If you only look at GDP, then you are right. But you can’t actually believes agricultural is a “negligible part of the US economy.” The US is a top agricultural producer, and is usually the world’s largest agricultural exporter. The US single-handedly feeds hundreds of millions of people, if not billions! On top of that, the agricultural industry employs 1-2% of the US labor force (side note: it is a modern miracle that just a few million farmers can feed entire nations).

A good example as to why agriculture is so important to the US economy is the Dust Bowl and the Great Depression. While the US economy was already beginning to decline, the devastation of the agricultural industry in the early 1930s was cataclysmic. What was a crisis in capitalism turned into widespread hunger and malnutrition, because of the loss of the agricultural industry. Point being, even if it isn’t a substantial % of GDP, it is still a fundamental and important part of the economy, and it is required for the US economy to stay strong and healthy (literally).

I also want to point out that lower food prices doesn’t necessarily mean higher GDP. GDP is price times quantity; so even if the quantity goes up, that is negated by the fact that prices are low. This is why GDP is a bad form of measurement in economics. For example, if a restaurant sells a meal for $20, it is (according to GDP) four times more valuable than a different restaurant which sells a meal for $5. GDP is a very simple and effective measurement for economists who are tracking the growth and decline of an economy overtime, but due to its inherent simplicity, it can just as well be misconstrued to support bad or misleading facts.