Alternative Sulfur Fertilizer Sources for Canola

Date: August 1998
Term: 1 year
Status: Completed
Researcher: Dr. Jeff Schoeneau, University of Saskatchewan
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a

Project Summary

Researchers conducted a field study in 1995 near Star City, Saskatchewan in the Gray soil zone, which compared the effectiveness of different sulfur forms added as sources of fertilizer sulfur for canola. The research showed a sulfur fertilization rate in the range of 15-25 kg S/ha was adequate. Powdered elemental sulfur alone was the least effective and ammonium sulfate was the most effective in increasing sulfur availability and increasing yield. The waste gypsum sources were nearly as effective as ammonium sulfate, making it an effective means for canola producers to economically increase sulfur availability in sulfur deficient soils of the Gray soil zone.

Canola is a crop with a high demand for sulfur, about double the requirements of cereals. Without adequate available sulfur in the soil, severe yield losses can occur in canola. Therefore, sulfur is routinely added to the fertilizer blend, even in soils that test relatively high in plant available sulfur. In the mid 1990s, the two main forms of sulfur fertilizers used in western Canada were elemental sulfur products and ammonium sulfate. However, other sulfur sources existed in western Canada that had not been explored for their potential value as sulfur fertilizers for crop production.

Researchers at the University of Saskatchewan conducted a field study in 1995 near Star City, Saskatchewan in the Gray soil zone, which compared the effectiveness of different sulfur forms added as sources of fertilizer sulfur for canola. The objective of the study was to evaluate the effectiveness of two sulfur fertilizer product concepts: powdered elemental sulfur mixed with sewage sludge and lime; and waste wallboard and mining gypsum in comparison with powdered elemental sulfur alone and standard fertilizer grade ammonium sulfate. In the study, the sources were compared and assessments were made of differences in plant sulfur concentration and uptake, residual soil sulfate and yield response.

Six different sulfur fertilizers were prepared for the experiment, and each product was applied at four different sulfur application rates of 0, 20, 40 and 80 kg S/ha. Ammonium nitrate was added to each plot to ensure that N deficiency did not limit yield. The plot had also received anhydrous ammonia at a rate of 100 lb N/acre the previous fall. The sulfur fertilizers were broadcast and incorporated on May 9, and one week later plots were seeded to Argentine canola (var. Garrison) using an International 7400 drill.

Overall, a significant increase in mid-season dry matter yield was observed in response to increasing rates of sulfur fertilizer. However, rates of sulfur above 20 kg S/ha did not result in significant increases in final grain and straw yield, but did result in increased sulfur uptake and accumulation of residual sulfate in the soil. Therefore, it appears that a sulfur fertilization rate in the range of 15-25 kg S/ha would be satisfactory in ensuring adequate sulfur nutrition of the canola crop under conditions present. (Table 1) and (Table 5).

In the year of application, powdered elemental sulfur alone was the least effective in increasing sulfur availability and yield of canola, and ammonium sulfate was most effective. The observed lower sulfur availability and yield response from the elemental sulfur source is due to incomplete conversion of the elemental sulfur to the plant available sulfate form in the soil in the year of application. The waste gypsum sources performed nearly as well as the ammonium sulfate, pointing to the possibility of using such sources of sulfur as another means to increase soil sulfur availability in the Gray soil zone. The elemental sulfur sources resulted in yield increases of approximately 0.2 T/ha compared with yield increases approaching 0.4 T/ha with the ammonium sulfate and gypsum sources. (Table 5)

Overall, the waste gypsum sources evaluated in this project could be an effective means for canola producers to economically increase sulfur availability in sulfur deficient soils of the Gray soil zone. Other product possibilities include the combination of powdered elemental sulfur with lime and sewage sludge to produce a pellet or wafer of high sulfur analysis, which can be easily handled and applied, but also oxidizes relatively rapidly. Such products may be worthwhile considering for producers who desire a slow release type of sulfur source that is applied once at a high rate and then slowly released into available forms over a number of years.

Note: Scroll to page 3 to view Table 1 and page 4 to view Table 2.

Table 1. Average values for mid-season biomass and final grain and straw yield as related to sulfur rate and source.

Table 2. Average residual soil sulfate levels (end of season) and sulfur fertilizer use efficiency (SUE) as related to sulfur rate and source.

Full Report PDF: Alternative Sulfur Fertilizer Sources for Canola