Gypsum Demonstration Project in Northeast WI

Glacierland R&D is currently partnering with 4 farms in northeast Wisconsin to demonstrate the use of gypsum (calcium sulfate dehydrate) as an agricultural soil amendment. The project will monitor changes in soil physical properties, crop response, and hold field days to share information. We are expanding the project to partner with a farm that has drain tile to apply gypsum and monitor changes in phosphorus concentrations in tile water.


Gypsum: What is it?

Gypsum’s use as a soil amendment has been documented as early as the 18th century. Overtime the agricultural use of gypsum declined due to the increasing cost of mining and transporting the product. Today, there are two main sources of gypsum used for agricultural applications; mined and synthetic. The primary source of synthetic gypsum is known as flue gas desulfurized (FGD) gypsum, which is produced as a by-product of the emission scrubbers used to reduce sulfur emissions in coal-fired power plants. An increasing number of electric power plants are using emission scrubbers to comply with air quality regulations, leading to a larger supply of FGD gypsum. Agronomic use of FGD gypsum has increased in the past 20 years due to the lower cost (compared to mined gypsum) and the increased supply and distribution of sources near agricultural areas.

Gypsum: Crop Production, Soil Structure, and Water Quality Benefits

Gypsum is approximately 23% calcium and 19% sulfur in its pure form. Gypsum applied at a rate of 1 ton/acre (2000 lbs.) will supply 320 lbs. of sulfur and 400 lbs. of calcium. Today, crops have less sulfur sources available to them since sulfur impurities were mostly removed from fertilizers. There has also been a decrease in atmospheric sulfur deposits since coal-fired power plants were required to install emission scrubbers. When these decreases are combined with the increased sulfur demand of high yielding crops, a sulfur deficiency is emerging in the Midwest. There is also a significant interaction between how crops utilize sulfur and nitrogen. Gypsum has been shown to significantly improve nitrogen use efficiency, suggesting that the crop cannot fully utilize nitrogen available in the soil if the sulfur requirements of the crop are not met.

There is a common misconception that gypsum is a liming agent. Different from calcium carbonate, gypsum does not change soil pH. However, gypsum is 200 times more soluble than calcium carbonate when applied to soil at a neutral pH. This allows the sulfur and calcium to move further through the soil profile into the rooting zone.

Gypsum is well known for its ability to improve soil structure. It increases the amount of stable soil aggregates; thereby increasing soil pore space, decreasing surface crusting, and increasing precipitation infiltration rates. Research suggests that it can often take several years of gypsum application before changes in soil physical properties are observed.

The improvements in soil structure and soil chemistry can also provide water quality benefits. Specifically, gypsum has been getting attention for research showing reductions in soluble phosphorus concentrations after one gypsum application. The mechanism for this decrease in soluble phosphorus is likely due to chemical changes in the soil after gypsum application. The calcium ions in the gypsum are able to precipitate phosphorus in the soil water into a less soluble form.

Recently, preliminary results were released from an Ohio State University study measuring soluble reactive phosphorus (SRP) levels in drain tile samples on seven farms in the Maumee River watershed. After one gypsum application (1 ton/acre), the treated plots showed an average of 55% reduction in SRP compared to the control plots.

srp-in-runoffProject History & Next Steps

We are partnering with four farms in northeast WI to demonstrate the use of gypsum as a soil amendment. Two of the farms had applications in the fall of 2014 and 2015. The other two farms had applications in the spring of 2015 & 2016. Spring or fall applications will both benefit the soil & crop, but weather and field conditions can limit the window of time for application. Soil tests are recommended prior to gypsum application to determine the best rate for the soil type and conditions. Three of the farms have an application rates of 1 ton per acre, which is the rate typically appropriate for soils in the area. The fourth farm has a rate of 1/2 ton per acre because of the lower cation exchange capacity of the soil. FGD gypsum has a consistency similar to flour, so it needs to be applied on low wind days. To reduce the risk of the product getting washed out, the gypsum should be applied 2-3 days ahead of any large rain events, allowing time to come in contact with and move down the soil profile.

 


 

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Contact Molly Meyers at mgc@glacierlandrcd.org or 920-680-6484 with any questions or for more information.

This project is supported by funding from the Great Lakes Commission and We Energies.

Additional Resources:

Gypsum as an Agricultural Amendment: General Use Guidelines
Gypsum for Agricultural Use: The State of the Science
Environmental Protection Agency: Agricultural Uses for FGD Gypsum