; and (F) an appropriate list of conservation reserve program conservation practice standards, including any modifications to the practice standards, that are appropriate to meeting the State and nationally significant conservation concerns described under subparagraph (A), as determined by the Secretary. (3) Effect on existing agreements (A) In general Subject to subparagraph (B), an agreement under this subsection shall not affect, modify, or interfere with existing agreements under this subchapter. (B) Modification of existing agreements To implement this section, the signatories to an agreement under this subsection may mutually agree to a modification of an agreement entered into before the date of enactment of this section under the Conservation Reserve Enhancement Program established by the Secretary under this subchapter. (c) Payments (1) Matching requirement Any matching requirement under a program shall be satisfied by cash funding or in-kind contributions. (2) Marginal pastureland cost-share payments The Secretary shall ensure that cost-share payments to an owner or operator to install stream fencing, crossings, and alternative water development on marginal pastureland under a program reflect the fair market value of the cost of installation. (3) Cost-share and practice incentive payments On request of an owner or operator, the Secretary shall provide cost-share and practice incentive payments when a major conservation practice component is completed under a program, as determined by the Secretary. (4) Forested riparian buffer maintenance payments (A) In general In the case of an agreement under subsection (b)(1) that includes forested riparian buffers as an eligible conservation practice, the Secretary shall make cost-share payments to encourage the regular management of the forested riparian buffer throughout the term of the agreement, consistent with the conservation plan that covers the eligible land. (B) Limitation The amount of payments received by an owner or operator under subparagraph (A)