Large areas of the corn belt have received heavy spring rains each of the past four years.  Aerial photos and road surveys over this period have shown widespread and often severe N deficiency symptoms in corn fields.   Comparison of yield maps with aerial photos shows that the yellower the corn, the lower the yield.  Eleven rescue N trials on fully-fertilized fields with deficiency symptoms have given an average 34 bushel response to rescue N.  The greater the visual deficiency, the larger the yield response has been.