Principal Investigator: Dr. John Lauzon
Research Institution: University of Guelph
Timeline: April 2018 – March 2021
- Determine the existence and extent of sulphur deficiency and yield response to sulphur fertilization throughout Ontario for corn, winter wheat and soybean.
- Determine the maximum economic rate of sulphur fertilization for corn and wheat.
- Collect and save soils from all experimental sites with associated yield data in anticipation of developing and calibrating a sulphur soil test in future work.
- The collection of soil and associated yield data may lead to the future development and calibration of a sulphur soil test that would inform growers of which fields are most likely to respond to applied sulphur fertilizer to avoid costs related to unnecessary application.
- The determination of the extent and degree of sulphur deficiency and lost productivity across Ontario will allow for the development of best management practices to increase profitability and reduce input expenses in cash crop production.
Application of sulphur fertilizer to corn and wheat has become commonplace in Ontario, even though the likelihood of increased yields is currently unknown. No soil test capable of predicting yield response from sulphur has been developed for Ontario. Our previous research trials have shown benefits from sulfur in alfalfa and canola at around 25% of locations tested. Recent work has indicated that responses to sulphur, particularly in corn and soybean, may not be as great as the previous anecdotal evidence suggested. However, sulphur deposition rates appear to be continuing to drop, which may increase the need over time, and there appeared to be significant year to year and site to site variation in response. As such, continued work is required to assess the response over more varied conditions. In 2017, over 2 million acres were planted to corn, and 1.2 million acres to cereals in Ontario. Application of sulphur to these areas represents a large expenditure by growers with little scientific evidence of increased yield. The probability of response in corn and cereal crops is not known, but unlikely to be more than for the higher sulphur uptake crops.
This project investigated sulphur response of corn, soybean and winter wheat grown in Ontario. We undertook sulphur trials for three years meeting scientific criteria for evidence on corn grown after wheat, and cereals grown after soybean and soybeans grown after cereals using two studies. The first group of studies were at the Elora Research Station from 2018 – 2020 and had a range of sulphur rates (0, 10, 15, 20, 40 kg sulphur/ha) from potassium sulphate. Soil samples were collected at the time of fertilization from 0-15 cm depth and 0 – 30 cm depth to be analyzed by 4 potential soil test extraction procedures. At harvest, yield, test weight, moisture, protein and sulphur concentration in both the grain and the stover was measured.
The second study involved on-farm trials with farmer-cooperators. In total 41 of these trials were conducted over 3 years to determine the extent of sulphur deficiency across Ontario. These on-farm trials consisted of two treatments: no sulphur and sulphur applied at about 20 kg sulphur/ha (applied using the farmer’s standard fertilizer application methods). Information on the field site conditions was collected at each on-farm trial including weather, soil type, slope, cropping history and manure application history. Soil samples were taken around the time of fertilizer application. From each site soil samples were collected at the time of fertilization from 0-15 and 0-30 cm depth and grain yield was collected at harvest. Soil samples collected from both the intensive sites at Elora and the grower sites are currently being evaluated with the 4 potential extraction procedures identified in the greenhouse trials explained below. The results of each extraction will then be compared to the field grain yield and economic responses to applied sulfur to determine which extraction procedure may best identify responsive sites under field conditions.
Greenhouse Trial Results
A total of 60 soils were collected from across Ontario to represent a wide rage of soil texture, soil pH and organic matter content. Five potential extraction procedures were used to measure soil test sulfur on each of the 60 soils. A very high sulphur requiring plant, mustard, was grown on each soil in the greenhouse with and without applied sulphur fertilizer. Plant sulphur uptake in the non sulphur fertilizer pots and the increase in sulphur uptake from fertilization was then correlated with each of the potential soil test procedures to determine which best correlates with plant responses.
The mustard plants grew well in the greenhouse with an average biomass of 2.4 and 3.1 g pot for the no sulphur and sulphur applied treatments respectively. Although plant biomass was increased with added sulphur fertilizer, the concentration of sulphur was increased to a greater extent. This resulted in an even greater numeric increases in total sulphur uptake. The biomass production and S uptake was quite variable from one soil to the next, as such the increase in sulphur uptake was represented as a percent increase over the check to normalize the values for statistical analysis.
The five different extraction procedures gave numerically different values. However, these extracted values were all well correlated with each of the other extractions (R2 > 0.91 in all comparisons between soil test measures) except for the sodium bicarbonate extraction, which did not correlate well with any of the other extraction procedures (R2 <0.39 in all cases). The strong linear correlations and “tight” fit of data in regression analysis in each comparison opens the possibility of converting values obtained from one extraction into another. However, more work needs to be done to compare the extractions over soil test levels that crop response occur, instead of the entire range, to ensure the conversion is sound in the range of soil tests that are agronomically important.
