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Valorization of landscape residues: The potential of heathland and forest management residues for the ornamental sector in Flanders, Belgium

Book - Dissertation

CH 1 - Since the industrial revolution, artificial fertilizers were essential in our farming systems. However, paradoxically, different regions in Northwestern Europe cope with nutrient surpluses. Flanders, in Belgium, is one of these regions. Actual world challenges accelerate the need for a transition towards a more sustainable bioeconomy. One aspect is the valorization of waste streams. While amounts of biomass are produced by different sectors, other sectors are searching for alternatives for non-renewable resources. This thesis focuses on the potential valorization of residues from heathland and forest management for horticultural uses. In this introductory chapter, the valorization of residual biomass streams is explored, followed by the focus on nature management residues with their potential and uncertainties.PART I - Residue characterization CH 2 - Heathlands are among the most important semi-natural cultural landscapes in Northwestern Europe. High-intensity management techniques, such as plaggen and chopper, are necessary to restore and maintain their unique flora and fauna, but generate substantial amounts of residues that have no sustainable reuse so far. This chapter therefore aims at characterizing these residues and at evaluating their potential as growing medium constituent or soil amendment. Residues are primarily characterized based on their origin and on the management technique used to extract them. We evaluated the spatial distribution of the different residue types and assessed if the used typology also reflects the physicochemical characteristics of the extracted product. Finally, the characteristics of the residues were compared with industrial standards and legal limits for growing media or soil amendments and to other growing media constituents. Our results show a difference between extraction techniques, where sods (plaggen) from forests and heathlands have higher bulk densities, lower organic matter contents, lower lignocellulosic components and lower biodegradation potential, compared to heathland chopper. Analyses further confirm the potential of the residues as a raw material for growing media or soil amendments. Measured pH-H2O and Electrical conductivity (1:5 soil:water (v/v ratio) of the residues fall within acceptable ranges and nutrient contents are low, with beneficial effects on carbon:nitrogen (C:N) and carbon:phosporous (C:P) ratios. Field and pot experiments are needed to evaluate effects on plant growth. CH 3 - In this chapter, we evaluate if rapid, non-destructive screening methods can be applied to quickly assess the properties of biomass waste streams and therefore their potential as a peat-alternative or soil amendment. More specifically, spectroscopy measurement in the visible (VIS) and near infrared (NIR) wavebands was investigated for composts and different types of plant fibres, among which the management residues described in Chapter 2. For that purpose, three datasets are used for calibration and different parameters are integrated in the models: pH-H2O, EC, biochemical compounds such as cellulose, hemicellulose and lignin, biodegradation potential, total nutrient concentrations and the Oxygen Uptake Ratio (OUR). A 10-fold venetian blind cross-validation was performed for all parameters, including preprocessing and variable selection to obtain the most robust models. The models were then validated with an independent set of samples, including plant fibres, composts and peat-based substrates. Based on the coefficient of determination (R²), the root mean square error of cross-validation and of prediction (RMSECV and RMSEP), and the ratio of RMSECV on standard deviation, predictions were evaluated. Differences in prediction were found when using the whole validation set, compared to a subset of the validation set. In general, successful to moderately useful calibrations were obtained for parameters related to organic matter content, while calibrations were less successful for nutrients. Prediction results were not good for the compost sub sets.Part II - Residue valorisationCH 4 - Three residue types (heath chopper, heath plaggen en forest plaggen) were selected to account for variability in vegetation type and management technique, characterized chemically and physically and compared to a reference peat-based growing medium. A pot experiment was conducted in 2016 to evaluate plant growth in different peat:residue growing media (70:30, 40:60, 0:100 % v/v). All growing media complied with the Belgian Federal Legislation (pH-range from 4.5 to 7 and EC < 750 µS cm-1). Juniperus scopulorum 'Blue Arrow', Cornus alba 'Sibirica', Hydrangea paniculata 'Pinky Winky' and Elaeagnus ebbingei were chosen as model plants. Growing media characteristics and plant performance (plant growth and root development) were monitored for four months during the experiment. In general, analysis revealed that the 70:30 and 40:60 % v/v growing media provided favorable growing conditions for all residue types, showing their potential as peat alternative and as novel and local available growing medium constituents in Belgium. In particular forest plaggen and heathland chopper are potential peat alternatives, with heathland chopper showing the best results. Heather plaggen were less performant for plant growth as well as root growth but still provided acceptable results as a peat alternative.In a field trial, the management residues were also amended as soil improver, for nursery plants such as Fagus sylvatica, Alnus glutinosa and Quercus robur. The potential as soil improver was found to be similar to the used green compost, but no significant differences in soil carbon levels were measured.CH 5 - Growing media based on peat are considered non-sustainable, due to high CO2 emissions and destruction of valuable wetland habitat during their production. Therefore, the objective of this chapter was to evaluate the potential of substitution of peat as a growing media constituent by residues generated during nature management for highbush blueberry (Vaccinium corymbosum L. ('Bluecrop')) production. Growth and photosynthetic characteristics of the blueberries were compared during the first months of growth in a typical peat-based container growing medium for Vaccinium spp. versus growth in containers where 30% v/v of peat was replaced by wood chips, forest plaggen or heathland clippings in the growing medium. No significant differences were observed between the high-peat and the reduced-peat treatments. Hence, for horticultural production of blueberries, such residues can be considered a viable, sustainable and readily available peat substitute for growing media. Additionally, the berry-growing sector is searching for alternative soil acidifying agents to cope with irrigation-induced chlorosis. Two experiments were performed to test the potential of residues from nature management for that purpose. For Vaccinium, the three residues mentioned above were tested as mulch or deep mixing and compared to the control soil. Only forest plaggen had a significant pH decreasing effect. For Rubus, a single residue type (i.e. forest plaggen) was used to follow-up effects of mulching and deep mixing and compare it to a control soil with and without amendment of elemental sulphur. Significant differences were found for the treatments with mulch. In general, we concluded that forest plaggen have the potential to be used as an acidifying agent, although a combination with elemental sulphur might be necessary to reach optimal pH valueCH 6- Formulates a final discussion and conclusion to this research, with implications for the different actors in the value chain and with scope for further research, based on what we have learned. Research objectives defined in Chapter 1 are reconsidered
Publication year:2021