This study examines the feasibility of a small-scale farmer producing a high-quality soil amendment from wood waste products by using commercial style mushroom cultivation techniques. The byproducts of button mushroom cultivation have considerable value as an environmentally benign soil amendment; however, there is little information available about the value of spent substrate from oyster mushroom cultivation. This study outlines the expenses and labor involved with oyster mushroom cultivation, and it describes the levels of the available nutrients in rice straw and alder sawdust spent mushroom substrate.
Mushroom cultivation involves the introduction of a chosen fungus onto semi-sterile, nutrient-rich substrates. Altogether, the initial investment for small-scale mushroom cultivation was $1,843. After establishment costs, the expenses involved were substrate, containers (bags and jars) and cost of sterilization.
During the span of the trial, results were highly variable; seasonal changes like temperature and humidity radically affected yields. Dollar per hour return varied between $4 and $40 per hour (determined by net income divided by hours of labor). Pasteurized alder substrates produced fewer pounds of mushrooms per pound of labor. Pasteurized alder substrates produced fewer pounds of mushrooms per pound of substrate and generally had higher contamination rates than rice straw substrates.
After harvest, the spent rice straw and alder sawdust substrates were field weathered. We took compost samples once a month over a six-month period for each substrate. Both substrates were particularly high in available Ca and K and had even N-P-S ratios. The Alder substrate had higher total and available nitrogen.
Determine the feasibility of mushroom cultivation on the small farm by:
1) Documenting start-up costs
2) Documenting cost of supplies
3) Documenting yields and potential returns
Evaluate the nutritive value of spent mushroom substrates by:
1) Analysis of total nutrient composition immediately after harvest
2) Analysis of available nutrients in field-weathered spent mushroom substrate over a six-month period
Altogether, the initial investment for small-scale mushroom cultivation was $1,843. The single most important item for the starting mushroom grower is a laminar flow hood, which consists of a box outfitted with a High Efficiency Particulate Air (HEPA) filter. This box is charged with positive airflow, which is forced through the HEPA filter, creating a flow of sterile air in which mushroom spawn can be transferred. The laminar flow hood allows for the creation of a sterile environment in an otherwise “dirty” environment (any ambient mold spores or bacteria can spoil a substrate).
This project examined and used several methods of creating a suitable microclimate including:
1) Indoors, by creating microclimates within 40-gallon rubber totes.
2) In a low cost “hoop-house,” low-tech greenhouse using PVC as the structural unit as opposed to aluminum (well suited to cool weather climates).
3) Milking parlor growroom, a 1920s milking parlor retrofitted for fruiting mushrooms.
Of the environments used, the milking parlor growroom was the most effective and easiest to maintain. When growing in the milking parlor, pest exclusion was simplified, contaminated surfaces were easily sanitized and high relative humidity could be easily achieved by hosing down the concrete floor (evaporation simultaneously lowered temperature to an appropriate level and increased humidity). Because growroom expenses will vary from farm to farm, the cost of establishing a growroom is not considered in this study.
Other initial set-up costs include the purchase of a pressure cooker, propane burners, 44-gallon drums for pasteurizing bulk substrates, and 40-gallon rubber totes for the storage and incubation of bulk spawn (straw and sawdust bags). Included in the set-up cost was a bag sealer for the production of second-generation grain spawn.
OPERATIONAL EXPENSES AND POTENTIAL RETURNS
Once the initial investments in infrastructure are made, the cost of production for mushroom cultivation can be kept relatively low. By using inexpensive bags and farm wastes as substrate, the cost of production is confined mostly to sterilization expenses (propane) and containers (jars and bags).
Cost of sterilization was determined by recording the total number of hours that the propane burners were operated and applying that number to the cost of filling up a cylinder. The cost for pressure-cooking media and grain was $0.20 per hour and the cost of heating a 44-gallon drum for bulk substrates was $0.72 per hour (based upon $3 per gallon for propane).
Rice straw substrates generally yielded higher than sawdust and required less inoculums (grain spawn). In addition, less fuel was required to adequately kill weed fungi and bacteria (hot water bath versus steam pasteurization with sawdust).
The amount of labor necessary for mushroom production on either sawdust or straw substrates is about the same. As such, the yields (pounds of mushrooms produced) and inoculation rate are the major factors influencing the dollar per hour return.
Compost samples were taken approximately every 30 days and submitted for N-P-K plus micronutrient analysis. Over time the available nutrients remained at relatively high levels, even during record-breaking precipitation in November of 2006.
The sawdust substrate was more nutrient rich than rice straw, most likely due to high inoculation rates (nutrient rich rye spawn). When evaluated on the basis of total nutrients, the dry alder substrate had over 34,000 PPM (3%) nitrogen, with N-P-K ratio of ~20:1:2 (10:1:1 is desirable for uptake by plants). The same sample evaluated because of available nutrient had a ratio of ~4:1:2. Curing blocks in a shady location may help to balance the nitrogen ratio.
The rice straw substrate contained a smaller bank of immobilized nitrogen; however the pool of available nitrogen increased over the sampling period. In the rice straw substrate the N-P-K ratio was much more narrow when compared with alder substrates. Some sort of additional nitrogen-rich amendment would be required to bring nutrient levels into balance.
Both substrates were particularly rich in calcium and potassium. The potassium-rich substrates may be useful in helping with systemic pest resistance and preventing lodging in crop plants. Mushroom substrates may be useful in restoring potassium deplete soils.
The pH balance for alder and rice straw substrates were 4.7 and 5.6 respectively at the time they were placed in the field. Over the six months, these measures of pH changed only slightly and did not exhibit any linear relationship.
LITERARY RESEARCH AND OUTREACH
We primarily shared the results of our project through poster presentations. We first presented our poster at The Third International Medicinal Mushroom Conference in 2005 and the Washington Tilth Conferences in 2005 and 2006.
Research in alternative applications of spent mushroom substrate yielded several articles on the effect of mushroom polysaccharides on broiler chickens. These articles describe the effect of medicinal mushroom extracts on weight gain, bacterial populations in the cecum, coccidiosis, and immune response in young chickens. Because of this research, I performed an on-farm trial.
In this on-farm trial, pasture-raised broiler chickens were provided spent mushroom and the difference in death rate and carcass weights was recorded. While this trial has yielded some interesting and potentially significant data, the experimental design had a couple of discrepancies that keep the results from being definitive. These discrepancies have served as valuable lessons for future studies and direction for future work in poultry feedstuffs. Since performing this trial, I have continued to supplement my poultry with spent mushroom substrate; this has yielded several observations and will contribute to future experimental design. Anecdotal evidence suggests mushroom supplemented diet may reduce death rates.
Additionally, I gave a PowerPoint presentation on the life cycle of the mushroom and its cultivation at the Evergreen State College Organic Farm during the 2005 harvest Festival. In the spring of 2006, a group of students from the Practice of Sustainable Agriculture program visited the farm to see the integrated mushroom and poultry operation.
In fall of 2006, I led an interpretive mushroom walk for a group of students from an Evergreen class (a program called “Food,” focused on nutrition and food policy). I have also provided free consultations for several growers in the region.