Technology changed US agriculture in many ways during the time period you mention. Two of the most important changes were A) the fact that technology allowed the Great Plains to be settled and farmed and B) the fact that technology led to the creation of bigger and bigger farms and the beginning of a long decline for small farms.
Technology allowed the Great Plains to be opened to agriculture. Perhaps the most important advances were John Deere's steel plow (which made it much easier to break the thick and heavy soil of the area) and barbed wire (which could keep livestock out of fields). The railroads were also very important as they connected farmers to markets.
At the same time, technology favored bigger farms. Much of the technology was either expensive and/or needed large spaces to work effectively (you can't use a huge combine in a small field). Because of this, the new technology made large farms more competitive than small farms. That started the process that brought us to the situation we have now where most farming is done by large agricultural firms rather than by families.