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Issue No. 1, Article 6/March 25, 2011

Sulfur for Corn: Feast or Famine

As many of you probably know, in 2009 we started a study to evaluate corn response to sulfur in Illinois. From this research we have found so far that most fields are not responsive to sulfur, but those that are are typically very responsive. Following is an update of results and a request for volunteers.

On-farm results. Averaged across all fields (10 sites), we observed an increase of 4 bu/acre in yield with sulfur, but we could not determine statistically that the increase was due to the sulfur application. Only two sites (20% of tested sites) showed a statistically significant increase in yield with sulfur application. The two sites were in Menard County in an Onarga sandy loam and in Iroquois County in a Milford silt loam. The field in Menard County produced a 51-bu/acre increase in yield (167 bu/acre without sulfur and 218 bu/acre with 30 lb sulfur/acre). The field in Iroquois County produced a 20-bu/acre increase over the unfertilized check. Sulfur application in another site in Woodford County produced 222 bu/acre yield, which was 8 bu/acre greater than the check, but the difference was not statistically significant.

Small-plot results. As with the on-farm trials, 12 site-years of data from small-plot research showed overall no statistically significant yield increase (a 7-bu/acre yield increase compared to the check with an application of 24 lb sulfur/acre). However, the sites that were responsive to sulfur showed substantial yield increases. In Champaign County on a Wyanet silt loam, an application of 24 lb sulfur/acre produced 208 bu/acre and a 26-bu/acre increase relative to the unfertilized treatment. In Lee County on a Wyanet fine sandy loam, the same rate produced a 209-bu/acre yield, which was 25 bu/acre greater than the unfertilized plot.

What do these data tell and not tell us? To date, the amount of data we have is insufficient for any broad conclusions. So the fact that we saw a large increase in yield in a Onarga sandy loam does not necessarily indicate that people with that soil should apply sulfur. Similarly, the yield increase we observed in Champaign County should not be taken as an indication that fields in that county would benefit from a sulfur application. What these data do clearly indicate is that there are fields with a lot of potential for response to sulfur, while others are very unlikely to respond.

Our current results, although limited, contrast with work done in the late 1970s in Illinois. Out of 82 sites, only five (6%) showed a significant response to sulfur. The average response for those sites was 11 bu/acre, and the average increase with sulfur application for the remaining 77 nonresponsive sites was only 0.5 bu/acre. The frequency of sulfur deficiency and the magnitude of yield response to sulfur application seemed to have increased since the late 1970s. Several factors may be contributing to this change. Strict air pollution standards have cleaned the air of gaseous sulfur compounds, resulting in less sulfur atmospheric deposition. In general, many agronomic inputs, such as fertilizers, insecticides and fungicides, are "cleaner," having less incidental sulfur in them. Also, fewer livestock operations across the state have led to less application of manure, further reducing the amount of sulfur being applied with this fertilizer source. At the same time that less incidental sulfur is being applied or deposited, there is more removal of sulfur by increasing crop yields.

Still, at this point, the only way to determine whether a particular field could be responsive to sulfur is by conducting a test trial. As in the previous two years, I am looking for volunteers throughout Illinois to participate in on-farm research to measure corn response to sulfur fertilization. Your participation would provide useful information on your particular field as well as improving our ability to predict more broadly where sulfur applications are most needed.

If you are interested in participating (even if you are not sure whether your particular field or equipment would fit the conditions described), or if you have questions about how to find sulfur fertilizer or have the fertilizer applied, please contact me: fernande@illinois.edu; 217-333-4426; Department of Crop Sciences, N-315 Turner Hall MC-046, 1102 S. Goodwin Ave., Urbana, IL 61801.

Soil conditions. We would like to characterize sulfur response across the state, so we will consider all soil types. However, we are especially interested in light-colored soils (less than 2% organic matter, coarse texture, or both) and soils with an eroded phase. The only fields we will not consider are those that have received manure or sulfur applications in the last 5 years.

Equipment. Volunteers conducting these trials follow a simple design applying 0 and 30 lb S/acre as a broadcast application in a uniform portion of the field. A minimum of three replications or as many as eight are needed for each field. Figure 7 shows a layout of the treatments randomly assigned within each replication for an eight-replication study. It will be important to georeference or clearly mark each strip with different-colored flags or markers in the center. Strips can be anywhere from 8 to 16 rows wide by 300 to 1,000 feet long. What is important is that the size of the strip allows accurate application of rate and accurate measurement of yield, and if possible that the strips be wider than the harvest strip. However, if the combine is at least 12 to 16 rows wide, it is possible to harvest the strip without having border rows.

Figure 7. Layout of the treatments randomly assigned within each replication for an eight-replication study.

Sulfur sources. While there are sulfur sources we prefer, we can accommodate others that may be available to you. We prefer the use of ammonium sulfate (NH4)2SO4 (21-0-0-24); MicroEssentials sulfur (ME S) ME S15 (13-33-0-15); or elemental sulfur (0-0-0-90). If the sulfur source contains other accompanying nutrients, the corresponding rates of those nutrients need to be applied to other treatment strips to avoid a differential response to nutrients other than sulfur. If you use ammonium sulfate you need to apply 26 lb N/acre to the other strips, and if you use ME S15 you need to apply 145 lb DAP (18-46-0)/acre.(For more details see "Applying the treatments" below.)

Time of application. Our preferred application time is preplant, since visual response to sulfur is typically observed early in the growing season. Also, if elemental sulfur is used, the earlier this source can be applied ahead of the crop, the more chance there is for that sulfur to become plant-available for this year's crop.

Measurements for data collection. The only data volunteers will have to provide is the yield for each strip. This information can be collected by yield monitor or from a weigh wagon. Volunteers will not be required to take plant or soil samples, but would need to allow the researcher to visit the strips approximately two to three times during the growing season.

Applying the treatments. There are three sulfur sources to choose from:

•ammonium sulfate (21-0-0-24)

For strips with 30 lb sulfur/acre: Apply 125 lb ammonium sulfate /acre.

For the strip with 0 lb sulfur/acre: Apply 26 lb nitrogen/acre. This application is made to balance the nitrogen that was applied along with the sulfur in the sulfur strip. Those 26 lb of nitrogen/acre can be applied as either 57 lb urea/acre, 94 lb UAN (28%)/acre (8.7 gallons/acre), or 82 lb UAN (32%)/acre (7.4 gallons/acre). Do not use anhydrous ammonia because it would be difficult to apply only 32 lb of product/acre.

•micro essentials MES-15 (13-33-0-15)

For strips with 30 lb sulfur/acre: Apply 200 lb MES-15/acre.

For the strip with 0 lb sulfur/acre: Apply 145 lb DAP (18-46-0)/acre. This application is made to balance the nitrogen and phosphorus that was applied along with the sulfur in the sulfur strip.

•elemental sulfur (0-0-0-90)

I would use elemental sulfur only as a last resort, because often all of it does not become available in the year of application.

For the strip with 30 lb sulfur/acre: Apply 33 lb elemental S/acre.

For the strip with 0 lb sulfur/acre: There is no need to apply any product because the sulfur source is not accompanied by any other nutrient.

Additional N, P, K, or other inputs. If the field needs additional nutrients or other inputs (insecticide, herbicide, etc.) to optimize production, make sure those inputs are applied at the same rate across the entire study site.--Fabián G. Fernández

Fabián Fernández

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