Mulching of vegetable crops in the South provides an effective way to maintain soil and plant health by reducing soil-borne pathogens, weed pressure, and soil moisture loss while increasing organic matter over time. However, the cost of mulching decreases early season cash outlay, potentially lowering seasonal and overall farm profits due to the increase cost in materials and labor if yields aren’t increased. Farmers in the Southeastern U.S. need a way to offset the cost of mulching through either an increase in overall farm sales or a decrease in cost of straw and labor.
By incorporating mushrooms like Stropharia rugosoannulata and Hypsigus ulminarus into the mulch, farmers have the potential to further increase soil fertility and plant health while increasing revenue across the Southeast as both of these species can be grown in temperate and subtropic climates.
Mushroom mulches would also rapidly build soil because the enzymes the mushrooms exude for digestion would increase the decomposition rate of debris into organic matter, micro, and macro nutrients. This research project will provide tangible, Southeastern specific results as to whether and by how much mushroom mulch intercropping increases vegetable yields while bringing in new, diversified income to small farmers. This research is critical in providing data for Southeastern U.S. growing conditions, to determine potential vegetable yield increases, sustainability benefits, and potential additional revenue from mushroom crop. While the benefits of mulch are known, mushroom crops may be a way to reduce financial risk of mulch by increasing diversified revenue streams. Intercropping mushrooms with vegetables has some anecdotal evidence of providing these benefits.
We will measure relative costs of set-up and maintenance of various mushroom mulches, comparative yields between mulched and non-mulched vegetable cash crops, and soil moisture and weed pressure in the various treatments.
Henosis Planting and Innoculation Succession
We decided that the best action to ensure that mycelium (fungus) would run along the mulch and have a chance of fruiting was to plant broad leaf vegetables first, spread straw mulch and sawdust (a common substrate material in oysters production) and then inoculate the beds with Wine Cap in the path ways and elm oyster (Hypsizygus ulmarius ) in the vegetable beds.
Following the steps in Paul Stamet’s book “Mycelium Running”, we layered water saturated poplar sawdust, mushroom spawn (80% sawdust and 20% coffee silver back) and a layer of straw mulch on top (approximately 18 bales) 1.5 bales/30 ft row. We watered the sawdust in a watering trough and spread it around the vegetables. We then added two 5 pound bags of sawdust spawn on top of the saw dust layer, added more water, and a layer of wet straw mulch.
We used the same process for the six control beds minus the mushroom spawn. All the beds were approximately 4 – 6 inches deep with mulch and sub-layers.
We then watered each bed by hand every day for two weeks approximately 10 minutes/bed to ensure that the fungus would establish itself and not dry out. Afterwards, we relied on drip tape on the top of the mulch to maintain adequate moisture level. We also added an additional bed outside the hoop house to increase our level of control over the fungal analysis. The same method was applied; sawdust, spawn, and straw but it was open to the elements.
From Plot A and Plot B (the control) we didn’t see any evidence of an increase in production and or revenue from mushroom production. Weighing the vegetables and visually inspecting the beds for mycelial growth did not lead to the conclusion of higher production of vegetables or a potential added revenue stream of wine cap or elm oyster mushrooms as the substrate and watering mechanism was ill suited for adequate mycelial (fungal) growth. Just using elm oyster spawn, we did not see any adequate fungal growth in the bed exposed to the elements either.
The following chart is a side by side of vegetable yields between Plot A (Inoculated plot) and Plot B (Control):
The vegetables harvest for spring 18′ saw Plot B, the control, producing more vegetables than Plot A except for cabbage. Plot B produced 48% more beets than Plot A and 55% more Kale. There was no real discrepancy in cabbage production.
The vegetable harvest for the summer saw 23% more production in sweet potatoes from Plot B over Plot A. Plot A produced more squash 51% more squash than Plot B.
Tomato production was not of any significance.
We did not see a significant turn out in any crop production due to poor germination from excessive heat and poor watering practices trying to increase fungal growth thru overhead watering techniques. This watering technique proved to be ill effective in producing mushrooms or vegetables. The cabbage rotted and the beets and kale never reached full maturity.
