I am trying to choose a datalogger for Soil Water content monitoring in a remote, harsh area, either using the CS616 or the CS650 probes. I would like to know which is the maximum number of probes (CS616/CS650) that can be connected to the CR300 and CR800 dataloggers, both have 6 single-ended ports (3 individual). For the CR200x series it is indicated that a maximun of 4 CS616 probes can be connected at a time (5 single-ended analog ports).
The CS616 is not compatible with the CR300. A similar prober, CS625, is compatible. These types of sensors require a period average input. Four of the channels on a CR300 are capable. On the CR800, 6 channels are capable. You could connect more sensors by using a multiplexer.
The CS650 has a SDI-12 output. Both the CR300 and CR800 have two channels capable of SDI-12. With setting unique SDI-12 addresses in your sensors, you may connect 10 sensors to one channel. If cable lengths aren't excessive, you can even connect more than 10. You will just have to deal with physically connecting multiple sensors to one channel by using terminal strips.
In addition to the CS650, consider the CS655. It is the same sensor technology with shorter rods to allow higher conductivity soils. These sensors automatically adjust for temperature and conductivity to provide a more accurate measurement than a CS616.