While reading the 2012 Annual Farm Progress Reports from Iowa State University's Northern Research Farm in Kanawha, IA, we discovered another trial investigating sulfur fertilization via gypsum on corn. The impetus for the study was the same as the Iowa Soybean Association's; sulfur deficiencies are becoming widespread in both corn and alfalfa in Iowa and many other midwestern states. The experiment was performed by Dr. John Sawyer and David Rueber of Iowa State University.
Four rates of sulfur (5, 10, 20, 40 lbs/A) were applied to two different soils—one with low organic matter and a slope, and one with higher OM and less slope—as was a non-treated control (no sulfur) to compare differences throughout 2011 and 2012. These rates were applied to corn in 2011 and soybeans in 2012. The 2011 plots were planted to corn after soybean in 2011 and planted to corn again in 2012 to test residual effects of sulfur application. In 2012, additional plots were planted to soybean from corn the previous year.
In June 2011, corn leaf greenness was visibly different among plots that had sulfur applied vs. those that did not, as well as having taller plants. By late June, there was still a height difference but the color differences were diminished. Despite visual differences, there was no difference in yield between the treated and non-treated pltos.
This is where it gets interesting...
In 2012, the plots that had received sulfur in 2011 showed no visible differences from those that did not, unlike the differences in 2011. However, when harvest time came, there was an increase in corn yield for sulfur treated plots as a whole when averaged and compared against the non-treated control plots. So, there's something happening with the sulfur in the soil from year to year that isn't being accounted for that has increased corn yield as a residual effect. This is similar to what we saw with the Iowa Soybean Association On-Farm Network trials over the last few years; residual activity from sulfur application making a yield difference a year after we thought it would.
Soybeans did not show any statistically different response to the sulfur application in 2012.
This study will continue in 2013 and we are excited to see the results.