Recycled gypsum as a soil amendment

drywall pile for recycling drywall after the grinding process after removing the paper after pelletization
1. Clean drywall scrap is collected from construction sites. 2. The drywall is pulverized in a grinding machine. 3. The product is passed through a series of vibratory screens to remove the paper. 4. The resulting gypsum powder is pelletized to create an optimal product for field application.

Why Gypsum?

Gypsum (CaSO4), the primary component of drywall, contains calcium and sulfur—two nutrients that are required for healthy plant growth and development. Some crop species, such as potatoes and alfalfa have high calcium requirements, and may demonstrate improved growth with the addition of gypsum. Gypsum is an ideal amendment to support growth of plants with high calcium requirements because it has little effect on soil pH, compared to conventional calcium fertilizers, which greatly increase soil alkalinity. Gypsum has been shown to reduce erosion and improve water and nutrient infiltration in clay soils. In Western Montana, gypsum has also been successfully used to reclaim agricultural lands negatively affected by saline seeps.

How do I know if gypsum will benefit my crops?

soil test resultsA soil test must be taken on soil where recycled gypsum wallboard will be applied to determine soil type. This analysis will tell you the soil pH, and the amounts of phosphorus, calcium, magnesium, and zinc available for plants to use. The application rate for the gypsum wallboard is based on the amount of silt and clay that is typically present in the soil surface. You may download this list of soil, plant and water analytical laboratories for Montana agriculture.

How to collect soil for sampling

Please contact your soil testing lab for specific instructions. Here is the general procedure:

  1. Use a sampling probe or auger.
  2. Sample to plow depth (6-7 inches deep).
  3. Avoid unusual areas in the field.
  4. Take a minimum of five cores from different areas in the field and combine them into one composite sample.
  5. Take at least one composite sample per 5 acres.
  6. Place samples in labeled bag.
  7. Keep records of identification where samples were taken within fields.
  8. Fill out the forms provided by your soil testing service.

Recommended application methods

We process our gypsum product into small pellets, which can be applied via a typical fertilizer spreader. The results of your soil test will indicate the rate at which the product should be applied. In Montana, where agricultural soils tend to be more clayey than sandy, we have achieved satisfactory results with application rates of about 2 tons per acre. The product should be evenly mixed into the top four to twelve inches of soil at the recommended rate. For more information, please see Guidelines for the Application of Recycled Gypsum as a Soil Amendment in Western and Central Montana Agricultural Soils (Adobe PDF, 22KB).

Resources used for the above recommendations:

Drywall Recycling of Montana 2006 and 2007 field testing summary reports.

Soil Test Recommendations for Field, Vegetable, and Fruit Crops, Publication A 2809, University of Wisconsin Extension, K.A. Kelling, L.G. Bundy, S.M. Combs, and J.B. Peters.

Substituting Waste Gypsum Wallboard for Agricultural Gypsum: DNR Publication WA-607-04 rev.