The use of artificial wetlands to treat greenhouse effluents

Untreated greenhouse effluents or leak solution constitute a major environmental burden because their nitrate and phosphate concentrations may induce eutrophication. Artificial wetlands may offer a low cost alternative treatment of greenhouse effluents and consequently improve the sustainability of greenhouse growing systems. The objectives of this study were to 1) characterize the efficiency of different types of wetland to reduce ion content of greenhouse tomato effluent, and 2) improve the wetland efficiency by adding carbon of 0-800 mg L-1 sucrose. Experiments were conducted at Laval University where 30 pilot scale horizontal subsurface flow artificial wetlands (0.81 m3) were built. Two types of aquatic macrophytes, Pragmites australis and Typha latifolia, and a control group without plants were tested. The hydraulic retention time was 10 days. During the study, EC of the greenhouse effluent ranged between 1.5 to 5.5 mS cm-1, while 0 to 800 mg L-1 of sucrose was provided to improve the biological activity of the wetland. The macro- and micro-elements, the greenhouse gases (CH4, CO2, N2O) and the population of bacteria were measured for each unit. At commercial scale, two vertical subsurface wetlands (43.2 m3) were installed at Ste-Sophie Québec, on the production site of Les Serres Nouvelles Cultures (Sagami). According to our results, 50-90% of nitrate (NO3-) and 40-100% of phosphate (PO43-) were removed from the effluent. At Laval University, artificial wetlands with Typha latifolia were more efficient than wetlands with Phragmites australis or without plants. Addition of sucrose increased wetlands’ microbial population and consequently reduced the mineral content of the wastewater, but increased significantly the emission of greenhouse gases. Results will further be discussed in terms of the best wetland design to treat greenhouse effluents, but also in terms of the environmental impact

Organic Nitrogen Uptake and Assimilation in Cucumis sativus Using Position-Specific Labeling and Compound-Specific Isotope Analysis

Organic nitrogen is now considered a significant source of N for plants. Although organic management practices increase soil organic C and N content, the importance of organic N as a source of crop N under organic farming management systems is still poorly understood. While dual-labeled (13C and 15N) molecule methods have been developed to study amino acid uptake by plants, multiple biases may arise from pre-uptake mineralization by microorganisms or post-uptake metabolism by the plant. We propose the combination of different isotopic analysis methods with molecule isotopologues as a novel approach to improve the accuracy of measured amino acid uptake rates in the total N budget of cucumber seedlings and provide a better characterization of post-uptake metabolism. Cucumber seedlings were exposed to solutions containing L-Ala-1-13C,15N or U-L-Ala-13C3,15N, in combination with ammonium nitrate, at total N concentrations ranging from 0 to 15 mM N and at inorganic/organic N ratios from 10:1 to 500:1. Roots and shoots were then subjected to bulk stable isotope analysis (BSIA) by Isotope Ratio Mass Spectrometry (IRMS), and to compound-specific stable isotope analysis (CSIA) of the free amino acids by Gas Chromatography – Combustion – Isotope Ratio Mass Spectrometry (GC-C-IRMS). Plants exposed to a lower inorganic:organic N ratio acquired up to 6.84% of their N from alanine, compared with 0.94% at higher ratio. No 13C from L-Ala-1-13C,15N was found in shoot tissues suggesting that post-uptake metabolism of Ala leads to the loss of the carboxyl-C as CO2. CSIA of the free amino acids in roots confirmed that intact Ala is indeed taken up by the roots, but that it is rapidly metabolized. C atoms other than from the carboxyl group and amino-N from Ala are assimilated in other amino acids, predominantly Glu, Gln, Asp, and Asn. Uptake rates reported by CSIA of the free amino acids are nevertheless much lower (16–64 times) than those reported by BSIA. Combining the use of isotopologues of amino acids with compound-specific isotope analysis helps reduce the bias in the assessment of organic N uptake and improves the understanding of organic N assimilation especially in the context of organic horticulture

Impact of water quality and irrigation management on organic greenhouse horticulture

