Final answer:
James Oliver's chilled plow was the key technological innovation that allowed homesteaders to effectively turn the soil on the Great Plains, leading to improved farm production.
Step-by-step explanation:
The technological innovation that allowed homesteaders to turn the soil on the Great Plains was advanced farm machinery, specifically improvements made to the plow. While John Deere marketed a steel-faced plow as early as 1838, it was James Oliver's chilled plow in the late 1860s that made a substantial difference to the homesteaders.
This new, cost-effective plow was particularly well-suited for cutting through the shallow grass roots characteristic of the Midwestern terrain and was durable enough to resist damage from rocks just below the surface. This innovation, along with other advancements like hay mowers, manure spreaders, and threshing machines, significantly improved farm production for those who could afford them.