Subsistence Farming: planting crops to "subsist" off of - to live off of as first priority; if any excesses, than the crops cn be used for trade or to sell. Often you will find plots with diverse strains and multiple types of crops - ie, intercropping.
Cash Cropping: planting plots with only one type of crop (ie, mono-cropping) with the main purpose of using the crops for sales purposes only. Mostly, the crops are grown with export in mind.
Benefits of Subsistence Farming:
by Mieke Brouwer - Spring 97
Plant illustrations by Mary Frances Jackson
'Food for Life' is a start... http://www.caa.org.au/AWARE/1996/june-1996.html
Agricultural patterns: traditional vs. conventional