Water quality and water supply are essential for organic greenhouse grown crops to prevent soil contaminationby undesirable chemicals and microorganisms, while providing a sufficient amount of water for plant growth.The absence of natural precipitation combined with higher evapotranspiration due to higher temperatureand longer cropping period requires an adequate supply of water. Water quality is commonly defined by itschemical, physical, and biological attributes. It is closely linked to the soil/rock native components, surroundingenvironment and land use. The runoff from urban, industrial, farming, mining, and forestry activities alsosignificantly affects the quality of water available for greenhouse horticulture. High water quality is particularlyimportant in organic greenhouse production in order to prevent soil salinization and ensure optimal soil biologicalactivity. Indeed, unbalanced organic fertilizer inputs may contribute to soil salinity, while soil microbial activitiesresponsible for nutrient mineralization, soil suppressiveness and plant health, are affected by soil pH, ions, andcontaminants. Poor water quality can also result in drip and micro irrigation clogging, plant toxicity, and productcontamination by human pathogen or illicit compounds.To achieve sustainable water management, good knowledge of crops' water requirements is essential as isknowledge of the soil water characteristics that determine the irrigation scheduling. Moreover, the adequacyof the irrigation distribution system determines the accuracy of the water supplied. Crop water needs areoften determined on the basis of daily evapotranspiration and solar radiation levels. Different irrigation controltools such as soil moisture sensors, plant sensors, lysimeters and models contribute to the optimization of theirrigation management of organic greenhouse crops. In addition to determining crop productivity, water qualityand water management also impact on product quality.In this booklet we first illustrate the water flows through different organic greenhouse growing systems. Westate the importance of water quality for organic greenhouse horticulture and give some guidelines regardingthe required water quality attributes in terms of inorganic, organic and microbial loads as well as hazardousmicroorganisms and compounds. We also define advantages and disadvantages of different water resourcesand describe the important drivers for crop and soil water demand. We then report the effects of salinity on soilmineralisation and crop development in organic greenhouse production systems. The main irrigation technologyused for organic greenhouse horticulture is described along with the most important management aspects forirrigation. Because quality attributes of greenhouse products drive consumer demand for organic products, wedefine the impact of water quality and irrigation management on product quality. Organic farming should usecultural practices that maintain land resources and ecological balance, in addition to promoting biodiversity,biological cycles, and soil biological activity. We therefore state the importance of water resources and their usefor organic greenhouse system sustainability. We then conclude by summarizing main aspects of water qualityand irrigation management, and by identifying knowledge gaps.Better prediction of the temporal dynamics of plant and soil microbial water needs in relation to sustainableproductivity and high water use efficiency is needed for greenhouse horticultural crops. It is also importantin terms of reduced attractiveness to pests and susceptibility to diseases. A reduction in spatial and temporalcrop heterogeneity should result from improved growing systems and better water and crop management.Nevertheless, advances in irrigation management for conventional greenhouse crops and development of newcontrol tools can be adapted for use in organic greenhouse horticulture. Similarly, some water treatmentsof drained or collected waters such as thermal, UV, ozone and biological treatments can be used by growersaccording to their organic regulation. Consequently, research is needed in different areas of organic greenhousehorticulture: (i) water quality in terms of relevant thresholds for contaminants and potential risks related toplant and human pathogens; (ii) efficient measures to prevent clogging of the irrigation systems; (iii) alternativewater treatments and system cleaning products; (iv) better knowledge and guidelines for non-leaching systems;(v) affordable and highly efficient control tools to assist growers; and (vi) knowledge about the environmentalimpact of different water management and water sources used for organic greenhouse horticulture to helpgrowers fulfilling the organic principles and improve their sustainability

Biostimulants Promote Plant Development, Crop Productivity, and Fruit Quality of Protected Strawberries

