A culture of Agaricus subrufescens (MP07) was obtained in 2007 and proven to produce mushrooms here in central Virginia outdoors on manure compost. Two cultures labeled as A. blazei (WC837-derived from ATCC accession 76739; and WC838- a multispore isolate from China) and one culture of A. subrufescens (MW17) were obtained from the Penn State University Collection for this project. These strains were grown on malt extract agar (MEA) medium. Culture growth on MEA for WC837, WC838, and MP07 was rapid and rhizomorphic as expected from this group. Growth of strain MW17 was slow and anemic on MEA. Transfer of MW17 to antibiotic media and corn meal agar, and amaranth-soy agar did not improve the growth rate or culture characteristics of the mycelium. All isolates were transferred to sterilized organic rye berries for spawn production. Strains WC837, WC838, and MP07 grew out rapidly and free of contamination. Strain MW17 grew very slowly on the grain and all but one bag of grain became contaminated with what appeared to be wet spot bacterial contamination. At this point strain MW17 was excluded from further study.
Fresh cow manure from pasture raised non-medicated cattle was obtained from a nearby farm and composted with local straw and gypsum. The approximately 15 yard compost pile was turned 3 times in 21 days and after the final turn was approximately 138F for four days. Commercial poultry manure composted with leaf debris was purchased after the initial heating and was piled for several days reaching approximately 120F before use.
Rectangular mushroom cultivation beds were built using a wooden frame as a mold. Each bed was 3’x6’x1’, holding 18cuft of manure. Beds that were to receive earthworms were built upon ¼” hardware cloth with edges bent up to exclude moles and voles. The cow manure (CM) compost beds were filled and the edges packed slightly to hold the bed shape as the mold was removed. Poultry manure (PC) compost beds were constructed in similar way with the addition of 1.5qt (approx 12lbs) of gypsum mixed throughout the beds. All beds were watered to about 75% moisture which reduced the temperature to an average of 76F across all beds. As the beds were filled with compost, rye grain spawn of the Agaricus strains were added and mixed throughout the compost at a rate of 18lbs per bed, approx. 1lb/cuft. To maintain moisture around the beds, straw was added in the paths between the beds and inoculated with Stropharia rugosa-annulata. Typar row covering was used to exclude insects and small animals from the beds. The Agaricus inoculum in the CM beds became contaminated with Trichoderma-green mold-as a result of low temperature and excessive moisture. Once these CM beds dried to approximately 70% moisture content they were inoculated with supplemented sawdust spawn containing Coprinus comatus, the Shaggy Mane mushroom.
Earthworms were added to several beds two weeks after inoculating the beds with Agaricus. One PC bed each containing MP07 and WC837 and a PC and CM control bed received 3lbs of red wiggler (Eisnea foetida) worms each.
Manure samples were sent to A&L Labs for testing before inoculation with fungi and at the end of the season to quantify N, P, K, S, Ca, Mg, Na, Al, B, Cu, Fe, Mn, and Zn.
Discussion with friends identified a concern about potential E. coli contamination using manures to cultivate edible mushrooms. Coliscan tests were obtained from Micrology Labs in Indiana. These tests were used to identify the presence of coliform bacteria and differentiate E. coli from other species by a color reaction in both CM and PC and the mushrooms harvested.
As the result of heavy rains and unseasonably cool temperatures soon after inoculation, all of the Agaricus grain spawn inoculated to CM became contaminated with Trichoderma green mold in the first two weeks. The center of the CM beds became saturated and anaerobic and the green mold predominated. The PC beds drained more readily and the spawn did not become contaminated. The cool weather did seem to slow mycelial growth for a couple of weeks initially. As the temperature warmed to mid-70F during the nights, the mycelium expanded rapidly changing the color of the compost to a lighter brown and smelling slightly of almond. This made mycelial expansion and colonization of the bed easy to observe. Of the three Agaricus strains, MP07 colonized the PC beds most rapidly, followed by WC837 and WC838, respectively. At 52 days after inoculation and several weeks of warm weather with nighttime temperature in the upper 70sF, primordial formation was evident on the edges of the two MP07-PC beds. Several caps formed in this initial flush and 4lbs harvested at the stage of the partial veil intact. Ten to twelve days later there was a second MP07 flush with 11.75 lbs. harvested from both beds. On this same day, primordia were present on the WC837-PC beds. Within 6 days less than 3lbs of WC837 were harvested. Mushrooms were given to several local chefs for sampling and feedback, eight pounds were sold for $24.00 per pound. The three chefs indicated the almond Portobello is an excellent culinary mushroom and would like to add it to their menus. The price per pound was average for high quality specialty mushrooms from a local distributor.
