Calcium Products - Andrew Hoiberg, Ph.D.
Calcium Product 98G

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Andrew Hoiberg, Ph.D.

Andrew Hoiberg, Ph.D.

Rescuing Sulfur Deficiency with Topdress Application of SO4

SO4 vs No Sulfur

Photo above: 2016 sulfur trial on corn in Kanawha, Iowa at the ISU Northern Research Farm. SO4 applied at 150 lbs/acre (left) and no sulfur applied (right). SO4 application resulted in a 30 bu/acre increase compared to no sulfur.

Expect Sulfur Deficiency

With seemingly endless rainfall this spring, we can expect widespread sulfur deficiency as corn continues to emerge. The problem is that sulfate is easily leached from where the young corn roots need it in wet years. Sulfur deficiency shows up in the youngest leaves of the plant, and consists of green and yellow stripes in the leaves. Many confuse nitrogen deficiency with sulfur deficiency, and the most likely scenario is that it’s sulfur and not nitrogen since most growers typically put out more than enough nitrogen to meet crop needs.

To compound this problem, wet springs often mean that sulfur applications were skipped or postponed in lieu of getting seed in the ground during short windows of opportunity. Further, most sulfur sources that can quickly supply sulfur to the crop via topdress application have high burn potential.

Topdress SO4

SO4 is the perfect sulfur source for any application scenario, but the ability to topdress SO4 without any concern over crop burn makes it stand out against other sources.

Research conducted at Iowa State University with SO4 has shown that green-up will occur in less than 1 week with topdress applications up to V6.

SO4 Application Rates

How much sulfur you need to apply for your crop depends on your soil type. In coarse textured soils with low organic matter content, shoot for about 25 lbs of sulfur per acre (150 lbs/acre of SO4); for finer textured soils with 3% organic matter or more, application rates closer to 17 lbs of sulfur per acre should suffice (100 lbs/acre of SO4).

It’s hard to accurately predict where and when sulfur deficiency will occur, but you can save your yield potential and correct in-season sulfur deficiency with topdress applications of SO4.

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Natural vs. Synthetic Gypsum

Synthetic Gypsum

What is Gypsum?
Gypsum is a mineral that has been used in agriculture for a long time. Its chemical name is calcium sulfate dihydrate (CaSO4 • 2H2O). It provides a sulfur source in the plant available form, sulfate, and provides calcium – both essential nutrients in crop production.

SO4 is naturally mined gypsum
SO4 is pelletized from gypsum that is naturally mined in northwest Iowa. Gypsum deposits were left behind when inland seas that used to cover Iowa dried up and receded.

Synthetic gypsum is a byproduct of burning coal
In contrast, synthetic gypsum (photo above) is a byproduct of burning coal. This source is commonly referred to as synthetic or flue gas desulfurized (FGD) gypsum. Power plants have ‘scrubbers’ that control emissions from their flue stacks. The process in its entirety is called flue gas desulfurization.

In short, these scrubbers filter by forcing sulfur dioxide and calcium carbonate (limestone) to react with one another, which creates calcium sulfite (CaSO3). Most power plants also use an additional step called ‘forced oxidation,’ whereby the calcium sulfite is oxidized to calcium sulfate, or synthetic gypsum. The resulting moist material is either landfilled or used in various industries around the U.S. – wallboard for instance. 

Challenges with synthetic gypsum
There are a few challenges with synthetic gypsum worth considering:
1. Coal contains heavy metals, which are generally isolated in the scrubbing process but occasionally can end up in the synthetic gypsum, raising obvious concerns about agricultural applications.
2. In bulk form, the material contains high moisture levels, making it difficult to spread and manage. As a result, recommended application rates are in the 1,000+ lbs/A range, which can create imbalance in the soil. These rates lack scientific evidence supporting their use in Midwest agriculture.
3. The purity of synthetic gypsum is only as good as the starting feedstock (limestone) and the system that produces it, creating highly variable chemical characteristics. Because of its synthetic/by-product nature, it will never be registered for organic use.

Synthetic gypsum is difficult and expensive to pelletize due to its fine particle size and requires the use of specialized binders and additives. This results in slow breakdown and activity in the field.

