What Are the Best Sulfur Fertilizers for Organic Crops?
Organic producers have exciting new options to boost yield and quality
Sulfur is an essential nutrient for plant growth that is gaining more focus every year as a critical factor for successful production – with the use of a sulfur fertilizer to optimize results now viewed as a “must do” across many different types of farms.
But what many may not realize is that sulfur fertilizer is not only important for conventional crop production but equally – if not more so – for organic production. It is vital for everything from cash crops such as canola, soybeans and cereals, to a wide assortment of greenhouse-grown staple crops, vegetables and more.
“Whether you are growing organic in the field or the greenhouse, the right sulfur fertilizer approach can go a long way to ensuring you get the best yield and quality,” says Brooke Bateman of Keg River. “It can make a big difference to every stage of plant growth ensuring your crop reaches its full potential.”
Organic field crop production
Sulfur is particularly important in organic production because it helps to optimize soil conditions which are that much more critical. After all, there is less reliance on other inputs.
The need to ensure adequate sulfur is especially vital in field crop production because conditions such as weather and external pressures are unpredictable and out of the growers’ control. Making sure to optimally apply sulfur fertilizer serves as a valuable insurance policy to make sure your crops will have the best chance of success, no matter what challenges nature throws at you.
Greenhouse/horticulture production
In a greenhouse environment, the conditions are controlled but the expectations for results and profitability thresholds can be higher. Getting sulfur right is essential to maximize the soil and infrastructure resources of the greenhouse to get the most out of the plants.
The rising importance of sulfur
Although sulfur has traditionally been considered a secondary nutrient, it is now becoming recognized as the “fourth macronutrient” – joining alongside nitrogen, phosphorous and potassium as a vital element for optimizing both field or greenhouse strategies.
The challenge for organic production is that not all types of sulfur fertilizer qualify for use in organic systems. Ammonium sulfate (AMS), potassium sulfate and ammonium thiosulfate are all off-limits. However, the good news today is there are now excellent new options available, including next-generation elemental sulfur fertilizer products.
Bentonite sulfur fertilizers (elemental sulfur)
You won’t find a more economical, higher analysis, season-long source of sulfur for agricultural use. Its two primary ingredients are organic: elemental sulfur and bentonite clay. In most cases, the only additional requirement necessary to achieve OMRI certification is the use of an organic dust suppressant.
Top examples include Keg River Organics* Keg 90S (0-0-0-90S) and Keg River Organics* Keg85S (0-0-0-85S) – both of which are approved for use in organic production by the Organic Materials Review Institue (OMRI). These options are easy to handle and provide reliable steady release for optimal season-long sulfur.
Plant availability can be accelerated somewhat through a fall application. The winter freeze/thaw cycle will help disintegrate the pastilles into smaller sulfur particles, for quicker breakdown in the spring, once the soil microbes ‘awaken’ from dormancy.
With bentonite sulfur, it is wise to choose an established manufacturer with a proven track record. Bentonite sulfurs made with premium clays and manufacturing processes will offer significantly superior performance. Clay is an invaluable dispersal mechanism. When a good quality clay is activated by moisture, it fractures pastilles into smaller sulfur particles, thereby increasing the surface area available for oxidation.
A premium clay will cause the sulfur to degrade into much finer particles (under 200 microns) for faster, more complete, more consistent conversion to sulfate. This ensures crops get the maximum nutritional benefit. Products made with enhanced dust control measures will be safer and cleaner to handle.
Sulfur analysis: 90% or 85%
Application options: Broadcast (preferred), seed row, banded
Advantages:
- Highest sulfur analysis, season-long sulfur source
- The slow-release mechanism minimizes the risk of leaching
- High analysis, season-long requires fewer passes
- Can be used for soil amendment programs to lower pH
Sulfate of Potash (SOP) and Gypsum
Among additional options that qualify for use in organic production is the combination of Sulfate of Potash (SOP) and Gypsum, which has been used to improve soil quality for over 250 years. It contains approximately 17% sulfur – as readily available sulfate. SOP and gypsum are commonly used as sulfur sources, only where soils or cropping call for it.
Sulfur analysis: ≈17%
Advantages:
- Immediately plant available
- Affordable sulfur source
- Source of calcium
- Soil amendment to increase organic content
Choosing the right solution
When making your sulfur fertilizer decision, there are several factors to consider:
- Is your soil sulfur deficient – and to what extent?
- What crops are you growing?
- How will you be applying the fertilizer and when?
- Do you want an immediately plant-available fertilizer, a slow-release product or both?
The best place to start is to speak with your fertilizer retailer or agronomist. If you’re not sure about the sulfur content across your fields, soil and tissue testing are highly recommended.
As an organic grower, or business serving organic customers, take the time to see if the fertilizer manufacturer’s commitment to responsibly-produced products and core values align with your own.
By considering all of these factors you’re sure to make a decision that’s right for your crops and the environment.
