Turf - Using Spent Mushroom Soil as an Ammendment

We ge a lot of questions on the use of mushroom soil on turf. The following are guidelines for selecting a mushroom soil from Penn State University.

Selecting a Spent Mushroom Soil (SMS) product - some guidelines to follow

Although many of the ingredients that go into SMS products are similar, not all products are alike. Quality of SMS can vary depending on the ingredients, how it is produced, and how it is treated after it comes out of the mushroom production houses. Because of potential quality differences among products, it is important to have some basis for determining suitability for use on turf. Ideally, the product you intend to use has been field tested and used successfully by other turf managers. Using a SMS product with a proven track record can take some of the guess work out of the selection process provided that it is consistent from batch to batch.
Whether you are using a field-tested SMS or one that has never been used on turf, be sure to obtain a sample of the product prior to use and examine it for undesirable objects and peculiar or offensive odors. If the producer does not have an analysis of chemical and physical properties, submit a representative sample to a laboratory that will conduct appropriate tests and provide recommendations that you can understand. Penn State's Agricultural Analytical Services Laboratory offers a compost testing service with several options for analysis of SMS products. Information on the compost testing program and other soil testing programs can be accessed at http://www.aasl.psu.edu/.

Some basic guidelines for evaluating the suitability of SMS products for use on turf follows.
General appearance: The appearance of fresh SMS is similar to peat, with a light brown color and a light, fibrous texture. Weathered SMS products should resemble dark topsoil and have a loose, crumbly structure. All SMS products to be used on turf should be free of large stones, plastic, and other objectionable objects.

Particle size: The size of SMS particles can vary depending on how it is produced. For use in surface applications on athletic fields, lawns, or golf course fairways, the SMS should pass through a 1/2 inch screen (or be of similar size). Composts with slightly larger particles can be used as soil amendments if thoroughly tilled into the soil prior to seeding or sodding.
Odor: A good quality SMS product should have an 'earthy' aroma. It should not emit peculiar or offensive odors such as those associated sulfur or rotten eggs. Also, it should not emit a strong ammonia odor. Peculiar odors may be an indication that the product is not mature (not fully composted). Immature SMS may have adverse effects on turf and should not be used.

Weed seeds: If the SMS product has been properly composted and stored, weed seed contamination will not be a problem. On rare occasions, SMS products are stored for long periods and neglected. In such cases, weed plants can begin to grow in the piles. If these weeds are not controlled immediately they can deposit seeds in the product.

Although a few weed seeds do not necessarily preclude the use of a SMS product as a soil amendment for turf, products containing large amounts of weed seeds are unacceptable. If possible, inspect the production site to make sure that weeds are not growing in and around the SMS piles.

Moisture content: The moisture content of a SMS product is important where uniform application and good mixing with soil is desired. Products with moisture contents between 30 and 50% are usually ideal for handling, surface applications, and soil incorporation. Wet products (greater than 60% moisture content) tend to form clumps and do not spread evenly when applied to turf surfaces. Tilling wet material into soil may result in poor mixing with soil and uneven turf establishment. Wet SMS is heavy and difficult to handle.

A quick field test that you can use to determine suitable water content of SMS is to squeeze the product in the palm of your hand and watch for water oozing from the product. If water drips from the SMS upon squeezing, then the product may be too wet, and further drying should improve product handling. If the SMS remains together when you release your grip and no water drips from the product, it probably has suitable water content for spreading and mixing with soil.

Organic matter and ash content: When using SMS as an organic matter supplement, keep in mind that not all of the product is organic matter. Spent mushroom substrate products typically contain between 40 and 60% organic matter on a dry weight basis. Organic matter content can be determined by a lab test. The most common procedure employed by laboratories, "loss on ignition", considers everything that is combustible as organic matter.

Some test labs report a value called 'ash content'. Ash is the mineral matter that remains after the SMS sample has been subjected to extremely high temperatures in a furnace. Assuming that everything burned-off in the furnace is organic matter, the percentage of ash in the sample can be subtracted from 100 to provide an estimate of percent organic matter. For example, an ash content of 40% indicates that there is an estimated 60% organic matter in the sample.
Carbon to nitrogen ratio: The amount of carbon (C) relative to the amount of nitrogen (N) in a SMS product is an important indicator of nitrogen availability. The carbon to nitrogen (C:N) ratio of a product should be 30:1 or below. If above 35:1, soil microorganisms can immobilize nitrogen, making it unavailable to the turf. Most SMS products have C:N ratios well below 30:1.

Nutrients: When compared with fertilizers, SMS products generally contain low amounts of plant nutrients. Whereas a small amount of quick-release nitrogen (ammonium) is present in SMS, most nitrogen is in the organic form and is slowly available to turf. Test results of SMS products typically indicate 1.5 to 3% total nitrogen on a dry weight basis. Other nutrients found in SMS include phosphorus (0.5 to 2.0 %, reported as P2O5), potassium (1.0 to 3.0%, reported as K2O), calcium (3 to 6%), and magnesium (0.4 to 1.0%).

Typically, significant amounts of SMS must be applied to supply all or most of the turf's nutrient requirements. In some cases, this can be achieved for short durations (8 to 10 weeks) with surface applications of ¼ to ½ inch of SMS, aerated into the soil surface. In many cases, a 1 or 2 inch layer of SMS tilled 4 to 6 inches into soil can supply all of the nutrients necessary for turf growth and development for an entire year and possibly longer.

pH: The pH of most SMS products is between 6.0 and 8.0, a range favorable for turf root growth. On rare occasion, a product may fall outside of this range. The pH of organic amendments may be detrimental to turf when very high (greater than 8.5) or very low (less than 5.5). Extremes in pH may result in reduced availability of some plant nutrients and/or aluminum toxicity problems. Fortunately, most soils are buffered against rapid and drastic changes in pH and even organic amendments with extremes in pH may not alter the overall soil pH a great deal. To be on the safe side, however, try using products with a pH between 6.0 and 8.0.

Soluble salts: Soluble salts may be higher in SMS products than in other types of organic amendments. Whereas, excess soluble salts can cause turf injury, research conducted at Penn State shows that good quality SMS products do not contain salt levels high enough to damage turf. If you have questions regarding the soluble salt content of a particular SMS product and how safe it is to use on turf, send the product to a soil test lab that performs soluble salts analyses on composts.

Penn State's Agricultural Analytical Services Lab and other laboratories measure soluble salt content in SMS by saturating the sample with water, extracting the solution from the sample, and determining salt content by measuring the electrical conductivity of the solution. The higher the electrical conductivity of the solution, the higher is the salt content of the SMS. Soluble salt content is most often reported in units of electrical conductivity (mmhos/cm or dS/m).

From "USING SPENT MUSHROOM SUBSTRATE (MUSHROOM SOIL) AS A SOIL AMENDMENT TO IMPROVE TURF" Department of Crop and Soil Sciences - Cooperative Extension, Penn State University http://turfgrassmanagement.psu.edu/spentmushroomsubstrate.cfm