Bentonite Sulfur Fertilizer: Your Fall Application Checklist
Finishing up the harvest usually means one thing for proactive growers: it’s time to start planning for next year’s crop.
Making a few strategic decisions in the Fall can set you up for success all year long. One of the smartest moves is optimizing your fall fertilizer program, particularly for nutrients like sulfur. Applying bentonite sulfur fertilizer in the Fall pays logistical dividends in the Spring, as well as agronomic benefits through the next growing season and beyond. By taking care of sulfur now, you’ll lighten your Spring workload and improve nutrient availability when your crops need it most.
This checklist outlines the key steps for a successful Fall sulfur fertilizer application. From evaluating your soil to choosing the right product and rate, use these pointers to ensure your elemental sulfur application delivers maximum benefit.
1. Check your soil profile
Before anything else, get the facts on your soil’s nutrient status. Soil testing may not always be the most reliable measurement, as it doesn’t capture the convertible organic reserves that remain in the soil. We recommend also testing the plant tissue in late Summer or Fall to reveal existing sulfur levels and any deficiencies. Why test in the Fall? It gives you a head start on addressing nutrient gaps and you’ll know exactly how much sulfur (and other nutrients) to add post-harvest. Sulfur can be hard to measure during the growing season because plants continually take it up, but after harvest a tissue test will show what’s left in the bank. If levels are lower than optimal, elemental sulfur is an excellent tool to build them up.
Pay particular attention to fields coming out of crops that have high sulfur removal. For instance, a big canola or alfalfa crop can strip significant sulfur from the soil. By testing, you might find deficiencies that weren’t apparent. Potential sulfur shortfalls can be managed cost-effectively with a fall elemental sulfur application. It’s much better to discover and fix a sulfur deficiency now than to be surprised by one in the middle of next season.
Ensure you’re looking at sulfate levels and organic matter (which can mineralize some sulfur) to gauge sulfur supply. Low sulfate in the top 0–24″ soil depth, coupled with low organic matter or coarse texture, often signals a need for added sulfur. If tissue tests from the last crop showed sulfur deficiency (e.g. low leaf S content or yellowing of new leaves), that’s another clue. Armed with these insights, you’re ready to take action.
Pro tip: You can even do soil tests in Winter if Fall was missed. Frozen ground is no barrier for sampling; the key is to know your starting point.
2. Select the best sulfur fertilizer for your crops
Not all sulfur fertilizers are created equal. When planning a Fall application, elemental sulfur, specifically bentonite sulfur pastilles, is usually the superior choice. Elemental sulfur offers a season-long release: it meets varying crop needs by providing sulfur steadily, which leads to higher nutrient uptake efficiency than one-time soluble applications.
This matches crop uptake patterns well, since crops need sulfur all season long, not just at the beginning. By contrast, sulfate forms like AMS or gypsum give an upfront blast of sulfur but are prone to leaching and may not persist until late-season. Elemental sulfur fits the bill for Fall application because it won’t wash away over Winter, and it stays put in the elemental insoluable form until soil microbes convert it in Spring. This means there is virtually no sulfur loss between your Fall application and the Spring uptake.
When choosing an elemental sulfur product, bentonite-clay sulfur pastilles (such as Keg River’s Keg90S™ or Keg85S™) are highly effective because the added bentonite clay helps the pastille disintegrate faster and more thoroughly. Once you apply these pastilles on the field, the clay absorbs moisture and swells, causing the sulfur to crack into tiny particles. Over the Winter, freeze/thaw cycles plus moisture continue breaking the pastilles apart. By Spring, a large surface area of sulfur particles is available for soil bacteria to do their work converting sulfur to sulfate. High-quality pastilles with premium bentonite will degrade more completely, yielding finer particles and thus faster oxidation come Spring.
Match the product to your crop needs: Consider the crops in your rotation and their sulfur requirements. For example, canola, canola-quality mustard, and other oilseeds have very high sulfur demand so they will benefit most from larger Fall applications of elemental sulfur and will readily use sulfate as it becomes available. Crops like wheat, barley, and corn have moderate sulfur needs; they’ll still respond to sulfur but may not need as high of a rate. Legumes (soybean, pulses) also need sulfur for protein formation, though often not as much as canola.
Don’t forget other nutrients: Fall is also a great time to address phosphorus (P) and potassium (K) needs, since those nutrients, like sulfur, are stable over winter. Many growers blend P and K with sulfur for fall spreading as a convenient way to build fertility and set the foundation for balanced nutrition next year in one pass. Elemental sulfur pairs well with these nutrients: all three are slow-moving in soil and benefit from early placement. If you have a composite blend, make sure the elemental sulfur pastilles are uniformly mixed and watch for any segregation issues.
