The benefits of PRO CAL 40 in decreasing Platte Valley Yellows or iron chlorosis appear to last only one year. Although we saw yield benefits the second year in the corn (6-15 bushels better) we did not see visual differences when we rotated back to soybeans in the third year.
The data below is from research that was done by Dr. Wiese, etal. while he was at the University of Nebraska. He used granulized gypsum at lower rates in the row and saw similar responses as we experienced.