Written by Jonathan Eisenthal

The 2018 Innovation Grant Program is underway, with 12 farmers receiving grants from Minnesota corn to lead projects focused on nitrogen management. Throughout the summer we will be highlighting ongoing projects focused on how to better manage nitrogen and protect water quality. To learn more about each completed and ongoing project, click here.

While lots of attention gets paid to nitrogen as the most immediate limiting nutrient in the corn plant’s development, sulfur, which is needed by the corn plant particularly during grain filling, can get overlooked.

The fact is that many farmers are now finding there is a yield response to fertilizing with sulfur, and Innovation Grant Program participant Brian Ryberg, who farms in Buffalo Lake, is one of them.

“We’re seeing yield bumps with sulfur,” said Ryberg. “We’ve been using Ammonium Thiosulfate (ATS) as a regular part of our fertility program. So we decided we wanted to find out at what level does that response to sulfur end.”

Ryberg received an Innovation Grant to do a four-times replicated trial on strips across 80 acres, where he applied rates of zero (for a control), 10-, 20- and 30-gallons of ATS. AMS is a plant-available form of sulfur, but, like nitrate nitrogen can leach from the soil. ATS is a more stable form of sulfur that requires microbial action before it becomes available for the plant to take it up. This process can take up to two weeks.

A number of factors have conspired over the last decade to produce sulfur deficiency in corn.

First among them has been the major reduction of atmospheric deposition of sulfur thanks to clean air programs that have reduced sulfur emissions from both vehicles and power plants. One study in Indiana showed that rates of deposition had dropped from between 15 to 18 pounds per acre, down to ten pounds per acre (Camberato, Casteel, Purdue University).

The major source of sulfur for crops is the soil itself. Organic matter in the soil can produce up to a hundred pounds of sulfur per acre. Soils that are low in organic matter, sandy soils particularly, can leave crops sulfur deficient.

Ryberg’s soil isn’t sandy, but another feature of his operation can impact sulfur levels—reduced tillage. Because corn and soybean residue lack sulfur, micro-organisms use some of the sulfur in the soil in order to consume that additional residue. This can lead to sulfur insufficiency in the early spring.

For all these reasons, testing the maximum return to adding sulfur fertility should be a highly valuable data set for Minnesota farmers.