Gravel, V., Dorais, M., Dey, D. and Vandenberg, G. 2015. Fish effluents promote root growth and suppress fungal diseases in tomato transplants. Can. J. Plant Sci. 95: 427–436. Aquaculture systems generate large amounts of wastes which may constitute a beneficial amendment for horticultural crop in terms of nutrients, plant growth promoter and disease suppressiveness. This study aimed to determine (1) the nutrient value of rainbow trout farming effluents coming from two feed regimes and (2) the plant growth and disease suppressiveness effects of those fish farming effluents on tomato transplants. The effluent sludge from Skretting Orient™ (SO) had a higher content of P (38 vs. 32 mg L−1), K (23 vs. 11 mg L−1), N (19 vs. to 11 mg NO3 L−1; 186 vs. 123 mg NH4 L−1), and a higher NO3:NH4 ratio (1:9 vs. 1:13) compared with the Martin Classic (MC), while MC was richer in Mg (42 vs. 24 mg L−1) and Ca (217 vs. 169 mg L−1). For the first trial, a stimulating effect of the fish effluent was observed on plant height, leaf area and root dry biomass, while only the root biomass was increased during the second trial. Fish sludge was rich in microorganisms (97 and 142 µg fluorescein h−1 mL−1 for SO and MC, respectively) and their ability to suppress Pythium ultimum Trow and Fusarium oxysporum f.sp. lycopersici (Sacc.) Snyder & Hansen was observed. Both crude fish effluents reduced in vitro mycelial growth of P. ultimum and F. oxysporum, by 100 and 32%, respectively, while MC effluents showed a higher inhibition against F. oxysporum. When fish effluents were sterilized by filtration or autoclaving, lower in vitro inhibition of P. ultimum and F. oxysporum was observed. Mixed fish effluents reduced tomato plant root colonization by P. ultimum (by up to 5.7-fold) and F. oxysporum (by up to 2.1-fold). These results showed that fish effluent can be used as soil amendments to promote plant growth and increase soil suppressiveness, which in turn can prevent soil-borne diseases.

Gravel, V., Dorais, M. and Ménard, C. 2013. Organic potted plants amended with biochar: its effect on growth and Pythium colonization. Can. J. Plant Sci. 93: 1217–1227. Even though the benefits from the use of charcoal in agriculture have been known for a long time, little biochar is utilized in agriculture. Therefore, we hypothesized that biochar amendment to an organic potting soil improves plant growth without promoting plant root pathogens such as Pythium ultimum. Growth of sweet pepper, lettuce, basil, geranium and coriander grown in an organic potting soil containing a commercially available biochar (1:1 vol:vol) was compared with an unamended potting soil. Macronutrients (NPK) were supplied through application of an organic liquid fertilizer three times a week via injection irrigation. The effect of biochar amendment on P. ultimum colonization and infection was also evaluated in a sub-sample. No effect of the biochar amendment on growth was observed for sweet pepper and geranium. On a dry weight basis, coriander shoot growth was 45% greater in the biochar-amended potting soil, while a decrease of 44% in shoot biomass was observed for lettuce. The negative growth impact of biochar was not related to a phytotoxicity effect as water extract from biochar did not affect seed germination. For Pythium-inoculated plants, root colonization by the pathogen was higher for all crops in potting soil amended with biochar, except for coriander. However, despite the fact that biochar offered a good environment for P. ultimum development as shown by a higher root colonization rate, no visible signs of damage to the root system or to plant development were observed. Soil respiration was lower when biochar was present in the growing medium, which could be related to a lower root biomass and the biochar-specific properties on greenhouse gases rather than to a reduction in the potting media biological activity. In conclusion, replacement of an important proportion of organic growing media with biochar may be beneficial in terms of plant growth and CO2 emission, but may also offer a good environment for Pythium ultimum development.