The overall objective of this project was to examine if recycling spent oyster mushroom compost could help farmers manage plant-parasitic nematodes in the field. Six laboratory and two field trials were conducted for this project. In the four laboratory mushroom compost amendment trials, mushroom compost amended potting mix (peat moss or yard waste compost) planted with zucchini seedlings or without seedlings suppressed root-knot nematodes (Meloidogyne incognita) compared to unamended potting mix. However, the mushroom compost amendment did not suppress plant-parasitic nematodes if the potting mix did not contain sufficient organic matter (e.g. sand: soil mix at 1:1 v/v). Spent oyster mushroom compost collected from a local oyster mushroom grower was used to prepare mushroom compost water extract (MCWE) by soaking the compost into water at more than 25% brewed with air pump overnight. This reduced mobility of root-knot nematodes by more than 68.5% in the first MCWE trial. In the second MCWE trial, 10% MCWE reduced nematode mobility by 87.8%. However, the MCWE did not kill all the nematodes but rather paralyzed most of them. Based on these laboratory results, the next step in this project was to use oyster mushroom compost as basil seedling amendment in the transplant potting media and drenching MCWE to basil rhizosphere to provide post-plant nematode management. Two basil field trials were conducted at 1) Poamoho Experimental Station in Waialua (Trial I), and 2) at Magoon Teaching Facility in Manoa (Trial II), HI. Soil organic matter was used to enhance activities of oyster mushroom compost. Buckwheat was planted as a cover crop prior to basil planting in Trial I, whereas yard waste compost mulch was used as surface organic mulch in Trial II. Unfortunately, both mushroom amendment and MCWE drenching did not suppress numbers of plant-parasitic nematode in both field trials. However, soil health improved in the mushroom compost treatments based on nematode community analysis conducted by quantifying the free-living nematodes. In Trial I, regardless of cover cropping, mushroom amendment and drenching had increased abundance of bacterial feeding nematodes, enrichment index (EI) and reduced channel index (CI), indicating an enhancement of the bacteria decomposition pathway, and thus, a more enriched soil food web. Similar soil food web enrichment effect was observed toward the end of Trial II. In addition, mushroom amendment alone also increased abundance of omnivorous nematodes and structure index (SI) when used in conjunction with yard waste compost mulch, indicating a more structured soil food web compared to no mushroom amendment. In this trial, nematode richness was also higher in mushroom amended compared to non-amended plots. Drenching with MCWE did not affect free-living nematodes in Trial II. Despite the obvious improvement of soil health by mushroom compost treatments, basil yield was not improved by these treatments, in part due to downy mildew infection in both trials. Mushroom amendment and MCWE drenching increased basil plant growth but not yield in Trial I. In Trial II, mushroom amendment and MCWE drenching did not improve basil growth and yield, but the yard waste compost mulch did.
Three extension articles, one student symposium poster, and three symposium/conference presentations were generated. A student M.S. thesis focused on this project is at completion stage. Two high school students adopted this project as their high school science fair project for two consecutive years. A website was created to update the public about our new findings. Two display booths were exhibited at the University of Hawaii College of Tropical Agriculture and Human Resources (CTAHR) Annual Organic Field Day and Centre of Rural Agricultural Training and Entrepreneurship (CRATE) Field Day.
Plant-parasitic nematodes are prevalent pests in nearly all vegetable crops in tropical climates in Hawaii (Schmitt and Sipes, 1998). Many farmers are looking for alternative methods to chemical approaches for managing nematodes in the soil. Oka (2010) had reviewed the effects of a series of organic amendments including animal and green manures, compost, and nematode-antagonistic plants on suppressing plant-parasitic nematodes. A type of compost that is known to secrete toxic compounds against nematodes but has not received enough attention is the oyster mushroom compost. Gray oyster (Pleurotus ostreatus) and King oyster mushrooms (Ali’i) (Pleurotus eryngii) are two common commercially produced oyster mushrooms in Hawaii. Pleurotus ostreatus is known to exude a toxin from the fungal hyphae, known as trans-2-decenedioic acid (Kwok, 1992). This toxin paralyzes the nematodes on contact, which allows the hyphae to move into position to colonize and digest the nematode. Studies on the effects of oyster mushroom on nematodes have been predominantly in vitro. Palizi et al. (2009) demonstrated the use of mushroom compost with sugar beets (Beta vulgaris) in the field by directly incorporating the mushroom compost into soil at 3% (w/w). The mushroom compost suppressed more than 85% of sugar beet cyst nematode (Heterodera schachtii) cysts. Although direct incorporation of the mushroom substrate into the soil could ensure direct contact of the mushroom mycelia with the root system, the amendment rate needed for nematode suppression using this approach could be unfeasible in the field- or even at the garden-scale if an ample supply of the mushroom compost is not available.