3. Decide on rate and method of application
With your product chosen, the next question is “How much do I apply, and how do I apply it?” The optimal rate of elemental sulfur can depend on your current soil sulfur status, crop removal rates, and how many years you want the application to last. A common strategy is to apply a multi-year sulfur dose in one go. For example, some agronomists recommend applying enough bentonite sulfur to supply 2–3 years’ worth of sulfur on a field, all at once in the Fall. This might be on the order of 100–120 lbs/acre of product (which is ~90-108 lbs of actual S if using 90% analysis). That larger initial application “front-loads” the sulfur in your soil, which then oxidizes gradually over subsequent years. The benefit is that you ensure even the highest sulfur-demand crops have plenty to draw from, and you may not need to reapply sulfur every single year on that field. After such an initial build-up, you could switch to smaller maintenance applications in the following years, tailored to specific crop rotations and soil test results .
Of course, you don’t have to apply multiple years at once. Some farmers prefer an annual application approach, putting on a moderate rate (say 30–50 lbs/acre of product) every Fall so that there’s a fresh top-up each year. This can work well if you have diverse rotations or want to spread out costs yearly. Either approach can be effective; just ensure the amount of sulfur you apply replaces what your expected crop yields will remove and then some, to build your soil reserve.
Application method: Elemental sulfur is quite versatile in timing and placement. It can be broadcast on the soil surface or incorporated lightly. For Fall, broadcasting is usually recommended: simply spread the pastilles on harvested fields and let them lie on the surface over winter. Exposure to the elements actually benefits the breakdown as rain and snow directly on the pastilles will help them fracture. By Spring tillage or seeding time, many of the pastilles will have “melted” into the topsoil. If you practice no-till or minimum till, broadcasting works perfectly with no incorporation; the pastilles will still degrade as moisture wicks into them from the soil surface. If you plan to do any Spring field work like seedbed prep or cultivation, that will incidentally mix remaining sulfur particles into the soil. You can even apply sulfur on frozen ground or on snow in winter, and it will be in place by spring though avoid deep snow where the sulfur might runoff with snowmelt. Many northern farmers successfully apply on a light snow cover in late fall or Winter when fields are otherwise inaccessible.
Blending elemental sulfur with other granular fertilizers for a one-pass application is convenient. Just keep in mind pastilles are a different size/weight than typical NPK granules, so calibrate your spreader to achieve an even throw pattern. If unsure, applying sulfur alone might give the most uniform result.
One more tip on rate: Consider your crop rotation’s sulfur peaks. If you have a high-sulfur-demand crop next year, like canola or sunflower, target a robust rate this Fall to meet that need. If next year is a low sulfur user, maybe peas or soybeans, but the following year is canola, you can still apply now knowing much of the sulfur will carry into the second year. About 30-40% of elemental sulfur oxidizes per year under normal conditions, so a single Fall application can fuel crops for years if planned right. And don’t be afraid to overlap. If you apply every year, the overlapping sulfur ensures continuous multi-year availability and actually results in more efficient oxidation overall.
Think Ahead: Post-Application Monitoring
Even after you’ve applied your bentonite sulfur fertilizer, your job isn’t completely done. Successful fertilization is about feedback and adjustment, so plan to monitor the results. It’s smart to conduct post-application soil tests the following Spring or by early Summer to measure how sulfur levels have changed, and use that data to inform your next Fall application.
Did the Fall application raise your soil sulfate into the sufficient range? Are sulfur levels adequate at Spring seeding depth? Early tissue tests on the growing crop can also confirm if your sulfur nutrition is on point. For example, mid-season tissue tests could reveal sulfur-deficient plants by showing pale yellow upper leaves in a canola crop if the plant is not drawing sufficient sulfur from the soil. If tests indicate sulfur is still low or the crop shows deficiency symptoms, you might decide to supplement with a little in-crop sulfate fertilizer that season and increase your next Fall application. If levels are adequate, you’ll know to might maintain rate going forward. Over a few seasons, you’ll dial in the exact maintenance amount needed for your fields.
Also observe the physical aspects: when you scout your fields in Spring, look for signs of the sulfur pastilles’ breakdown. Often you’ll see only powdery remnants or nothing at all by Spring which is a good indication that they’ve dispersed properly. If you still see intact pastilles on the surface come Spring, it could mean very dry conditions slowed their breakdown or an application on frozen ground didn’t get moisture. In that case, you might adjust timing or ensure more moisture contact next time; even a light tillage pass or fall irrigation can help in arid regions.
Long-term tracking is valuable too. Keep records of yield and quality for crops in the years following sulfur application. Many growers notice improved yields, better grain protein content in cereals, or higher oil content in canola when sulfur nutrition is optimized. These benefits reinforce that your Fall sulfur checklist is paying off. By monitoring and recording these outcomes, you build a case for the ROI of fall fertilization.
Remember: what gets measured gets managed.
Plan for Spring Success
With fall applications now the norm for many progressive growers, it’s an ideal time to make elemental sulfur a cornerstone of your fertility program. And with Keg River’s premium bentonite sulfur fertilizer, you’ll be implementing a best-practice approach used by leading fertilizer dealers and agronomists across North America.
If you have questions or want personalized guidance, talk to your agronomist or reach out to a Keg River representative. We’re happy to help you fine-tune your fall fertilization strategy. Here’s to a well-prepared winter and an even better spring!
