COMPOST USERS FORUM
Tests in British Columbia show significant reductions in root rot disease and improved crop yields by addition of greenhouse compost.
Though there have been many advances in Integrated Pest Management (IPM) methods and resistant plant varieties, crop disease is an ongoing problem that continues to challenge growers in the greenhouse vegetable industry. Historically, here in British Columbia for example, diseases such as Fusarium crown rot in tomatoes have accounted for significant crop losses. New diseases continue to develop, creating more problems. Following a project that developed methods of producing high-quality compost (see "On-Site Composting of Greenhouse Crop Residuals" October, 2002 BioCycle), a study was undertaken to assess potential disease suppression capabilities of the compost.
The study included two main components - seedling growth tests and a yield test. In both cases, spores of the pathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici (FORL) were introduced into the growing medium and tomato plants were monitored for growth, health, and yield, depending on the test. A comparison was made between plants grown in conventional growing medium and medium amended or replaced with compost.
The compost was produced from a mixture of greenhouse plant waste, spent growing medium, and bark amendment, using a pilot-scale, invessel composting system and in some cases a laboratory-scale system. The exact composition was varied between batches - and included such feedstocks as tomato leaves, cull fruit, bark, sawdust and recycled compost coarse material. Materials were composted for about four weeks in the vessel with a peak temperature of about 65(deg)C, then cured for several months, and screened.
For this study, seeding into plugs made from compost, or rock wool plugs amended with compost, was compared to conventional rock wool plugs covered with vermiculite. Seedlings were evaluated after several weeks for plant height, root disease score and other parameters. Root disease score ranged from 1 to 5, 1 representing no signs of disease, and 5 representing a dead plant with typical symptoms of crown and root rot. Tests were conducted first in the University of British Columbia Plant Science Pathology Greenhouse, then moved to growth chambers for better environmental control.
Six individual seedling disease tests were conducted. The first two were "dry runs" to help establish the method. To compare treatments in terms of disease, a significant amount of disease must be created, at least in some of the plants. In one test, three plug types were compared: conventional rock wool with vermiculite covering, rock wool with compost covering, and compost with vermiculite covering. The first symptoms of crown and root rot began to appear four weeks after seeding, then developed so that after six and seven weeks, the disease was very apparent in some of the seedlings. Reduced disease symptoms were evident in compost-amended treatments, but no clear relationships with shoot height were apparent. Other tests clearly showed re
duced disease in seedlings treated with compost. The increased root disease in the rock wool inoculated treatment was significantly greater than in the noninoculated control, and amongst inoculated treatments, root disease in the compost-amended treatments was significantly lower than in the rock wool treatment.
Another growth chamber test compared rock wool plugs with compost-- amended plugs, where the seed was "sandwiched" between two layers of compost on top of a shortened rock wool plug. Several batches of compost were compared. The visual scoring of disease clearly showed reduced disease in seedlings treated with compost. The increased root disease in the rock wool inoculated treatment was significantly greater than in the noninoculated control, based on the root disease score. Again, amongst inoculated treatments, the root disease in the compost-amended treatments was significantly lower than in the rock wool treatment.
Impact Of Compost On Yields
The yield test, conducted in the UBC Horticulture Greenhouse, investigated the effect of adding compost to the conventional sawdust growing medium on yield, over a full growing season, and under severe disease pressure from fungus inoculation. The experimental set-up attempted to duplicate to the best extent possible the conditions in a typical commercial hydroponic greenhouse. Though the horticulture greenhouse is a modern glass research greenhouse, the climate and irrigation could not be controlled to the same extent. Nutrient solution was delivered from a manually mixed tank through drippers controlled by a timer; later in the season, feeding was controlled by a photo-sensitive controller. No artificial lighting was provided.
Among the two fungus-inoculated treatments, amendment with compost resulted in a 55 percent improvement in total marketable yield over the conventional treatment. This was primarily a result of premature death of a number of plants due to disease in the conventional treatment. When the yield per plant was calculated, taking into account one dead plant believed to be infected prior to starting the trial, the increase in yield was 74 percent, and statistically significant. Statistical analyses also showed that the 50 percent decrease in yield of the inoculated conventional treatment compared to the noninoculated control is significant. The ten percent decrease in yield for the noninoculated compost-amended treatment compared to the noninoculated conventional treatment was not statistically significant. The data also suggest a larger fruit size for compost-amended medium, but this difference was not statistically significant.
Conclusions From Comparative Tests
Significant reduction of crown and root rot disease caused by Fusarium oxysporum f. sp. radicis-lycopersici in susceptible tomatoes was achieved by addition of the greenhouse compost to seedling plugs or blocks, and by mixing with the sawdust growing medium. For propagation, the compost can be used as a rock wool plug covering, or a rock wool plug replacement. For growing, the compost can be mixed with sawdust growing medium; a mixture of 2:1 sawdust to compost by volume was shown to be effective. The reduction in disease resulted in 55 percent improved total yield over a full growing season under high disease pressure. In the absence of high disease pressure, addition of the compost to the growing medium did not have a significant effect on yield.
Based on the microbial counts, the compost likely increased the microbial population and bacteria to fungi ratio in the growing medium; this may have contributed to the suppressive effect, however determining the suppression mechanisms would require further study.
Positive effects were observed with several different batches of compost produced using the in-vessel composting systems; this encouraging result suggests that the disease suppression effects observed are reproducible using the appropriate materials and composting process. The results of this study will help provide greenhouse vegetable growers with alternative solutions to manage soil-borne disease.
[Sidebar]
Comparative trials with different batches of compost indicated that disease suppression effects are reproducible using varied feedstocks and composting processes.
[Author Affiliation]
W. Cheuk, K. V Lo, R. Branion, B. Fraser, R. Copeman and P. Jolliffe
[Author Affiliation]
William Cheuk, Dr. K. Victor Lo and Dr. Richard Branion are in the Chemical and Biological Engineering Department at the University of British Columbia, Vancouver. Bud Fraser is with Vision Envirotech International Company Ltd. in Vancouver, B.C. Dr. Robert Copeman and Dr. Peter Jolliffe are on the Faculty of Agricultural Sciences, Agroecology Program at the University of British Columbia, Vancouver.
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