This project evaluated the optimum amendment rates and drenching concentrations. Utilizing the results from the laboratory, two field experiments were conducted using mushroom compost amendment and the MCWE drenching for plant-parasitic nematodes. Soil health was also evaluated with nematode community analysis. This project explored different approaches to use mushroom compost for the suppression of root-knot nematodes (Meloidogyne incognita) through: 1) direct incorporation of the mushroom compost amendment into the soil before crop planting, 2) drenching mushroom compost water extract into the root system after crop planting, and 3) amending mushroom compost into the growth media of transplant trays. Several factors might affect the applicability and efficacy of nematode suppressive effects of mushroom compost. These include mushroom species, mushroom compost amendment rate, concentration of mushroom compost water extracts, and local availability of the compost.
The overall goal of this project is to explore the potential of spent oyster mushroom compost for managing M. incognita on basil. Specific objectives were to:
- determine the amendment rate of spent Pleurotus compost in organic potting medium against M. incognita;
- establish a mushroom compost water extract (MCWE) concentration for incognita suppression; and
- demonstrate a mushroom compost based technology for pre- and post-plant nematode management on basil in the field.
Laboratory experiments were conducted to evaluate mushroom compost amendment rates of two Pleurotus species, and concentrations of mushroom compost water extract against root-knot nematode (Meloidogyne incognita). Two field experiments were conducted at two locations to evaluate the benefits of mushroom compost amendment and MCWE drenching.
Objective 1: Four laboratory trials were conducted using Cone-tainers (soil tubes) to evaluate amendment effect
Cone I: Cone-tainers (soil tubes) containing 100- cm3 of Hawaiian Earth Product yard waste compost mulch were amended with Pleurotus ostreatus mushroom amendment at 50, 33, or 0% (v/v). Media was inoculated with 200 Meloidogyne incognita juveniles and were exposed to different concentrations of spent Pleurotus ostreatus mushroom compost for 1, 4, 7, or 30 days prior to extracting the nematodes from the soil to check for nematode viability.
Cone II: Two sets of soil tubes were established similar to Cone I, one set was amended with compost of P. ostreatus whereas another was amended with P. eryngii. Concentrations of both species were 50, 33, 2, 1, and 0% (v/v). A zucchini seedling was planted into each cone at time of amendment to evaluate nematode penetration into the root. M. incognita juveniles were inoculated 14 days after germination. Plant shoot and root weight was measured 11 days after nematode inoculation. Roots were stained with acid fuchsin and nematodes were extracted from the media using elutriation and centrifugal floatation methods.
Cone III: Methods from Cone-tainer II were repeated for cone-tainer III with the exception of using peat moss as the growing medium instead of Hawaiian Earth Product yard waste compost. Concentrations of mushroom compost for both species were 50, 33, 2, 1, and 0% (v/v)
Cone IV: Methods were repeated for cone-tainer IV with the exception of the media and the species tested. Pleurotus ostreatus was the only species evaluated in cone-tainer IV. A 1:1 ratio of peat moss and sterile sand was used and then amended with mushroom compost at 50, 33, 2, 1, and 0% (v/v).
Objective 2: Two laboratory trials evaluated mushroom compost water extract (MCWE)
MCWE I: The first laboratory trial was conducted by incubating M. incognita juveniles in MCWE aerated for 24 hours at concentrations of 0, 25, 33, and 50% over five days. The experiments were conducted in 60 mm × 15 mm petri dishes.
MCWE II: The second MCWE trial using 0.25 ml micro-dishes with concentrations of 50, 25, 10, and 0% MCWE.
Objective 3: Field Trials for pre- and post-plant nematode management on basil.
