MSU Extension

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

The recent decreases in atmospheric S deposition, increases in corn yields, and relatively early corn planting dates have prompted grower and industry interest in the use of S-containing starter fertilizer sources for corn. Six S-starter study locations were evaluated in Michigan in 2005 and 2006, including two sites per year on MSU research farms and the remaining four on producer fields. Sites were located on coarse-textured soils with a minimum or no-till cropping system. Treatments consisted of iterations of starter fertilizer with and without S addition (as ammonium sulfate, ammonium thiosulfate, or gypsum) and were replicated three or four times (Table 1). Plant height, chlorophyll meter readings and plant tissue samples were collected at approximately V4, V6 and R1.

Analysis of the relative leaf chlorophyll content at the research farm sites revealed differences in leaf chlorophyll (greenness) among treatments, particularly at the V6 stage or earlier. Though differences were evident, the only distinguishable trend was that the gypsum treatment (10S) typically had less relative chlorophyll than most other treatments, except the control. Significant differences in plant tissue N and S among treatments were also identified in 2005 and 2006. Where differences were noted, the consistent trend was that the percent of N was less for the control and 10S treatments, as could be expected with the ammonium-based sulfur source, and the percent of S was less for the treatments without S.

Correct interpretation of the yield response data to fertilizer treatment is critical to diagnosing actual crop response to starter fertilizer containing S. Data collected at the research farm sites in both 2005 and 2006 indicate that rather large differences in yield (22 bu/ac and 23 bu/ac at Ingham in 2005 and 2006, respectively) occurred as a result of fertilizer treatment (Table 2). However, the lowest yielding treatment at all sites where a treatment response occurred (Ingham 2005 and 2006, Montcalm 2006) was the control, which received 0 starter fertilizer. At the research farm sites in either year, there were no significant differences in yield among any of the treatments that included some form of starter fertilizer. There were no trends in the data indicating that there was a significant response to the addition of S in the starter fertilizer.

Yield data collected at the on-farm sites indicated that a significant difference in yield resulting from S addition to starter fertilizer treatment was evident at 3 of 7 sites across both years (Tables 3 and 4), and at only 3 of 11 sites when the 25N and 25N+xS treatments at the research farm sites were included in the analysis. The only site that showed a positive response to S addition relative to the N-only starter was Monroe in 2005, where the 25N+20S treatment yielded greater than the 25N-only treatment (189 bu/ac vs. 174 bu/ac). The other two significant site years (Berrien 2005 and 2006) showed a yield decrease for 25N+20S compared with the 25N+5S. This decrease was likely a function of seedling damage stemming from placement of the starter fertilizer with additional ammonical N 2-4” directly below the seed.

The yield responses observed in this study can primarily be attributed to the use of N, P or a combination of N- and P-containing starter fertilizer in general, rather than from the addition of S to the starter fertilizer blend. As atmospheric sulfate deposition continues to decrease, a corn yield response to sulfur is more likely to occur. Sulfur research in other Midwest states is showing hit-and-miss responses to S additions, with some positive yield results reported from states including Ohio, Iowa and Minnesota. For Michigan minimum or no-till cropping systems, particularly on soils with low OM, a response of S addition to a starter fertilizer is possible, but not probable. The likelihood of response should increase in cool, wet springs where mineralization is minimized and early crop growth is slowed. If growers elect to include S in their starter fertilizer program, soluble S sources (e.g. ammonium sulfate, ammonium thiosulfate) should be selected rather than elemental S, which may not be available to the growing crop in a timely fashion.