Maybe I'm missing something really important here but did we really need a study to prove the railroads made agriculture boom?
During the 1850s, land in U.S. farms surged by more than 100 million acres while almost 50 million acres of land were transformed from their raw, natural state into productive farmland. The time and expense of transforming this land into a productive resource represented a significant fraction of domestic capital formation at the time and was an important contributor to American economic growth. Even more impressive, however, was the fact that almost half of these total net additions to cropland occurred in just seven Midwestern states which comprised barely less than one-eighth of the land area of the country at that time. Using a new GIS-based transportation database linked to county-level census, we estimate that at least a quarter (and possibly two-thirds or more) of this increase can be linked directly to the coming of the railroad to the region. Farmers responded to the shrinking transportation wedge and rising revenue productivity by rapidly expanding the area under cultivation and these changes, in turn, drove rising farm and land values. [More]
In fairness, I did not plunk down $5 for the paper on principle, but just looking at the age of towns in IL for one example, the ones on the IL Central tend to be the oldest. The railroads also prompted the immigration of millions of Northern Europeans to the Midwest and forever altered its previously Yankee culture.
That influence was by far the more important for America, IMHO.