Trial I: A basil field trial was conducted at Poamoho Experiment Station, Wailua, Oahu, HI between August 2014 and January 2015. The experiment was a 2×2×2 (cover crop × amendment × drenching) split-split plot design with six replications arranged in randomized complete block. Each sub-plot was 2.4 × 0.6 m2. Half of these plots were planted with a cover crop (C), buckwheat (Fagopyrum esculentum), at seeding rate of 56 kg/ha for four weeks and then soil incorporated. Basil seedlings were transplanted at 30-cm spacing within a row, i.e. eight plants per plot. Half of the basil seedlings received 50 % (w/w) mushroom amendment (A) and the other half not. Beginning at four weeks after transplanting, half of the plants were drenched (D) with 25 % (w/w) MCWE at a tw0-month interval and the other half were not drenched. Spent mushroom compost was obtained from Hamakua Heritage Farm (Laupahoehoe, HI). Before each drenching treatment, the 25% (w/w) MCWE was aerated for 24 hours and drenched at 100 ml per plant at two-month interval. The basil crop was grown for six months. Height, chlorophyll readings, and yield were harvested and were recorded every three weeks.
Trial II: Trial II was conducted at the Magoon Experimental Station, Manoa, HI. Trial II was slightly modified from Trial I where yard waste compost mulch (M) was used as surface organic mulch instead of growing buckwheat (Fagopyrum esculentum) cover crop as additional organic inputs. This was a 2×2×2 (M×A×D) split-split plot experiment with four replications. Each subplot was 2.4 × 0.3 m2. Height, chlorophyll readings, and yield were recorded every three weeks. Plant-parasitic and free-living nematodes were extracted from the soil and counted at two-month interval. Nematode community analysis was performed to evaluate for soil health.
Objective 1: Laboratory trials for mushroom compost amendment effect
Four laboratory experiments were conducted to determine the mushroom amendment effect on root-knot nematodes using 100-cm3 cone-tainers (soil tube). In Trial I, M. incognita juveniles were incubated in different concentrations of Pleurotus ostreatus mushroom amendment for 1, 4, 7, or 30 days. The treatments of 30 days of incubation had the least amount of nematodes but were not statistically different from seven days. In Trial II, regardless of the amendment rate, the mushroom compost was not able to suppress root penetration of root-knot nematodes, but at 1% or higher, the mushroom amendment suppressed nematodes in the media. Similar nematode suppression was observed for both oyster mushroom species tested. Amendment rate at 2% or greater, regardless of mushroom species, produced higher root weight than unamended. In Trial III, root-knot nematode abundance in the media was lower in 2, 33, and 50% than 1% and unamended control. In Trial IV, 1:1 ratio of peat moss and sterile sand was used. Penetration of root-knot nematodes into the roots were lower in 1 and 33% concentration of amendment compared to 2, 50, and unamended control.
Objective 2: Laboratory trials for mushroom compost water extract (MCWE) effect
The results from the first laboratory trial showed that mobility of nematodes was suppressed by MCWE regardless of concentration when incubated more than two days compared to the water control. However, after washing the nematodes in water, most nematodes regained mobility, suggesting that the MCWE only had a nematostatic and not nematicidal effect. The second MCWE trial using micro-dishes showed that MCWE suppressed mobility of M. incognita by 87.8% at concentration of as low as 10% compared to the water control. Thus, 10% MCWE was determined as the concentration needed to suppress M. incognita.
Objective 3: Field trials for pre- and post-plant nematode management on basil
Two basil field trials were conducted to evaluate mushroom amendment and MCWE on plant-parasitic and free-living nematodes using the rates determined from the laboratory trials. Unfortunately, both mushroom amendment and MCWE drenching did not suppress numbers of plant-parasitic nematode in both field trials. However, mushroom compost treatment improved soil health based on nematode community analysis conducted by quantifying the free-living nematodes. In Trial I, mushroom amendment and drenching regardless of cover cropping, increased abundance of bacterial feeding nematodes, enrichment index (EI), and reduced channel index (CI), indicating an enhancement of the bacteria decomposition pathway, and thus, a more enriched soil food web. Similar soil food web enrichment effect was observed toward the end of Trial II. In addition, mushroom amendment also increased abundance of omnivorous nematodes and structure index (SI) when used in conjunction with yard waste compost mulch, indicating a more structured soil food web compared to no mushroom amendment. In this trial, nematode richness was also higher in mushroom amended vs non-amended plots, whereas drenching with MCWE did not affect free-living nematodes in Trial II. Despite the obvious improvement of soil health by mushroom compost treatments, basil yield was not improved by these treatments, in part due to interference from heavy downy mildew infection on basil in both trials.
