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1. Improve nutrient soil retention and nutrient plant use efficiency for organic greenhouse crops;
2. Adjust the irrigation management and fertilisation under a recirculation system with or without treatment using wetlands;
3. Evaluate the efficiency of biochar on soil nutrient availability, plant productivity, plant disease tolerance, and soil biological activity;
4. Improve fruit yield as well as gustatory and nutritional attributes based on cultural management (intercrop, irrigation and nutrient availability);
5. Improve energy use efficiency by reaching yields similar to conventional growing system;
6. Recycle crop effluents in order to have zero nutrient emissions in the environment;
7. Evaluate the efficiency of biochar as a filtering medium to reduce the charge in nutrients (especially N, P, SO4 and Na) of greenhouse effluents and green house gas emission (N2O);
8. Evaluate the efficiency of different plant species (Phragmites australis, Typha latifola, Iris versicolor and fern) implanted in wetlands to reduce the charge in nutrients (especially N, P, SO4 and Na) of greenhouse effluents;
9. Evaluate the efficiency of different plant species (Phragmites australis, Typha latifola, Iris versicolor and fern) implanted in wetlands to reduce the presence of pathogens (Pythium spp., Fusarium spp., Clavibacter michiganensis and nematodes) in greenhouse effluents;
10. Evaluate the profitability of the proposed organic growing system compared to a conventional growing system.

The greenhouse industry is an important and growing segment of the Canadian agri-food industry, with a farm value of $2.3 billion (Statistic Canada, 2007). Although the main advantage offered by greenhouse production compared with other agricultural systems is the capacity to control growing conditions year-round, thus ensuring very high quality, yield, uniformity and steady supplies for distribution networks and consumers, greenhouse systems nonetheless account for significant emissions into the environment. Unlike the situation in hydroponics, fertilization decisions in soil-based organic systems involve taking the following aspects into account: storage, use efficiency, disease resistance and the well-being of soil microorganisms that help to 鈥渘ourish鈥� the plants. However, according to the soil physical/chemical properties, fertigation and irrigation management, we observed that organic growers may also contribute to important nutrient emissions into the ground water. This phenomenon is particularly evident on porous soils when nutrient supply and mineralization rate mismatch the plant water and nutrient needs. In order to reduce the environmental fingerprint of greenhouse production systems, the two main concerns for Canadian growers are (i) to have high efficient organic growing systems with yields similar to conventional growing systems and (ii) to reduce emissions of nutrient charged solutions into the environment by reusing crop effluents. Thus, objectives of the proposed project are to develop a more sustainable organic growing system for tomato based on 1) a better nutrient soil retention and nutrient plant use efficiency, 2) a better yield and consequently a better energy use efficiency, and 3) recycling of crop effluents through an efficient, cheap, low maintenance and biological processes such as constructed wetlands and passive bioreactors.

To achieve these objectives, an organic growing system will be compared to a conventional system in two compartments at Les Serres Nouvelles Cultures (Ste-Sophie, QC). Crop experiments will be performed over a three-year intercropping growing season of production (3 complete intercropped cycles; 6 crops). Conventional plants will be grown in coco fibers and irrigated with a conventional nutrient solution. Organic plants will be grown in raised bed containers filled with a certified organic coco fiber-based growing medium containing 35% of mineral soil and a minimum of 10% of compost. Organic fertilizers and amendments will be supplied weekly to fulfill plant nutrient requirements.  To improve soil physical, chemical and biological properties, biochar amendments will be studied in subplots in year 3. Two irrigation systems will be used: a drip tape at 15 cm (water only) and a sprinkler system at the soil surface (recycled water). Plants will be intercropped after 6 months to provide higher yield on an extended harvesting period. Greenhouse effluents will be collected separately for each treatment and will be re-circulated either directly or after being treated through wetlands.

Eight horizontal subsurface flow (HSSF) wetlands, each consisting of 5 cells in series, will be used: 4 wetlands to treat organic effluents and 4 wetlands to treat conventional effluents as a control. Biochar will be added to the filling material of 2 wetlands per type of effluent (2 replicates) to improve microorganism population and reduce greenhouse gas emissions. In each wetland, cells will be filled with a mix of gravel and organic amendment to provide a carbon source to the microbial population as COD of greenhouse effluents is a limiting factor for a high efficiency. Wetlands will be colonized with Typha latifola due to its tolerance to high salinity and sulfate content. Greenhouse gas (GHG) emissions (CO₂, N₂O and CH₄) from the wetlands will also be evaluated for life cycle assessment analysis. Total microbial activity, denitrifying microorganisms, sulfate reducing bacteria and the presence of pathogens will also be evaluated. In the greenhouse, fertilization, climate parameters, plant growth, fruit yield and fruit quality will be monitored.

More fundamental studies will be performed at the experimental greenhouse at Universit茅 Laval. The first series of trials will test the efficiency of four different plant types (Phragmites australis, Typha latifola, Iris versicolor and fern) to better colonize specific wetland cells receiving different salinity level and nutrient contents.  A second series of trials will be to assessed, through bioassays, the efficacy of different types of biochar to physically remove NO₃, P, SO₄ and Na from a charged greenhouse effluent. The third series of trials will test the efficiency of constructed wetlands with and without Biochar and implanted with Phragmites australis, Typha latifola, Iris versicolor and fern to reduce the presence of pathogens in recirculating systems. A fourth series of experiments will evaluate the beneficial effect of organic soil amended with biochar on plant growth, yield, fruit quality and plant disease and pest tolerance.

Results from that research project will provide cheap and efficient alternative solutions for Canadian organic, but also conventional, horticultural growers (field and greenhouse) to reduce their nutrient emissions into the environment. This study will also provide scientific information about the use of biochar as an environmental management tool, as little information is available, even though many assumptions have been made for C sequestration, nutrient value, soil quality in terms of physical, chemical and biological properties, and finally on the reduction of GHG emissions.

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  • Canadian Organic Science Conference. 2012
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  • Canadian Organic Science Conference. 2012

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