Jim, this what i have been using to record soil temperatures.
  http://www.onsetcomp.com/products/data-loggers/ux120-006m
 It is designed for indoor use, but i put it in a home made weather proof encloser for outdoor use. It requires external sensors that plug into the logger,the ones i have been using are the air-water-soil sensor TMC6-HD. You also need the hobo ware software, which now can be downloaded for free from onset computer and you need a usb cable.
 

(tmc6-hd temperature sensor.bmp)

(larkins north rye data logger 3 15 2016 001.jpg)

tmc6-hd temperature sensor.bmp (1406KB - 25 downloads)

larkins north rye data logger 3 15 2016 001.jpg (73KB - 30 downloads)