I was unclear of the definition of combine so here it is from dictionary.com which took it from the Columbia Encyclopedia. 

"Combine, agricultural machine that performs both harvesting and threshing operations.  Although it was not widely used until the 1930s, the combine was in existence as early as 1830.  Early combines were traction-powered and drawn by horses, or later, driven by steam internal-combustion engines.  Self-propelled units appeared in the 1940s and have been adopted worldwide.  Modern units feature dust-free, air conditioned cabs and can handle more than 100 acres (41 hectares) of grain per day.  Originally developed for cereal grains, the combine has been adapted to legumes, forage grasses, sorghum, and corn.  The basic operations of the combine include cutting and gathering the standing crop, threshing the seed from the stem, separating the chaff, collecting the seed in a hopper for a delivery to a truck, and returning the straw to the ground.  the combine has replaced the reaper; the binder, which cut and bound a harvested crop into bundles ready for threshing; and the thresher. See C. Culpin, Farm Machinery (12th ed. 1992)