date means each date on which interest is payable by the issuer under the terms of the bond. . (c) Conforming amendments (1) The table of subparts for part IV of subchapter A of chapter 1 of such Code is amended by adding at the end the following new item: Subpart H. Nonrefundable credit to holders of certain bonds. . (2) The table of sections for subchapter B of chapter 65 of such Code is amended by adding at the end the following new item: Sec. 6431. Credit for qualified renewable energy bonds allowed to issuer. . (3) Section 6211(b)(4)(A) of such Code is amended by striking ‘‘and 36B, 168(k)(4)’’ and inserting 36B, 168(k)(4), and 6431 . (4) Section 6401(b)(1) of such Code is amended by striking ‘‘and G’’ and inserting ‘‘G, and H’’. (d) Effective Date The amendments made by this section shall apply to bonds issued after the date of the enactment of this Act. 5. Study of biogas and nutrient reuse (a) In General The Secretary of the Treasury shall enter into an agreement with the National Renewable Energy Laboratory to undertake a study of biogas that addresses the following: (1) The quality of biogas, including a comparison of biogas to natural gas and the identification of any components of biogas which make biogas unsuitable for injection into existing natural gas pipelines. (2) Methods for obtaining the highest energy content in biogas, including the use of co-digestion and identifying the optimal feed mixture. (3) Recommendations for the expansion of biogas production, including an analysis of the extent to which increasing the methane content of biogas would result in the greater use of biogas and an analysis of how the expanded use of biogas could help meet the growing energy needs of the United States. (4) Methods for productive use of nutrients recovered from qualified manure resource recovery property that benefits the agricultural economy. (b) Report Not later than 2 years after the date of the enactment of this Act, the Secretary shall submit to Congress a report on the study conducted under