Final answer:
Corn cultivation covers a significant portion of US land according to USDA data, with maps indicating 10,000 and 2,000 acres per point for grain and silage respectively, and a dramatic increase in corn production observed in North Dakota since 1972. However, the exact percentage of US land covered is not provided, and the expansive use of corn for applications like ethanol production is limited by arable land availability.
Step-by-step explanation:
The percentage of the US land base that is covered with corn is significant, reflecting both the vast areas of land dedicated to its cultivation and the importance of corn in the agricultural economy.
Evaluating data from the US Department of Agriculture (USDA), we find that in 2012, the amount of land used for grain corn harvest was visually depicted with each point on a map representing 10,000 acres, and for corn silage, 2,000 acres per point.
Moreover, North Dakota saw a near tenfold increase in corn production since 1972, demonstrating the shifting agricultural patterns in response to policy and market forces. The discussion in the film Food Inc. likely touches upon these aspects to illustrate how policies have impacted land utilization.
To put it in perspective, as of mid-2019, there has been a considerable increase in land allocated to corn in North Dakota.
While the exact percentage of US land covered by corn is not specified, it's important to note that the USDA estimated that about 4 x 10¹¹ m² of land in the U.S. is used for corn production, which is substantial but still falls short of what would be needed if corn ethanol were to replace the country's oil consumption.
This suggests that while corn covers a notable portion of US land, its expansion for purposes such as providing biofuels like ethanol faces practical and environmental limits.