unharvested crops are prohibited, and any security agreement purporting to create a security interest therein is void. The provisions of this section do not apply to any security interest or lien in favor of the United States, this state, any county, or any department or agency of any of them, including the Bank of North Dakota, nor to any financial institution as defined by section 6-01-02 or 21-04-01, nor to any agricultural cooperative or agricultural lending agency, nor to any security interest created by contract to secure money advanced or loaned for the purpose of paying government crop insurance premiums or to secure the purchase price or the rental or improvement of the land upon which the crops covered by the contract are to be grown.