Technological change in agriculture during the period from 1865-1900 was not that dramatic, but some of the changes around agriculture were very significant. The development of the railroad was paramount, opening agricultural expansion in the western states and allowing easier access to markets. The railroads carried livestock to abattoirs and slaughterhouses in cities like Chicago and Cincinnati, leading to dramatic increases in the industrial processing of agricultural goods and the growth of urban areas connected to the Great West.
One technological innovation introduced in 1860s was barbed wire, which spoke to the importance of maintaining control of livestock herds and grazing land, something that was always a challenge in the "wild west." Innovations in chemistry in the mid-1800s led to better methods of fertilization, also increasing yields. There was also some progress in breeding techniques, creating hybrids with more hardiness and yield.
These were some of the developments that led to the increasing mechanization and commercialization of agriculture from 1865-1900, a process that only accelerated in the 20th century.