Plot A: The initial soil test did not provide a great baseline to work with as the soil was very fertile receiving an over all grade of 84 or “Optimal” by Cornell’s Soil Health Standards. However, there was improvement from the spring to fall season. The biggest improvement was in aggregate stability with a value raise from 38.8 to 69.6, ACE soil Protein Index, Soil Respiration and extractable Potassium and extractable phosphorus*
There were decreases in organic matter from 6 – 4.9 and active carbon from 980 to 927.
Comparing the initial test of Plot A and B there were only slight differences in overall health. The main differences were in organic stability, ACE Protein Index, Extractable Phosophorus, and Extractable Potassium
Plot B: There were improvements to Plot B’s overall soil health with the highest increase in aggregate stability from 45.5 to 74.2. There were decreases in Active Carbon (1009 – 927) and Extractable Potassium 394 – 232.
Comparing the soil activity over time between Plot A and Plot B we did see slightly better increase in overall soil health from A over B. The biggest changes coming in the form of ACE Soil Protein Index in the positive and a significant decrease in potassium of Plot B over Plot A which showed an increase of 3.7.
|Soil Attribute||Plot A Point Change||Plot B Point Change||Point Difference|
ACE Soil Protein Index
|Active Carbon||– 53||– 82||29|
*The build up of extractable phosphorus in open air systems could be seen as a potential environmental hazard if soil runoff should ensue and pollute a body of water.
Further studies need to be conducted as we did not see a significant change in soil health outside of potassium loss and due to the lack of fungal growth we cannot infer that it was due to mycelium.
Labor and Materials
Labor Applying Mulch and Inoculating
Mulching for one row 10 inches thick of water soaked* straw takes approximately 45 minutes. It takes approximately 30 minutes to apply 2 (5.5 pound) bags of spawn on a 30′ x 40″ bed. Total prep for one bed by hand takes 1.15 hours to mulch and inoculate.
Educational & Outreach Activities
Due to the lack of fungal growth and establishing best managment practices (BMP’s) for creating mushroom beds outreach was at a minimum until we could adequately establish growing parameters. Farmer’s time is limited and we felt that bringing people out to see a lack of positive progress was overly zealous when a simple report would provide adequate understanding of the progress.
We did give several one-on-one personal tours to farmers and told them about the progress and participated in the Middle Tennessee Farmer’s meeting to tell them about our work. No materials were made until we could establish better (BMP) and have more success in fungal maturation.
Establishing best management practices for fungal beds is key to the success of growing mushrooms in this type of system. Simply following the loose instructions in Paul Stamet's book "Mycelium Running" did not prove to be an effective way to grow Hypsizygus ulmarius mycelium on sawdust and straw mulch, let alone mushroom fruiting bodies. Having discussed my results with another mushroom company, Field and Forrest, whom had done their own research on using Elm Oyster they too concluded that this type of fungus was not suitable for outdoor production in this manner but suggested that we use another mushroom in the Pleurotus genus as they hypothesized that it would have the vigor to establish itself as it did not yield in our study both in and out of the controlled environment.
We were also given better instructions on how to maintain proper moisture through irrigation. Instead of using drip tape which has a limited percolation surface area, and staked spray nozzles which creates disease on vegetables, it was said that we use soaker hoses. It was also discovered that there are two types of sawdust: wet sawdust (check on industry verbiage) which comes straight from a felled tree, and kiln fired sawdust from mills making lumber. In this study we were using sawdust from kiln-fired wood that was extremely hydrophobic even after having been soaked in a trough. This material proved to be immensely hard to keep moist and would not be cost effective to hand water or soak to maintain low overhead cost.
Establishing fungal beds and creating a system of maintenance is key to the success of growing mushrooms in this type of system. Elm oyster mushrooms are not a good choice for this type of system.
Root vegetables (beets) are not easy to sow in this mulch systems due to the burden of moving mulch and not being able to use a seeder.
Watering overhead was not adequate in maintaining moisture levels in the beds and rotted the vegetables. Soaker hoses as mentioned by Field and Forest in their study may prove to be more effective in maintaining proper moisture in the mushroom mulch.
None of the beds saw any clear difference in production output.