In numbers of educated people employed in it, agriculture in the United States is very small (Look at http://www.census.gov/dataviz/visualizations/stem/stem-html/ . See “Agriculture” on the right side. Also see http://www.nsf.gov/statistics/nsf10318/pdf/tab35.pdf, which shows some difficulty ag graduates have getting employed in agriculture.) It is definitely not a growing field in terms of number of people employed in it (http://www.bls.gov/emp/ep_table_102.htm).
But if your family has a farm or you have passion and ability in the science of it, there is a point in pursuing it. (Some people don’t mind the idea of getting a degree in a discipline and then never working at it, but I don’t care to encourage that.)