Educational & Outreach Activities
- Ching, S. and K.-H. Wang. 2015. Use of oyster mushroom compost for nematode management. H?nai‘Ai Newsletter August 2015. http://www.ctahr.hawaii.edu/sustainag/news/articles/V24-MushroomCompostPoster.pdf
- Ching, S. and K.-H. Wang. 2014. Mushroom compost to battle against nematode pests on vegetable crops. H?nai‘Ai Newsletter August 2014. http://www.ctahr.hawaii.edu/sustainag/news/articles/V20-Ching-Wang-MushroomCompost.pdf
- Wang, K.-H. and S. Ching. 2014. Rhizosphere inoculum and amendment. H?nai‘Ai Newsletter March 2014. http://www.ctahr.hawaii.edu/sustainag/news/articles/V19-Wang-RhizoInoculum.pdf
- Ching, S. and K.-H. Wang. Effects on Oyster Mushroom Compost Waste on Soil and Plant Health in Plant-Parasitic Nematode Infested Soils. 54th Society of Nematologists Annual, East Lansing, MI. July 2015. http://www.ctahr.hawaii.edu/WangKH/Downloads/SON-Ching2015.pdf
- Ching, S., and K.-H. Wang. Evaluating the potential of oyster mushroom compost waste for plant-parasitic nematode management. International Conference of Nematology, Cape Town, South Africa. May, 2014. http://www.ctahr.hawaii.edu/WangKH/Downloads/ChingMushroomCompost.pdf
- Ching, S., K.-H. Wang, and B.S. Sipes. 2014. Evaluating the potential of oyster mushroom compost waste for plant-parasitic nematode management. CTAHR Student Research Symposium, Honolulu, Hawaii (Abstract #33).
- Wang, K –H. and S. Ching. Center of Rural Agriculture Training and Entrepreneurship (CRATE) Day. Poamoho Research Station. June 27, 2015. Attendance ~30 participants.
- Sugano, J., S. Fukuda, K.-H. Wang, T. Radovich, A. *Pant, J. Uyeda. Soil health workshops with NRCS. Poamoho Experiment Station, Waialua, HI. February 7, 2015 Attendance: ~50 participants.
- Wang, K.-H. and S. Ching. Organic Field Day. Waimanalo Research Station, July 26, 2014. Attendance ~200 participants.
High School Science Fair Project:
- Au, V. H.-S., and Liang, Y. 2014. The effect of oyster mushroom compost on nematode-infested soil. Hawaii High School Science Fair Project (3rd place at the Honolulu District Science Fair; Best of Category award in Environmental Sciences at the Hawaii State Science Fair; win recognition from the Hawaii Agricultural Research Center (as a result, the students traveled to Los Angeles to observe the National High School Science Fair Competition).
- Au, V. H.-S., and Liang, Y. 2015. Go green mushrooms: A field analysis of Pleurotus ostreatus compost effects on soil health. Hawaii High School Science Fair Project (2nd place for Environmental Sciences Category, Dupont Pioneer Award).
Flickr page: Oyster Mushroom Compost Project. https://www.flickr.com/gp/129290180@N08/vpT25d
The results from our replicated laboratory trials confirmed the myth that spent oyster mushroom compost suppresses plant-parasitic nematodes by reducing their mobility in the soil. The effect is nematostatic rather than nematicidal, which is similar to many conventional nematicides. However, our field trials demonstrated that using oyster mushroom compost at a practical application scale such as that described in this project would not be sufficient to achieve plant-parasitic nematode suppressive effect. On the other hand, our results clearly demonstrated mushroom amendment or MCWE drenching treatments could improve soil health by enriching the soil food web and even improving soil food web structure if conducted in a field with a history of minimal till or when use in conjunction with yard waste compost as mulch. Plants would be more tolerant of plant-parasitic nematodes damage if the plant health is improved by amending with mushroom compost. This would be a useful tool for small-scale organic farmers.
More than 200 visitors visited the CTAHR Organic Field Day at Waimanalo on July 26, 2014 where we hosted a display booth on the use of mushroom compost for nematode management. Most of the visitors were small-scale farmers located on Windward side of Oahu or home gardeners. A survey conducted at the workshop showed that 87.5 % participants were highly interested in growing their own oyster mushrooms using coffee ground. Most participants gave a positive reaction to this project and think that it is a useful tool and will pass on to others. Participants also look forward to learn about how this project benefits the farmers in the community.
About 30 new farmers from the University of Hawaii new farmers training program, GoFarm Hawaii, attended the Center of Rural Agriculture Training and Entrepreneurship (CRATE) Field Day at the Poamoho Research Station on June 27, 2015. These are mostly farmers interested in organic farming. In a scale of 1-5, they rated an average of 4.6 on willing to adopt the application of mushroom compost waste into their farming practice if the compost is readily available.
This project was especially supported by the largest oyster mushroom producer in Hawaii, Robert Stanga at Hamakua Heritage Farms, LLC, in Laupahoehoe, Hawaii. The company donated mushroom compost substrate for us to conduct the field and laboratory trials. They appreciated the publications we produced online and are sharing that with their clients, visitors and school kids (http://hamakuamushrooms.com/).
Overall, we generated three extension articles in H?nai‘Ai (an online quarterly newsletter for Sustainable and Organic Agriculture Program in Hawaii), two student symposium presentations, and two scientific conference presentations at the International Congress of Nematology in South Africa and the 54th Annual Society of Nematologists meeting in East Lansing, MI, and attracted two high school students from McKinley High School, Oahu to adopt this project as their high school science fair project for two consecutive years. They have won awards for their district science fair competition and won 2nd place in their Environmental Sciences at the 58th Annual Hawaii State Science and Engineering Fair. The graduate student, Ching, presented the results in poster format at the CTAHR Student Symposium and won third prize for the poster competition. We also created a website for the public to view results from this project (http://www.ctahr.hawaii.edu/WangKH/mushroom-compost.html).
This project did not plan for economic analysis of a technology but targeted to evaluate an alternative nematode management approach that is environmentally friendly, suitable for organic farming, and helpful in recycling farm waste (spent oyster mushroom compost). Under the field evaluation conducted during this project, the use of oyster mushroom compost as seedling amendment or post-plant soil drenching was not benefiting the basil crop production due to complication from heavy infestation of downy mildew. Our field trials demonstrated that use of mushroom compost amendment or MCWE drenching were consistently improving soil health. We hypothesize that if the basil can be grown in farms that are not infested by downy mildew, the improvement of soil health could lead to better basil yield as indicated in the greater plant height in the mushroom treated plots in Trial I. The current seedling amendment rate tested would only require approximately one ton/acre of mushroom compost, a more feasible practice than recommending farmers to use 10-20 tons/acre of regular compost to improve plant health. If the use of oyster mushroom compost as amendment or MCWE drenching were to be taken place in organic farms that generally would have higher organic matter in the soil, the only additional inputs would be the mushroom compost treatment. Availability and prices of spent mushroom compost vary by location. Currently the cost of mushroom compost waste at cubic yard is unclear, but a company we work with inoculates a commercial soil inoculum to their compost and the product is sold for $10/lb. The result from this project demonstrated that using the spent oyster mushroom compost waste without additional soil inoculum could make the recycle of mushroom compost waste at a more economical rate for the farmers.
The key farmer participant in this project is Robert Stanga from Hamakua Heritage Farm that produces edible mushroom in Hawaii. His company provided all the spent oyster mushroom compost for our project. We updated our findings to the company whenever we generated a new publication or presentation. Although selling mushroom compost waste is not a priority for the company, they conduct farm tours to share their knowledge about mushroom culture to students, teachers, home gardeners, tourists, and occasionally farmers. They appreciate our findings and were excited to share it with their clients that have the potential to use his product. One organic basil farmer that signed up to conduct field trial at his farm ran into complications and was not able to facilitate and participate in the field-testing of this project. However, we conducted field days to share our results with new farmers that are interested in organic farming. In a scale of 1-5, they rated an average of 4.6 on willing to adopt the application of mushroom compost waste into their farming practice if the compost is available.
Areas needing additional study
While the laboratory results provide promising evidence of suppressing root-knot nematodes using oyster mushroom compost as seedling media amendment or water extract drenching (two-month interval), our field results did not provide significant effects. Future research should examine the effect of more frequent MCWE drenching against the plant-parasitic nematodes. More trials need to be conducted to evaluate the basil yield and growth without the interference from downy mildew or using a more resistant variety. Other sources for organic matter might have different results. We have evaluated a cover crop of buckwheat and yard waste compost mulch, but there is potential for other combinations of organic matter. Cover cropping also has the potential to improve soil health and manage plant-parasitic nematodes. Certain cover crops, such as sunn hemp (Crotalaria juncea) or marigold (Tagetes sp.), have nematicidal toxins that will release toxins and kill nematodes.