Results from regression analysis comparing the soil test values to measures of crop sulphur uptake for the non fertilized treatments found that all but the sodium bicarbonate extraction resulted in similar correlations with plant uptake. For all extraction procedures there was a linear increase plant sulphur uptake with increasing soil test for the non sulphur fertilized pots. It was also found that the relationship between the soil test measure and plant sulphur uptake was not significantly impacted by the soil organic matter level, soil pH or soil texture. Given the strong correlation between all soil tests, other than the sodium bicarbonate, it is not surprising that they all gave similar relationships with the plant uptake. Further work was done to compare the soil test levels measured with the percent increase in plant sulphur uptake with the fertilized treatments compared to the unfertilized. In this case, the increase in uptake decreased with increasing soil test level up to a point where the plant no longer responded to fertilization, presumably because the soil was providing enough sulphur to meet plant requirements. It should also be noted that, except for the sodium bicarbonate extraction, all comparisons of the soil test levels with the percent increase in plant sulphur uptake resulted in a tight pattern of data, which indicates they are predicting sulphur fertilizer responsive soils well.
The results observed for this analysis would suggest that the sodium bicarbonate extraction is not a good choice to move forward with. However, all other extractions show promise. Of the extraction procedures tested, the water extraction gave the best correlations with plant uptake; however, all extractions, except the sodium bicarbonate, gave a good relationship with plant uptake and plant response to applied sulphur. Water extractions are commonly used in some jurisdictions of western Canada for determining sulphur. Although the water extraction was slightly superior, compared to all other extractions the water extraction required a far greater amount of time (about 3x to 4x greater) to filter the sample. This extra time may make the use of water extractions less practical in commercial labs. In addition, it was also found that many of the available calcium phosphate chemical supplies had significant amounts of sulphur in them and/or had limited solubility in water. This does not preclude the extractant, but care should be taken to use low sulphur sources and to analyze a sample of extraction solution to give a base line sulphur level which is subtracted from the soil extraction values to avoid overestimation of soil sulphur levels.
Since there was no clearly superior extraction of the 4 of the 5 procedures tested (nanopure water, calcium chloride, potassium phosphate, and calcium phosphate) we have started to compare all 4 of these extractions to all the collected field response data. Even though the greenhouse trial indicated the potential for converting values of one extraction to another, it is important to evaluate all of them to determine how good the correlation of extractions will be within the agronomically important soil test range found in the field testing. The greenhouse data indicates the potential of a sharp soil test cut off point between soils that result in plant response to applied sulphur and those that do not. This further raises the possibility of a simple soil test that indicates when sulphur is required or not, instead of determining variable sulphur fertilizer recommended rates. Due to the generally low sulphur fertilization rate of application required and observed (20 kg S ha-1) in the field portion of this trial, a simple yes or no answer to sulphur fertilization may also be a reasonable approach to sulphur fertilization and increase the potential success of the calibration.
Field Trial Results
Field trials were conducted on a total of 43 sites from 2018 to 2020. Two types of sites were conducted, simple with or without sulphur applied sited to determine responsiveness of the site to sulphur, and multi-rate trials to also determine the rate of sulphur required. Originally it was planned that only one site of each crop at the Elora site would have the multi rates; however, several other sites also provided multi rate trials.
The results from all trials indicate that winter wheat is the most likely crop to respond, and soybean rarely responded to applied sulphur. In total only 3 of 22 soybean sites responded. Of these 3 sites, the response at 2 of the sites was attributed from field observations to more likely be from the ammonium in the ammonium sulphate applied at the sites. With these 2 sites removed from the overall economic analysis, application of sulphur was found to result in a net reduction in income. For corn, 3 of 8 corn sites responded to the application of sulphur. Although the overall economic analysis resulted in a net increase in income of $31.48 ac-1, caution should be used as most of this overall effect was the result of one highly responsive site (Elora 2020), which had a 58 bu ac-1 yield increase with sulphur fertilization. For winter wheat, 8 of 13 winter wheat sites had a significant response to applied sulphur fertilizer. This resulted in an overall economic impact of $21.99 ac-1 when all sites were considered together. This work would indicate that simple blanket sulphur fertilization in Ontario is likely to reduce farm income for soybean, and the inconsistent responses seen on corn and winter wheat point to the need to identify responsive sites. This would greatly increase farm income by not only achieving yield response in responsive sites but reducing fertilizer costs in sites that are unlikely to respond. For instance, average income would increase from -$3.55 ac-1 to $20.62 ac-1, $31.48 ac-1 to $92.48 ac-1, and from $21.99 ac-1 to $54.19 ac-1 if fertilizer was only applied at responsive sites for soybean, corn and winter wheat respectively. These values would translate to an increase of $32.2 million increase in Ontario farm income for winter wheat alone, assuming 1 000 000 acres of winter wheat over the current approach of blanket application of sulphur on all winter wheat land in Ontario. Although there were inconsistencies in response, in the trials that did respond to applied sulphur, generally 20 kg S ha-1 was sufficient to meet the demand of the plant for all three crops.
The inconsistent results seen for crop response to applied sulphur in the field trials further indicates the need to identify sulphur responsive sites. The sulphur test will never give a perfect representation, but the results from the greenhouse trial in this study indicate a good potential of 4 of the extractants. The original plan was to analyze only one promising extraction procedure on the field samples; however, the greenhouse trial did not show a clearly superior extraction of the 4 promising ones found. As such we have started the analysis of all four on the collected samples from the 43 field sites to see if the extraction procedures perform differently in field conditions. If they also perform similarly in the field, then discussions with the Ontario commercial labs will be used to determine which procedure is most appropriate to go forward with based on the ease and cost of the lab procedure.
External Funding Partners:
Ontario Agri-Food Innovation Alliance, a collaboration between the government of Ontario and the University of Guelph
Project Related Publications: