Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Land-Management Options for Greenhouse Gas Removal and Their Impacts on Ecosystem Services and the Sustainable Development Goals
    Smith, Pete ; Adams, Justin ; Beerling, David J. ; Beringer, Tim ; Calvin, Katherine V. ; Fuss, Sabine ; Griscom, Bronson ; Hagemann, Nikolas ; Kammann, Claudia ; Kraxner, Florian ; Minx, Jan C. ; Popp, Alexander ; Renforth, Phil ; Vicente Vicente, Jose Luis ; Keesstra, Saskia - \ 2019
    Annual Review of Environment and Resources 44 (2019). - ISSN 1543-5938 - p. 255 - 286.
    afforestation/reforestation - BECCS - biochar - bioenergy with carbon capture and storage - carbon dioxide removal - CDR - ecosystem services - greenhouse gas removal - Nature's Contributions to People - NCPs - negative emission technology - NET - SDG - soil carbon sequestration - terrestrial enhanced weathering - UN Sustainable Development Goals - wetland restoration

    Land-management options for greenhouse gas removal (GGR) include afforestation or reforestation (AR), wetland restoration, soil carbon sequestration (SCS), biochar, terrestrial enhanced weathering (TEW), and bioenergy with carbon capture and storage (BECCS). We assess the opportunities and risks associated with these options through the lens of their potential impacts on ecosystem services (Nature's Contributions to People; NCPs) and the United Nations Sustainable Development Goals (SDGs). We find that all land-based GGR options contribute positively to at least some NCPs and SDGs. Wetland restoration and SCS almost exclusively deliver positive impacts. A few GGR options, such as afforestation, BECCS, and biochar potentially impact negatively some NCPs and SDGs, particularly when implemented at scale, largely through competition for land. For those that present risks or are least understood, more research is required, and demonstration projects need to proceed with caution. For options that present low risks and provide cobenefits, implementation can proceed more rapidly following no-regrets principles.

    Lactic acid fermentation of human excreta for agricultural application
    Andreev, Nadejda - \ 2017
    Wageningen University. Promotor(en): P.N.L. Lens, co-promotor(en): B. Boincean; M. Ronteltap. - Leiden : CRC Press/Balkema - ISBN 9781138049895 - 207
    lactic acid - manure fermentation - fermentation - fertilizers - human faeces - biochar - composting - melkzuur - mestvergisting - fermentatie - kunstmeststoffen - mensenfeces - biochar - compostering

    Human excreta is a valuable fertilizer for improving soil quality and crop productivity, with a potential to replace or complement the mineral fertilizers. The main challenges related to human excreta regarding agricultural applications are microbial contamination risks, loss of nutrients, and odor issues. Fertilization by lacto-fermented faeces supplemented by biochar has benefits such as improved soil bulk density, nitrate and potassium concentrations as well as the yield and yield components of corn, compared to untreated, simple stored faeces, urine, cattle manure, and unfertilized controls. Even though the mineral fertilizer produced corn with significantly higher height and leaf length, it did not add significantly higher yields than lacto-fermented faeces supplemented by biochar. A faeces treatment process by combined lacto-fermentation with thermophilic composting and biochar supplementation had better reduction of coliforms, Escherichia coli, Enterococcus faecalis and Clostridium perfringens, and higher germination of radish and growth of tomatoes than combined lacto-fermentation with vermicomposting. Urine lacto-fermentation contributed to a pH reduction below 4, a decrease in the ammonium concentration and odor strength, as well as an increase in the germination rates compared to untreated stored urine. The results of this study provide important information that can set the basis for scaling up a sustainable technology for the treatment of source separated human excreta while improving its potential for resource recovery.

