Where it is certain boron is needed (otherwise shouldn't be applied because of the danger of toxicity), the rate per acre according to this and other ag sites is 0.5 to 1 lb per acre of actual boron.
http://corn.agronomy.wisc.edu/...
According to this page, borax is typically 11% actual boron (does it say on the box?). On that basis my math, which should be checked, suggests the amount per 1,000 sq. ft. would be roughly 2-4 oz. That was rounded to assume 10% rather than 11% actual boron to make it easier.
How I calculated: 5-10lbs of borax is needed to supply 0.5 to 1.0 lb per acre of actual boron. An acre is 43,560 sq. ft. So divide 5-10 by 43,560 for amount per sq. ft. and then x 1000 gives 0.11to 0.23 of a lb. of borax per 1,000 sq. ft. At 16 oz. to the pound that would be (roughly) 2 to 4 ounces. Am I right?
Edited to remove inappropriate % signs - see next post
