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September 22, 2023

Sulfur Fertilizer Is a Natural Choice for Fall Application.

The trend toward fall fertilizer application continues to gain momentum among farmers in Canada and the Northern Plains States.

As acres increase and farmers seek to distribute the spring workload, sulfur is one nutrient that can be easily shifted to post-harvest application with minimal risk – and in the case of elemental sulfur – with added upside.

Freeing up input space during the busy season.

What’s driving the decision to apply certain fertilizers in the fall? The big one is time and resources. In the spring, there are a lot of inputs to get on in a relatively short window of time. Sprayer and applicator space is at a premium. The same goes for bin space.

With many farming operations cropping thousands (or tens of thousands of acres), the demand becomes more pronounced. Taking one nutrient off your plate can save a lot of time and worry.

Shifting elemental sulfur fertilizer to fall is an easy win.

In northern climates, fall is actually the best time to apply an elemental sulfur fertilizer. Broadcasting (or incorporating) will provide optimal results.

The reason? Degradable elemental sulfur products (ie. bentonite sulfur fertilizers) significantly benefit by sitting on or near the surface over winter.

The snowfall, moisture and elements help to break the pastilles down into fine particle sizes (1-180 microns). This speeds up the mechanical breakdown process and makes it easier for microorganisms to oxidize the elemental sulfur into plant-available sulfate in the spring.

As a rule of thumb, 30-40% of the elemental sulfur applied will be available to the crop over the growing season when you use a high-quality degradable sulfur product.

With degradable elemental sulfur, you don’t have to worry about losing sulfur nutrients due to leaching.

That’s because the microorganisms that oxidize sulfur to sulfate go dormant as soil temperatures drop. This means the sulfur will not be converted into sulfate until the spring – resulting in negligible loss.

What about ammonium sulfate?

Ammonium Sulfate (AMS)/sulfur fines are also commonly applied in the fall. Even though sulfate sulfur is mobile in the soil, loss due to leaching tends to be relatively low. With AMS, fall application also avoids known application challenges related to seed safety and the tendency for AMS to gum up seeding equipment in wet conditions.

The bigger concern is the nitrogen component. Nitrification continues until the soil temperature hits 0°C (32°F). Yet even this general guideline may not be as reliable as once thought.

A multi-region study published in the Canadian Journal of Soil Science (June 2019) reported that 47%–94% of fall-applied NH4-N was lost from the top 30 cm of soil before seeding in the next spring. Loss was higher in synthetic fertilizers such as AMS than in manure.

The authors (Chantigny et al.) concluded:

“Reactive N applied in the fall has high vulnerability to loss in cold and frozen soils, and strategies for improving N retention over the winter are required even in areas where prolonged freezing occurs.

Having readily available sulfur may outweigh the risks of nitrogen loss, particularly in crops with a high sulfur demand, such as canola. Applying both AMS and elemental sulfur (or a pre-packaged blend of both) is a common strategy.

Ready for spring

Whether you apply a degradable elemental sulfur (bentonite sulfur) fertilizer or ammonium sulfate (AMS), you will be getting a jump on the growing season. The two go hand-in-hand, as the AMS provides immediately available sulfate at the early crop stages, while the elemental sulfur delivers a reliable season-long sulfur source.

* “Chantigny et al. “A multi-region study reveals high overwinter loss of fall-applied reactive nitrogen in cold and frozen soils.” Canadian Journal of Soil Science, June 2019.

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