    Biochar boosts tropical but not temperate crop yields
    Jeffery, Simon ; Abalos Rodriguez, Diego ; Prodana, Marija ; Bastos, Ana Catarina ; Groenigen, Jan Willem van; Hungate, Bruce A. ; Verheijen, Frank - \ 2017
    Environmental Research Letters 12 (2017)5. - ISSN 1748-9318
    biochar - crop yield - meta-analysis - soil

    Applying biochar to soil is thought to have multiple benefits, from helping mitigate climate change [1, 2], to managing waste [3] to conserving soil [4]. Biochar is also widely assumed to boost crop yield [5, 6], but there is controversy regarding the extent and cause of any yield benefit [7]. Here we use a global-scale meta-analysis to show that biochar has, on average, no effect on crop yield in temperate latitudes, yet elicits a 25% average increase in yield in the tropics. In the tropics, biochar increased yield through liming and fertilization, consistent with the low soil pH, low fertility, and low fertilizer inputs typical of arable tropical soils. We also found that, in tropical soils, high-nutrient biochar inputs stimulated yield substantially more than low-nutrient biochar, further supporting the role of nutrient fertilization in the observed yield stimulation. In contrast, arable soils in temperate regions are moderate in pH, higher in fertility, and generally receive higher fertilizer inputs, leaving little room for additional benefits from biochar. Our findings demonstrate that the yield-stimulating effects of biochar are not universal, but may especially benefit agriculture in low-nutrient, acidic soils in the tropics. Biochar management in temperate zones should focus on potential non-yield benefits such as lime and fertilizer cost savings, greenhouse gas emissions control, and other ecosystem services.

    Verrassende materialen zetten onderzoekers op duurzaam spoor
    Blok, Chris - \ 2016
    substrates - polylactic acid - biochar - greenhouse horticulture - innovations - biobased materials - biobased economy - substitutes
    Bodemverbeteraars met focus op biochar
    Reuler, H. van; Baltissen, A.H.M.C. - \ 2016
    - 15
    bodemverbeteraars - biochar - bodemkwaliteit - bodemvruchtbaarheid - bodembiologie - soil conditioners - biochar - soil quality - soil fertility - soil biology
    Biochar is een stabiele organische verbinding die hoofdzakelijk uit koolstof bestaat. Het ontstaat bij verhitting van biomassa onder zuurstofloze omstandigheden, z.g. pyrolyse. Biochar wordt geproduceerd als bodemverbeteraar. De discussie gaat om het effect van Biochar toediening op een aantal bodemfuncties, zoals b.v. het vermogen om vocht en voedingsstoffen vast te houden, biologische activiteit.
    Biomassa voor de energievoorziening van tuinbouwclusters
    Zwart, H.F. de; Ruijs, M.N.A. ; Visser, H.J.M. - \ 2016
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1393) - 34
    bio-energie - glastuinbouw - haalbaarheidsstudies - economische haalbaarheid - warmte - kooldioxide - elektriciteit - biomassa - biobased economy - biochar - verbranding - opwekking van elektriciteit - warmteproductie - bioenergy - greenhouse horticulture - feasibility studies - economic viability - heat - carbon dioxide - electricity - biomass - biobased economy - biochar - combustion - electricity generation - heat production
    Biomass combustion in combination with a cluster of greenhouses to provide heat, CO2 and electricity can provide a partly solution to the sustainability of the horticultural sector. A biomass gasification plant could also provide valuable biochar, the result of partial combustion of biocarbon. This was shown to have attractive characteristics to be used in high quality potting soil. Despite the high value of the biochar (contributing for 16% of the income from the plant), the economic feasibility of a biomass combustion plant depends heavily on governmental subsidies (SDE +). When the developed technology is used on a practical scale, a biomass plant of 8 MW thermal power and 1.4 MW of electrical power is a sound size. Such a plant fits well with a horticultural cluster of 15 hectares, consisting of 6 ha Tomato, 6 ha Pepper and 3 hectares of Chrysanthemum. The biomass plant produces over 91% of the heating and 95% of the CO2 requirement and 67% of the electricity counsumed. However during winter a lot of electricity will have to be bought, which is compensated with selling to the public grid in summer. The biomass combustion plant will mainly run on biomass is supplied from elsewhere. The biomass from the local cluster covers only 0.3% of the combusted amount. If all available biomass from Netherlands territory would be used to heat greenhouses about 20% of greenhouse industry could make use of system like described in this report.
    Onderzoek biochar als potgrond en drager voor levende biostimulanten : geschikt als gedeeltelijke vervanger van veen
    Blok, Chris - \ 2016
    horticulture - greenhouse horticulture - pot plants - chrysanthemum - gerbera - growing media - biochar - trials - soil conditioners

    Bij nieuwe productiemethoden van biogas en -olie blijft als restproduct biochar over. Dat is geschikt als toevoeging in potgronden, blijkt uit lab- en kasproeven. Ook kan dit restproduct wellicht dienen als drager voor nuttige bodemorganismen, die daardoor beter aanslaan.

    Recovery of nutrients from biogas digestate with biochar and clinoptilolite
    Kocaturk, N.P. - \ 2016
    Wageningen University. Promotor(en): L. Stoumann Jensen; Lijbert Brussaard, co-promotor(en): S. Bruun; Kor Zwart. - Wageningen : Wageningen University - ISBN 9789462578234 - 130
    biochar - clinoptilolite - digestate - nutrients - waste management - fractionation - growth - biochar - clinoptiloliet - digestaat - voedingsstoffen - afvalbeheer - fractionering - groei

    The liquid fraction of digestate contains nutrients which makes it a valuable fertiliser in agricultural crop production systems. However, direct application of digestate may raise practical and environmental problems. Therefore, processes to concentrate nutrients have been proposed aiming not only to treat the liquid fraction of digestate to overcome the problems related to direct application, but also to recover the nutrients of which natural reserves are being depleted such as phosphorus and potassium.

    In this thesis, the focus was on the evaluation of the use of clinoptilolite and biochar for nutrient recovery from the liquid fraction of digestate; and to investigate the further use of these nutrient-enriched materials as fertiliser.

    This thesis showed that sorption with clinoptilolite and biochar can be a promising technology to recover nutrients from liquid fraction of digestate. Using biochar and clinoptilolite provides concentration of nutrients and, thereby, volume reduction which allows for savings on storage, transport and application of the voluminous liquid fraction of digestate. The end-products are digestate-enriched clinoptilolite and enriched biochar can act as N fertilisers.