There were few earthworms but many cocoons in the bottom centers of the PC beds. Many introduced and native worms survived and thrived in the CM beds lined with hardware cloth. The near disappearance of earthworms from the PC beds is probably related to lower moisture content and lower food content of the compost than that of the CM beds.
Manure analyses of the PC beds shows the parameters for most minerals being similar and in lower quantities than the non-inoculated control bed. The exceptions include slightly lower levels of Calcium in the beds with mushrooms and earthworms. This might be attributed to Calcium metabolized by both species rather than just the fungi. In the WC838-PC bed there was triple the amount of Sulfur in the sample as in other beds. Although this strain produced mycelium and no mushrooms, this is most likely a sampling error in which an excessive amount of gypsum was present in the sampling location. The slightly acidic pH of the beds was consistent throughout the experiment averaging 6.8-6.9. Among the CM beds tested, CM non-inoculated control, CM with worms, and CM with Coprinus comatus mycelium there was no difference in the levels of the different minerals.
The MP07 and WC837 caps tested with Coliscan showed some indication of coliform bacteria but E. coli presence was not indicated in either sample. The CM beds inoculated with Coprinus comatus currently show strong mycelial growth and hold many earthworms.
Future work and Adoption of the method:
I will repeat this work in 2009 with some modifications. The mushroom strains used are labeled as different species, however Kerrigan(2005) indicated through DNA sequence analysis that species of Agaricus subrufescens, A. blazei, A. brasiliensis and A. rofutegulis are conspecific and should all be considered Agaricus subrufescens. Strains MP07 and WC837, merit further exploration as low input compost crops. Beds will be built and inoculation will occur earlier in the season so more than one or two flushes of mushrooms can be obtained. Beds will be smaller to reduce the possibility of anaerobic conditions, maximize the edge and stimulate larger mushroom fruitings. Further work will include methods for using smaller amounts of grain spawn by expanding and transferring mycelium directly in the bulk compost. Earthworms will not be introduced as they are expensive to obtain and do not seem to add to the measurable soil amendment value of the compost. Native earthworms will be encouraged to colonize the piles and protected with hardware cloth barriers.
Sequential inoculation of different fungi into the beds will indicate if there is possibility for more than one crop from composted manures before using it as a soil amendment. There is some research indicating enhanced crop growth and greater nutrient uptake by plants when saprophytic fungi are incorporated into planting bed soil. The CM beds inoculated with C. comatus will be used in vegetable planting beds to observe if a similar effect occurs and if mushrooms will form among plantings. In addition, several beds will be planted with leafy vegetables (eg. cucumbers, squash, tomatoes) and inoculated with A. subrufescens to observe intercropping effects and leaf mildew control potential with this fungus.
This work was included in a talk at a Small Family Farm Conference in Danville, Virginia in November 2008, and presented as part of a talk at the Virginia Biological Farming Conference in Richmond, Virginia in February of 2009. The work was described and discussed during an on-farm workshop at Sharondale Farm in March 2009.
The Almond Portobello mushroom (Agaricus subrufescens) was grown on composted poultry and leaf debris during summer outdoors in raised beds. The results of this work indicate that this could be an excellent short term crop for small farm compost management. The nutritional, medicinal and economic values of this mushroom are high and production methods to reduce production costs will continue to be developed at Sharondale Farm.