Which of the following innovations is associated with John Deere?

The correct answer is associated with John Deere's significant contribution to agriculture through the invention of the steel plow. Deere created the first successful steel plow in 1837, which transformed farming practices, particularly in the Midwestern United States. This innovation was critical because it allowed farmers to effectively cultivate the tough, sticky soil prevalent in that region. The design featured a sharp, curved blade made of steel, which reduced the friction encountered by traditional iron plows. As a result, farmers could plow more efficiently and with less soil sticking to the blade, making the plowing process much easier and faster.

The other innovations listed, while important to agricultural development, are not connected to John Deere. The seed drill, attributed to Jethro Tull, improved the planting process by allowing seeds to be sown in rows at proper depths. The mechanical reaper, invented by Cyrus McCormick, revolutionized the harvesting of crops by mechanizing the cutting process. The iron harrow was an earlier implement used for breaking up and smoothing out the soil but does not carry the historical significance or direct association with Deere's innovations in agriculture as the steel plow does.