Nitrate nitrogen losses from corn and soybean crops can be 30-50 times higher than from perennial crops such as alfalfa, according to Gyles Randall, a University of Minnesota soil scientist.

A study on nitrate losses from subsurface tile drainage has been going on at two southern Minnesota locations since 1973. Randall says greatest losses occur in wet years following unusually dry years. Seventy percent of the annual nitrate loss occurs in April, May and June.