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Sulphur strategies

Sulphur was applied in this demonstration field to evaluate the yield benefit and economics of the practice. Photo by Peter Johnson, OMAF. 

Whether or not to apply sulphur on a field has been a topic of hot debate in recent years in Ontario – when to add it, how much, in what regions and on what crops are all factors for consideration. Canola is the crop most responsive to sulphur; soybeans are unlikely to respond to extra-added sulphur in Ontario soils.

Two centuries ago, when industry started to boom in southern Ontario and the neighbouring areas of the United States, sulphur was deposited on the soil through acid rain, so much so that the practice of adding sulphur to fields was stopped during the 1850s. However, sulphate deposition from acid rain and snow has decreased significantly in the past 15 years, says Scott Banks, emerging crop specialist with the Ontario Ministry of Agriculture and Food and Ministry of Rural Affairs (OMAF and MRA). This is because of anti-pollution legislation being passed, the availability of better air quality technology, and the recession – which some say is the biggest factor in decreasing the amount of sulphur coming down from the skies.

Sulphur (S) application also needs a close look these days because fertilizers, insecticides and fungicides are cleaner, and contain less incidental S. There have also been some long-term decreases in livestock farming in Ontario, which means fewer fields are receiving S through manure applications, and ever-increasing crop yields means more S and other nutrients are being removed from the soil.  

Whether S needs to be added to particular soils is dependent on a few factors. Soil tests are not terribly helpful, however, in determining what to do, because S cycles from soil organic matter into the soil solution and back again. In other words, part of the time it’s unavailable. In soils with a lot of calcium, sulphur combines with the calcium atoms, goes back into solution and back to binding with calcium again, depending on how much calcium is present, the type of soil, and whether or not the sulphur is exposed to the open air. However, soil testing for S at the same time every year may provide a sense of any long-term trend. Soil pH is not a factor that affects sulphur availability to crops, and results of studies looking at S and soil type have been inconsistent. Plant tissue sampling looks to be better at determining S deficiency.

Banks has been conducting trials to help with decisions relating to the application of sulphur for winter and spring wheat. “We are evaluating the yield benefit and the economics,” he says. “The project farm co-operators include Mark McFaul, Henry Nyman and John Nanne, the Ontario Soil and Crop Improvement Association (OSCIA), and OMAF field crop technician Victory Yuill.” Local agri-business suppliers have provided other support.  

At each field location in Ameliasburg, Wellington and Pakenham, two treatments were employed – no S and S (20 kg/ha of available S), with equal amounts of total nitrogen (urea) applied as per the normal field recommendation. Soil samples were taken and harvest was conducted on adjacent strips. Plant tissue samples were collected for analysis from the Ameliasburg and Wellington sites at last-two leaves emergence (Zadok’s Stage 37 to 39) in early June 2013.  At the Wellington site, there was a 4.5 bu/ac increase in average in grain yield in the winter wheat with S application, the only site to show a yield gain. Grain yield in Ameliasburg showed a lower average yield of 2.3 bu/ac with the S application compared to no S. “This lower yield is most likely due to field variability,” Banks explains. “The Pakenham site was hard red spring wheat and resulted in no yield difference. The addition of S did not result in any significant difference in either grain test weight or protein content.” Soil samples were taken in Ameliasburg to compare S and organic matter levels at zero to six-inch depths.  

The plant tissue analysis was inconclusive. “We currently don’t have an established critical value for S in plant tissue in Ontario,” notes Banks. “There is some research from Australia that shows the critical value for wheat plant tissue collected at the stage we collected is 0.3 per cent. We got that 0.31 at the Ameliasburg site where we did not apply S, and 0.35 where S was applied. As both treatments were above 0.3 per cent and there was no yield advantage at this site to applied sulphur, the critical value of 0.3 per cent may be a good indicator.”

However, at the Wellington site, the no-S-applied plots had a sulphur tissue level of 0.26 per cent, and 0.27 where S was applied. “That both of these are below the 0.3 per cent level indicates that insufficient S was present, even with the additional 20 lbs/ac of sulphur,” Banks says. “More tissue sampling needs to be done to validate what the critical value is for sulphur in this region of Canada.”

Banks notes that the Wellington site features a stony loam soil type whereas the Ameliasburg site is a stone-free, loam to clay-loam and the Pakenham site is a clay-loam soil type. “Because S is a soluble nutrient similar to nitrogen, the courser-textured soils such as that found at the Wellington site may be more prone to S loss due to leaching. Both the Ameliasburg and Pakenham sites have a history of manure and high soil organic matter levels of four per cent or greater. This may explain why there was no response to added S at the Ameliasburg and Pakenham sites. The greatest response to sulphur seems to be at sites that have not had a history of manure and are low in organic matter.”

The project is being repeated again this season. “We have also expanded the number of sites and the number of tissue samples in order to gain further insight into the critical value for S,” Banks says. 

December 1, 2014  By Treena Hein