Agriculture in the WTO: Rules and Limits on U.S. Domestic Support [Updated March 3, 2021] [open pdf - 1MB]
From the Summary: "Omnibus U.S. farm legislation--referred to as the farm bill--has typically been renewed every five or six years. Farm revenue support programs have been a part of U.S. farm bills since the 1930s. Each successive farm bill usually involves some modification or replacement of existing farm programs. A key question likely to be asked of every new farm proposal or program is how it will affect U.S. commitments under the World Trade Organization's (WTO's) Agreement on Agriculture (AoA) and its Agreement on Subsidies and Countervailing Measures (SCM). The United States is currently committed, under the AoA, to spend no more than $19.1 billion annually on those domestic farm support programs most likely to distort trade--referred to as amber box programs and measured by the Aggregate Measure of Support (AMS). The AoA spells out the rules for countries to determine whether their policies--for any given year--are potentially trade distorting and how to calculate the costs."
CRS Report for Congress, R45305
Congressional Research Service: https://crsreports.congress.gov/