URA - Regulatory requirements, found at § 24.103.
USPAP and UASFLA are both secondary, non regulatory resources on URA projects.
UASFLA = Uniform Appraisal Standards for Federal Land Acquisition, published by the Interagency Land Acquisition Conference, chaired and managed by the US Department of Justice. It is fundamentally an appraisal manual for Federal eminent domain appraisal preparation and Federal court testimony. These are appraisal standards utilized by the Department of Justice and other Federal agencies when processing appraisals for direct Federal acquisitions.
UASFLA is primarily relevant to direct Federal projects where the Federal agency has adopted the standard and is undertaking the acquisition directly. UASFLA is not specifically applicable to federally-assisted projects undertaken by state and local agencies. Most states will have their own body of law as to what is compensable in eminent domain and have definitions of "market value" that vary from the Federal ground rules. Additional rules will differ among the states and Federal government on such things as how appraisals are undertaken for partial acquisitions.
The UASFLA may however, provide useful insight to States on issues of compensability and valuations encountered when doing acquisitions under eminent domain. It may be particularly helpful if a state follows the "strict before and after" Federal rule for partial acquisitions. The USASFLA has no legal standing (like the URA and this Regulation do) - It is essentially, a publication of the US Department of Justice.