There is no one right answer to this question. The higher the channel count, the higher the fold (for any given shot interval), and the higher the signal/noise ratio. For land seismic, we generally recommend 24 or higher-fold data. If the shot spacing is equal to the geophone spacing (typical), this means that you must record on at least 48 channels with each shot. In addition, you must have extra channels for electronic rolling. Taken together, this means that for land CDP reflection, you should have a minimum of 72 channels, which will allow you to roll 48 live channels through a total of 72.