Photo above: 2016 sulfur trial on corn in Kanawha, Iowa at the ISU Northern Research Farm. SO4 applied at 150 lbs/acre (left) and no sulfur applied (right). SO4 application resulted in a 30 bu/acre increase compared to no sulfur.
Expect Sulfur Deficiency
With seemingly endless rainfall this spring, we can expect widespread sulfur deficiency as corn continues to emerge. The problem is that sulfate is easily leached from where the young corn roots need it in wet years. Sulfur deficiency shows up in the youngest leaves of the plant, and consists of green and yellow stripes in the leaves. Many confuse nitrogen deficiency with sulfur deficiency, and the most likely scenario is that it’s sulfur and not nitrogen since most growers typically put out more than enough nitrogen to meet crop needs.
To compound this problem, wet springs often mean that sulfur applications were skipped or postponed in lieu of getting seed in the ground during short windows of opportunity. Further, most sulfur sources that can quickly supply sulfur to the crop via topdress application have high burn potential.
SO4 is the perfect sulfur source for any application scenario, but the ability to topdress SO4 without any concern over crop burn makes it stand out against other sources.
Research conducted at Iowa State University with SO4 has shown that green-up will occur in less than 1 week with topdress applications up to V6.
SO4 Application Rates
How much sulfur you need to apply for your crop depends on your soil type. In coarse textured soils with low organic matter content, shoot for about 25 lbs of sulfur per acre (150 lbs/acre of SO4); for finer textured soils with 3% organic matter or more, application rates closer to 17 lbs of sulfur per acre should suffice (100 lbs/acre of SO4).
It’s hard to accurately predict where and when sulfur deficiency will occur, but you can save your yield potential and correct in-season sulfur deficiency with topdress applications of SO4.