1. Compared to 1948 levels of employment, the U.S. agriculture sector has lost more than twice as many jobs (5.83 million) as the manufacturing sector (2.74 million).
2. Compared to their respective peak levels of employment, the agriculture sector has contracted by 72.3% since 1948 (-5.83 million jobs), which is much higher on a percentage basis than the manufacturing sector's percentage contraction of 40.2% (-7.86 million) since the peak employment level of 19.55 million in 1979.
Even though job losses in America's farming sector have been much greater both in absolute numbers since 1948 and in percentage terms from their peak levels, when have you ever heard anybody complain about the "decline of U.S. farming" (only about 400 Google search results, many to this blog) or claim that "America doesn't grow anything any more" (no Google results)? In contrast, you'll find 141,000 Google results for "decline of U.S. manufacturing" and 19,500 Google results for "America doesn't make anything anymore."
The long-term trends are the same in both manufacturing and farming: Technological advances lead to huge increases in worker productivity, which then requires fewer and fewer workers to produce more and more output. The huge gains in productive efficiency and worker productivity lead to significantly lower and more affordable prices for consumers, leading to a reduced share of food and manufactured goods in both household income and national income (GDP), but increasing levels of output in absolute terms. For these long-term trends we should be grateful for their major contribution to our ever-increasing standard of living.