However, if you try a more modern source, like the American Heritage English Dictionary, you'll find a primary definition of culture which is substantially different than either of the two given above: "The totality of socially transmitted behavior patterns, arts, beliefs, institutions, and all other products of human work and thought." Why such a difference, and in such a (relatively) short period of time? Well, in the past 40 years, the use of the word "culture" has been heavily influenced by the academic fields of sociology and cultural anthropology. These fields have gradually brought what was once a minor definition of culture (the last of eight definitions given in the old 1958 Webster's quoted above) into the mainstream.
It is easy to imagine how the U.S. society which was so focused on "socially transmitted behavior patterns" in the sixties would come to need a word to describe the object of its interest. The civil rights movement during this era brought everyone's attention to bear on cultural differences within U.S. society, while the Vietnam War served to emphasize the position of the U.S. culture in relation to other world cultures.
Over time, these new uses for the word culture have eclipsed its older meanings, those associated with cultivation of the land and the production of crops. You might say that an aspect of U.S. culture over the past 40 years is its fascination with the issue of culture itself -- a fascination which has brought about many changes in the way we speak and the meanings of words which we commonly use.