Applying gypsum, even applying it at variable rates by soil type, is a practice becoming more common these days ahead of corn. The idea is to gain some extra calcium for the soil. And in the process, you also add sulfur. One sulfur product available form a power plant in 2009, for example, had a guaranteed analysis of 21.5% calcium and 16.5% sulfur.
Sulfur was a non-issue 25 years ago. Today, it's starting to show up more often in tissue tests of corn leaves in the summer as borderline or sometimes deficient. Agronomists suspect that the improved methods of removing sulfur from the air that power plants have been forced to switch to over the past three decades is making a difference in how much 'free' sulfur corn plants are picking up from the local atmosphere. This is especially true in coal-producing states where power plants still burn lots of coal.
However, most agronomists stop short of recommending sulfur. Instead, many say it is a micronutrient to keep an eye on. Most universities still do not have data that shows a significant yield advantage to adding sulfur.
Toby Ripberger, manager of Beck's Hybrid Practical Farm Research studies at the home plant near Atlanta, Ind., reports that Beck's have included gypsum trials in their tests the past two years. Unless otherwise noted, most of these are demonstration-type trials.
In small plots in 2008, they saw a sizable yield advantage, up to 20 bushels per acre, for adding gypsum. So they continued the test, planting corn on the same ground, and even adding extra gypsum in one part of the plot. In 2009 the tables flipped, with the part of the field that received no gypsum either year out yielding the other two sections by almost 20 bushels per acre. Overall, the two-year average was less than two bushels per acre better for either of the plots where gypsum was added, vs. the control plot.
"This plot is inconclusive regarding any benefit from the use of gypsum," the plot report states.
However, based on encouraging results in 2008, they set up a separate test applying gypsum in zone-till corn on a larger plot. Several hybrids were tested. The gypsum was applied with a spreader truck. One ton per acre was applied. All hybrids showed a yield benefit for gypsum, ranging from 3.8 to 37.8 bushels per acre, with an average of more than 20 bushels per acre where gypsum was applied.
So is it a phenomenon that only shows up the first year? Are the first year results in both tests just a fluke? Bottom line is that these tests are inconclusive. Flashes of response make it intriguing to try again. In the mean time, based on these results, at least, it would be difficult to justify a large expenditure for gypsum.