Calcium Products - Andrew Hoiberg, Ph.D.

Calcium Products - Andrew Hoiberg, Ph.D.

Andrew Hoiberg, Ph.D.

Andrew Hoiberg, Ph.D.

Soybean Nodules Adversely Affected by Low Soil pH

Soybean Harvest

Soybean nodules supply plant available nitrogen

Nodules on soybean roots are formed by a specific genus of soil-borne bacteria, Rhizobium, which form a symbiotic relationship with the plant. The nodules fix nitrogen from the atmosphere and transform it into plant available nitrogen, while the plant supplies necessary nutrients and energy for the bacteria to multiply and thrive.

Typically, nitrogen fixation via nodules supplies most of the nitrogen that a soybean crop needs during a given year and additional nitrogen applications are not advised as that can have a detrimental effect on nodules. If there is nitrogen available from applied fertilizer, the relationship between the nodules and the plants suffer, ultimately hindering the ability of the nodules to fix nitrogen. It’s a costly move for both growers and the plant-bacteria interaction.

Nodules hindered by low soil pH

Nodule formation and performance is hindered by soil pH below 5.7. Many fields in the Midwest have areas of the field, or wide expanses with values at or below this level. The acidification from nitrogen sources applied during corn rotations continue to drive pH values lower.

When ammonium sulfate (AMS) is used to supply sulfur for soybean crops, a two-headed monster is working against achieving maximum yield. First, nitrogen is being applied, which can hinder nodule formation and performance. Second, AMS is the most acidifying fertilizer used in agriculture today, and that acidity can further degrade nodules.

SO4 – a pH neutral sulfur source

SO4, which is pelletized gypsum, is a pH neutral sulfur source. Its natural solubility meets plant needs for sulfur throughout the growing season. An added benefit is the addition of calcium to replace that lost in the previous season’s harvest.

Increased soybean acres projected for 2017

Due to various agricultural economic metrics, 2017 appears to be on track for the largest soybean crop ever planted in the United States. The USDA predicts 85.5 million acres planted this year, 1.8 million more than last year.

Soybean and nodule health will be more important than ever with the predicted increase in acres planted. Ensure you are making the best decisions for crop health, including nodules, to maximize yields.

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Soil Testing Helps Inform Application Decisions

Soil Testing

Why soil test?

Soil testing is an important part of our philosophy at Calcium Products – without knowing the nutrient status of your soil, how are you to make informed decisions about what to apply to it?

Turf managers are normally good about soil testing, but if you haven’t been consistent about it or have been thinking about starting a soil testing program, now is the time to do so. With environmental regulations being administered in certain areas of the U.S., soil testing will help you maximize your fertilizer investment and make educated decisions on the best type of fertilizers to supply exactly what you need.

What a soil test measures

There are a wide variety of soil tests available that can help you gain insight into your nutrient status, soil type/texture, infiltration rates, water holding capacity, etc.

A basic soil test is likely to provide you with the following measurements:

  • - Soil pH
  • - Cation exchange capacity (CEC)
  • - Phosphorous
  • - Potassium
  • - Calcium
  • - Magnesium
  • - Lime requirement

Additional analyses that may be of interest depending on your location and situation might include:

  • - Soil texture
  • - Total soluble salts
  • - Sodium adsorption ratio (SAR)
  • - Sulfur
  • - Micronutrients

Nitrogen testing is typically not included in all sampling regimens due to its instability, making interpretation of the value difficult.

How to get started

Checking in with your state extension specialist to see what they recommend with regard to appropriate testing methods and preferred laboratories in your area is the best way to ensure you are testing all the right things for your situation.

Finding a lab you are comfortable with and that is regionally appropriate for you is important to maintain consistency and to build a historical database on which to inform decisions. The lab you choose will also offer recommendations on what nutrient levels to supply to bring them back into sufficiency range. You may double check with your state extension specialist to see if the laboratory recommendations are aligned with what they normally recommend.

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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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