In summary, natural gypsum is mined from the earth while synthetic gypsum is a byproduct of burning coal. SO4 is pelletized, natural gypsum. It’s consistent pellet size allows it to blended and applied with other dry fertilizers.

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Localized Dry Spot

Localized Dry Spot

What is localized dry spot?

With an unusually hot start to the late spring/summer season, localized dry spot (LDS) is showing up earlier and more vigorously than normal. LDS shows up as somewhat randomized, dry looking areas of turf. It is generally seen on sand-based greens, but can occur on other turfs that have been heavily topdressed with sand over the years. Sand-based soil has greater propensity for hydrophobic conditions, which is the main sign of LDS.

What causes localized dry spot?
The deeper cause, beyond sand-based soils, are believed to be organic acids and residue that coat the soil or sand particles. These organic compounds are not completely understood, but are the result of typical decomposition of leaf tissue, roots, fungal biomass and organic soil amendments included in the original root zone mix. These compounds tend to have a hydrophobic nature and once they have coated soil particles, lead to LDS. Combine this hydrophobicity with root growth stoppage in heat and soils that already have low moisture holding capacity, and the problem can become bad in a hurry.

How to manage localized dry spot
While there is plentiful research into the causes and potential areas that could be managed differently to delay or correct LDS, the primary management technique has been and continues to be the use of wetting agents or surfactants to allow water to re-infiltrate areas that develop hydrophobicity.

There are several different chemical groups in the wetting agent and surfactant world, but the goal of all of these products is to lower the surface tension of water so it can infiltrate the hydrophobic soil. It pays to do your homework on the types of products available in the market to determine which one will provide you with the best result. Some of the older chemistries can cause phytotoxic effects on plants, so make sure you fully understand what you’ve got before spraying it on your greens.

Be prepared
Unfortunately, there doesn’t exist today a ‘silver bullet’ to cure LDS. The best strategy is to incorporate existing knowledge into new construction and for existing problems, to know when it’s coming and be prepared with a wetting agent or surfactant strategy to minimize the damage and interruption in play. Be sure to know what your local extension has to say about LDS management in your specific area.

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Can 98G and SO4 be Applied on Frozen Ground?

Frozen Ground

We are often asked about applying our products on snow-covered or frozen ground. While it may seem intuitive that products should not be applied to frozen ground, in general, applications can be made during late fall or winter and have similar considerations as other times of the year, such as water and ground conditions.

When determining if conditions are adequate to apply SO4 and 98G, keep these considerations in mind.

Potential for water runoff

Water influences movement of surface applied inputs. When water has potential to runoff and not infiltrate, then perhaps applications should be delayed.

Late fall and early winter before the ground is completely frozen can be a good time to make applications. As long as there’s not a substantial amount of snow on the ground (less than 6 inches), applications of 98G and SO4 can still be made. If snow comes early, there’s potential that it will slowly melt and start breaking down the product, which will help disperse the particles of the pellets and make them more effective come spring.

Even if the ground is completely frozen, applications can be made before too much snow accumulates. An extremely wet spring with multiple, heavy rain events can lead to water, and thus, product runoff and off-target effects, so paying attention to long range forecasting can help inform application decisions.

Slow snow melt and ground thaw is the best case scenario for products applied on frozen ground. Even if there is some runoff, it’s not likely that all of the product will be taken from where it was applied.

Soil tillage

Heavy or primary tillage (moldboard or chisel plow, ripper) is not a recommended practice after application of 98G or SO4. Application should be delayed until after these tillage practices have already occurred, due to non-uniform depth of application and the likelihood that the pellets will be placed too deep in the soil profile to affect meaningful pH adjustment.

If ground is not completely frozen, then there’s still a chance for the product to start working its way into the ground. SO4 should always be surface applied and left to release its nutrients from the surface, so if some tillage is expected after the application, it may be wise to delay application until spring after ground work has been completed. 98G can be incorporated via surface preparation, so the same considerations do not apply to both products in this case – incorporation can also reduce runoff potential for 98G.

Field slope

Slope of the field should also be considered; relatively flat ground is less susceptible to runoff events and will have more leeway with late fall and winter applications.

To summarize, frozen ground applications are acceptable if snowpack and slope are minimal – however, the risk of excess water in the spring and significant runoff are always present.

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