for the poor. By 2000, the food stamp program was the largest component of the farm bill. In 2010, the Tea Party movement brought in many Republicans committed to cutting all federal subsidies, including those agriculture. Meanwhile, urban Democrats strongly opposed reductions, pointing to the severe hardships caused by the 2008–10 economic recession. Though the Agricultural Act of 2014 saw many rural Republican Congressman voting against the program, it passed with bipartisan support. Changing technology Ammonia from plants built during World War II to make explosives became available for making fertilizers, leading to a permanent decline in real fertilizer prices and expanded use. The early 1950s was the peak period for tractor sales in the U.S. as the few remaining mules and work horses were sold for dog food. The horsepower of farm machinery underwent a large expansion. A successful cotton picking machine was introduced in 1949. The machine could do the work of 50 men picking by hand. The great majority of unskilled farm laborers move to urban areas. Research on plant breeding produced varieties of grain crops that could produce high yields with heavy fertilizer input. This resulted in the Green revolution, beginning in the 1940s. By 2000 yields of corn (maize) had risen by a factor of over four. Wheat and soybean yields also rose significantly. Economics and labor After 1945, a continued annual 2% increase in productivity (as opposed to 1% from 1835–1935) led to further increases in farm size and corresponding reductions in the number of farms. Many farmers sold out and moved to nearby towns and cities. Others switched to part-time operation, supported by off-farm employment. The 1960s and 1970s saw major farm worker strikes including the 1965 Delano grape strike and the 1970 Salad Bowl strike. In 1975, the California Agricultural Labor Relations Act of 1975 was enacted, establishing the right to collective bargaining for farmworkers in California, a first in U.S. history. Individuals with prominent roles in farm worker organizing in this period include Cesar Chavez, Dolores Huerta, Larry Itliong, and Philip Vera Cruz. Chavez mobilized California workers into the United Farm Workers organization. In 1990, undocumented workers made up an estimated 14 percent of the farm workforce. By the year 2000, the percentage had grown to over 50%, and has remained around 50% in the 2000-2020 period. In 2015, grain farmers started taking "an extreme step, one not widely seen since