Berries such as strawberries are recognized as a significant constituent of healthy human diets owing to their bioactive secondary metabolites. To improve crop sustainability, yield and berry quality, alternative production systems should be proposed such as organic farming and the use of biostimulants. Thus, we have compared within a complete randomized block design seven biostimulant treatments: 1-control, 2-seaweed extract, 3-Trichoderma, 4-mycorrhiza, 5-mixture of three bacteria, 6-combination of mycorrhiza + bacteria, and 7-citric acid. Strawberry plants were grown in conventional high tunnel (CH), conventional greenhouse (CG) and organic greenhouse (OG). Our results showed that biostimulants did not impact the soil microbial activity (FDA) when compared with the control. Leaf chlorophyll content and photosynthetic leaf performance were not affected by any studied biostimulants. Bacteria, citric acid, and the combination of mycorrhiza + bacteria increased the number of flowering stalks compared with the control in CH, while bacteria increased the crown diameter and all biostimulants increased fresh and dry shoot plant biomass. Citric acid increased leaf Ca content in CG, when all biostimulants increased leaf N content in CH. Studied biostimulants increased berry productivity in CH, while citric acid treatment had the highest yield in CG. The anthocyanins content increased with the use of biostimulants in CH, whereas Trichoderma (CG) and the combination of mycorrhiza + bacteria (OG) increased the Brix, total polyphenols, and anthocyanin contents of the berries compared with the control

Changes in mineral content and CO2 release from organic greenhouse soils incubated under two different temperatures and moisture conditions

In organic greenhouse vegetable productions, the turnover rate of organic amendments may be a limiting factor for optimal crop productivity and quality. Hence, we determined the mineralization potential of several organic greenhouse soils maintained at two temperatures (17, 23C) and water potentials (–35, –250 mbars). Replicate cores of structurally intact soils were collected in plastic cylinders, saturated with water and adjusted to the appropriate matric potential. Additional soil samples were sieved, placed in glass jars and incubated under the same treatment conditions. Soil nutrients, gas concentration (O2, CO2, N2O) and microbial activity (CO2 release) were measured over a 25-week period during aerobic incubation. Large variations in nutrient and organic matter content were observed among intact soil samples. CO2 efflux declined exponentially with time, decreases being most apparent in soils having high organic matter content. An increase in temperature lead to enhanced soil respiration rates, mainly during the first weeks of incubation. Overall, mineralization rates were only slightly affected by moisture level or temperature. Gas diffusion, and thus soil biological activity, may be momentarily hindered during frequent irrigations. Yet, our findings indicate that in general matric potentials of –35 and –250 mbars both result in similar mineralization rates in these soils

Reducing peat in growing media: impact on N content, microbial activity and CO2 and N2O emissions

Renewable materials including coir, biochar and composts are investigated worldwide in the horticultural industry to partially substitute peat in growing media. In this study, we assessed the effects of biochar and vermicompost as partial substitution of peat, and compared these peat-based growing media with coir in terms of NH4+-N and NO3--N content, CO2-C and N2O-N emissions and their microbial biomass carbon (MBC) and nitrogen (MBN). Six growing media mixtures (peat; peat+biochar 9:1 v/v; peat+vermicompost 9:1 v/v; coir; coir+biochar 9:1 v/v; coir+vermicompost 9:1 v/v) replicated three times were incubated in growth chambers during a 60-days period. At day 0 of incubation (DAI), peat amended with biochar retained around 12.81% of NH4+-N compared with peat alone. The concentrations of NO3--N peaked at 275 mg kg–1 at 33 DAI for peat and 552 mg kg–1 at 46 DAI for coir amended with vermicompost. The substitution of peat with biochar resulted in large CO2-C (2070 g CO2-C g–1 dry weight (dw)) and N2O-N (62.78 g N2O-N g–1 dw) emissions, but not coir. The substitution of coir with vermicompost increased N2O-N emissions at a much lower level (47.53 g N2O-N g–1 dw) than peat (111.82 g N2O-N g–1 dw). Our results showed that supplements of vermicompost in peat and coir improved N supply which could benefit plant growth, while substituting part of peat with biochar increased CO2-C and N2O-N emissions. In contrast, no effect of biochar was observed with coir, which is beneficial for the environmental footprint of short-cycle growing crops.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author