What is the average length for the roots of an Orange Tree?

Answer 1

Citrus sinensis the sweet or navel orange can typically get 25 feet tall but some get to 50 ft. Typical row spacing is 25 feet. http://www.hort.purdue.edu/newcrop/morton/orange.html
In general roots grow about three times the canopy spread. About 1/2 the roots grow under the canopy but the other 1/2 spread beyond the canopy drip line.
http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/trees-new/text/tree_anatomy.html