Organization: University of Minnesota, Department of Soil, Water and Climate
Application of sulfur (S) to field crops has increased the profitability of many acres in Minnesota. Many research projects have shown the benefits to this nutrient. However, research has not been able to fully cover all of the important aspects of sulfur management. Rate of mineralization from organic matter, efficacy of using elemental sulfur, S credits from manure, normal values for plant tissue tests for S and the cycling of S from one year to the next have not been fully addressed by research. Some studies have been designed to look at this, but have not been able to completely answer these questions due to lack of funding to run samples collected but not sent to the lab. We propose a one-year study to finish analyzing samples collected in other research projects, and one new study to determine sulfur and nitrogen mineralization for soil samples across the state of Minnesota. The data provided will be essential to fill some of the gaps we have in the knowledge base. The end product will be a new sulfur bulletin for the state of Minnesota.
Sulfur significantly increases the yield of corn grown following soybean on low organic matter soils and when corn followed corn. Application of sulfur at planting or as a side-dress application at the V5 growth stage resulted in a similar increase in corn grain yield.
Soil tests were not helpful in predicting when corn would respond to fertilizer S. Plant tissues (whole corn plants at V5 and soybean trifoliate samples at R2) were slightly better at predicting where a response to S would occur.
Sand-separated manure is likely more available nitrogen than normal scrape-and-haul or pen-pack manure (80-90% fertilizer equivalency value compared to 60-70% for pen pack manure). For the source tested, using first- and second-year nitrogen (N) credits from book values likely will underestimate first-year and overestimate second-year availability. Sulfur availability was assessed at 40% for liquid swine manure, 40% for pen pack dairy, and 45% for sand separated dairy systems (equivalency compared to commercial fertilizer).
Sulfur mineralization in soils is highly related to the organic matter concentration in the top six inches of soil. Oxidation of elemental sulfur can progress quickly with most of the elemental S being oxidized within a month of application as long as there is adequate temperature for oxidation and the elemental sulfur source is ground fine enough to increase the reaction time.