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Fitting this macronutrient into a long-term fertility and soil nutrient plan.


May 24, 2019
By Top Crop West Staff

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Sulphur (S) is an important macronutrient for crop production. While canola is most often recognized in Western Canada as a crop that requires the largest amount of S, most crops benefit from proper S fertilization. Like other macronutrients, sulphur helps optimize yield and quality. However, it is only in understanding how sulphur does this, can the reason for its necessity be fully realized.

“In crops, sulphur is particularly important for protein synthesis and is a key component of two essential amino acids, cysteine and methionine, which are needed for that process,” explains Elston Solberg, research agronomist with Sun Mountain Inc. in Edmonton.

“These amino acids are the mediators of the efficient creation of the 18 other amino acids involved in protein synthesis, secondary plant compounds, and protein enzymes required by crops to regulate photosynthesis and nitrogen fixation,” Solberg says. “Sulphur enhances the utilization of every other nutrient. Interestingly, the Mulder chart, which shows synergistic or antagonistic interactions between plant nutrients, does not include S because it plays well with all others.”

Thanks to current research, growers and agronomists can better understand the complexity and functionality of these S-based compounds. A plant loaded with S is able to synthesize and create glutathione, which is an important antioxidant or stress fighter within the plant. Another group of secondary plant S compounds are the glucosinolates, which help plants (brassica species in particular) defend against certain insects and diseases. To support all these functions, adequate S needs to be available to the crop.

Sulphur levels are usually extremely variable across a field, making it challenging to get a representative soil sample, which often results in misleading numbers. It only takes one sample in an overabundant area to totally skew the sulphur test.

“One of the complications with S deficiency is that applying N fertilizer without S in deficient areas will actually decrease yields,” Solberg says. “Therefore, the most important factor to look at is a balanced N:S ratio in plant tissue, which is typically 10:1 for cereal crops and grass forages, 8:1 for pulse crops and 6:1 for canola crops.”

Solberg says this is how he bases sulphur recommendations, regardless of soil test sulphur levels. “How much nitrogen does it take to grow this crop yield? Then I use the appropriate ratio to come up with the sulphur recommendation. The best indicator of adequate S levels in the crop is a tissue test of newer leaves. We take the newer leaves because sulphur is immobile in the plant and can’t be remobilized from older to new tissue, so this is where sulphur deficiency shows up first.”

To ensure crops have adequate S available every year, Solberg recommends including elemental sulphur (ES) as part of a long-term fertility management plan. Plants utilize S in the sulphate (SO4-S) form, and through a biological process, ES is converted to the available form. The key to success with ES is broadcasting and leaving the ES on top of the soil, increasing surface contact and allowing soil microorganisms to find the ES faster and easier. Broadcasting produces the best results, with a 20 to 30 per cent conversion in the first year. Incorporating ES into the soil through banding or tillage, slows the conversion to less than 10 per cent.

Because only a portion of the ES is converted to sulphate every year, the remaining ES stays in the soil until it is converted, acting like a slow-release fertilizer. This, in combination with the large amounts applied once every few years, enables growers to remove a huge amount of fertilizer bulk out of the air seeder tanks and improve logistics. By applying elemental sulphur in fall or early spring, removing the sulphur typically placed at seeding time, seeding efficiency increases by roughly 20 per cent.

Solberg adds, “Because the conversion to SO4-S is a biological process done by the soil microorganisms, soil acidity does not change immediately. The acid added by agronomic rates of ES application will not increase soil pH by significant amounts, and the small amount of biologically produced acid helps release other nutrients that have become crop unavailable. We have lots of research tissue test results since the mid-90s to prove this. On the other hand, he adds, all fertilizers applied, except for potash, create acid extremely rapidly in a chemical process, depending on the product being used, at much higher levels than ES. Ammonium sulphate also has a very high salt index, whereas ES is almost zero.”

Bio-Sul Premium Plus is an ES amended granular compost product that is applied at a variable rate, depending on farm needs. It maintains effectiveness for multiple years, eliminating the need for annual application. “The product is comprised of 70 per cent ES from recovered industrial ES sources and 30 per cent compost from diverted food waste streams,” Solberg explains. “It is custom broadcast by a spin spreader for proper application.”

Solberg adds the biggest consideration when determining application rates is really whether the land is owned or rented. Many growers try to negotiate rental agreements of three to five years, so may back off application rates slightly to fit within those timelines. Overall, using ES, especially Bio-Sul, on a per pound basis is much cheaper than other ES and sulphate products available. “By blanketing fields with higher recommended rates, depending on which product is being used, you are avoiding a yield and/or quality penalty in areas where the N:S ratio would, otherwise, be too wide.”

“For us, one of the main benefits of using elemental S is it takes a lot of product out of the seed drill, which significantly speeds up seeding. It also reduces the amount of fertilizer hauled to the farm and field, wear and tear, as well as the amount of storage space required to handle our annual supply,” says Richard Limoges of Limoges Seed Farms near McLennan, Alta. “If S is no longer in the blend, we can seed a lot more acres per fill, or use the space to apply higher rates of other nutrients. Ensuring proper S fertilization is needed to maintain the correct N:S ratios and is very important in our area in the Peace region for improving nutrient use efficiency and crop performance, in particular crop maturity. Other factors such as oil content and protein levels are also improved by proper S nutrition. In our area, S is generally underapplied, so many growers see a bit of a yield bump when they apply ES at these high rates.”

Nikki Olson, an agronomist with Exactly Ag and farmer near Red Deer, Alta., agrees. She notes taking S out of the blend increases the feasibility of getting the fertilizer blends through the drill. “For growers using variable rate (VR) precision applications, they don’t need as many tanks either. One of the benefits we have seen on our farm and with other growers I work with is that using ES balances out some of our nutrient ratios and helps the crop be more efficient. For example, we have been able to decrease some of our N applications as we have improved the N:S ratio balances, which, in turn, helps to improve the protein and grain quality as well.”

Another benefit, notes Olson, is using elemental S has helped the whole management program on the farm. She’s found that the crop has the required nutrients when needed, even in those sulphur-heavy years with canola crops. “We have done intensive soil and tissue testing, and since using Bio-Sul, the efficiency on some of our client farms has really improved.”

Limoges adds that the majority of elemental sulphur in the Peace Region is applied in the fall because the application window is typically wider. “In our area, there are many other things farmers prefer to do in the fall, such as anhydrous ammonia application, harrowing or drainage projects. Some growers will apply elemental S to their whole farm upfront, while others, for example those using a three-year rotation, may apply the elemental sulphur in the fall prior to the areas planned for canola the following spring, and do that every year until the whole farm has been covered. That takes the S out of the canola fertilizer blend and breaks up the payments on the elemental S. And most importantly, products like Bio-Sul and other ES sources help growers address the need for S in long-term fertility and soil nutrient programs.”