    Coco peat and biochar are good alternatives for peat in potting soil : researchers and producers search for new raw materials
    Blok, Chris - \ 2016
    growing media - peat - substitutes - coconut products - coir - biochar - greenhouse horticulture - biobased materials
    Effecten bodem- en structuurverbeteraars : Onderzoek op klei- en zandgrond 2010-2015 eindrapportage
    Balen, D.J.M. van; Topper, C.G. ; Geel, W.C.A. van; Berg, W. van den; Haas, M.J.G. de; Bussink, Wim ; Schoutsen, M.A. - \ 2016
    Lelystad : Praktijkonderzoek Plant & Omgeving, onderdeel van Wageningen UR, Business Unit Akkerbouw, Groene Ruimte en Vollegrondsgroenten - 121
    bodemkwaliteit - bodemstructuur - fysische bodemeigenschappen - chemische bodemeigenschappen - bodembiologie - bodemvruchtbaarheid - bodemvruchtbaarheidsbeheer - zware kleigronden - zandgronden - calciummeststoffen - biochar - soil quality - soil structure - soil physical properties - soil chemical properties - soil biology - soil fertility - soil fertility management - clay soils - sandy soils - calcium fertilizers - biochar
    In de praktijk lopen telers vaak tegen problemen aan van een slechte bodemkwaliteit. Intensieve bouwplannen, steeds zwaardere mechanisatie, uitloging (Ca-uitspoeling), piekneerslagen en de schaalvergroting in de landbouw leiden tot vermindering van de fysische bodemvruchtbaarheid en de structuur van de bodem. Dit veroorzaakt:  toenemende problemen bij de bewerkbaarheid van de bodem;  minder efficiënt gebruik van meststoffen;  verhoogd risico van uit- en afspoeling van nutriënten;  wateroverlast;  verlaging van de opbrengst. Om de bodemstructuur te verbeteren, worden door industrie en handel zogeheten bodemverbeteraars en kalkmeststoffen aangeboden. Er is een grote variatie in type producten, de wijze waarop ze werken en de mate waarin ze een directe dan wel indirecte invloed op de bodemvruchtbaarheid kunnen hebben. Objectieve informatie over het effect van deze producten op de gewasopbrengsten en de fysische, chemische en biologische bodemvruchtbaarheid ontbreekt. Uit eerdere proeven is bekend dat effecten van bodem verbeterende maatregelen vaak pas na enkele jaren zichtbaar worden. Om het effect van verschillende bodemverbeteraars op opbrengst en bodemeigenschappen op de langere termijn te toetsen, zijn proefvelden aangelegd op drie kleilocaties (Kollumerwaard, Lelystad en Westmaas) en twee zandlocaties (Vredepeel, Valthermond). Op deze proefvelden zijn bouwplannen toegepast die gangbaar zijn voor de betreffende regio. Eventuele positieve effecten worden sterker met het verstrijken der jaren. Bovendien zijn deze het duidelijkst te onderscheiden wanneer op alle locaties hetzelfde gewas wordt geteeld. Daarom stonden er in het laatste jaar op alle proefvelden aardappels. In de proef zijn de ontwikkeling van de gewasopbrengst, de gewaskwaliteit en de bodemeigenschappen gevolgd over een periode van zes jaar (2010-2015).
    Perspectives for the use of biochar in horticulture
    Blok, C. ; Regelink, I.C. ; Hofland-Zijlstra, J.D. ; Streminska, M.A. ; Eveleens-Clark, B.A. ; Bolhuis, P.R. - \ 2016
    Bleiswijk : Wageningen UR Glastuinbouw (Rapport GTB 1388) - 42
    biochar - growing media - greenhouse horticulture - pot experimentation - soil chemistry - soil properties - residual streams - biobased economy - biochar - groeimedia - glastuinbouw - potproeven - bodemchemie - bodemeigenschappen - reststromen - biobased economy
    Biochars were produced using different production parameters and consequently measured in a rooting media laboratory and used as a constituent in potting soil mixes for 8 and 12 week growth experiments. The biochar feedstock influences the biochar’s eventual nutrient and salt content, the pH, the buffer capacity and the cation exchange capacity all of which can potentially hamper normal growth. It is indicated which materials may result in effective biochars regarding nutrient and salt content. A method to measure and compensate unwanted pHs is described and validated. The production parameters are shown to influence growth defining properties such as phytotoxicity, water behaviour and degradability. Finally growth experiments with mixes of biochar and other rooting media constituents were performed and used for further advice on compensating unwanted properties. In the experiments up to 20%-v/v biochar was used without adverse effects on production. De lab results indicate the maximum amounts could at least be 25%-v/v when mixing with rooting media constituents with sufficiently complementary properties. Porous biochars are shown to be able to host microbial life but to fully utilize this promising trait more rigorous pretreatment of the biochar particles are suggested.
    Pathogen removal using saturated sand colums supplemented with hydrochar
    Chung, J.W. - \ 2015
    Wageningen University. Promotor(en): Piet Lens, co-promotor(en): J.W. Foppen. - Leiden : CRC Press/Balkema - ISBN 9789462574977 - 156
    drinkwater - afvalwaterbehandeling - biochar - biomassaconversie - pyrolyse - micro-organismen - gezondheidsgevaren - volksgezondheid - drinking water - waste water treatment - biochar - biomass conversion - pyrolysis - microorganisms - health hazards - public health

    This PhD study has evaluated hydrochars derived from biowastes as adsorbents for pathogen removal in water treatment. Pathogen removal experiments were conducted by carrying out breakthrough analysis using a simple sand filtration set-up. Glass columns packed by 10 cm sand bed supplemented with minor amount of hydrochar (1.5 %, w/w) were flushed with artificial ground water seeded with test microorganisms at an upward flow rate of 1 mL / min. Either back flushing or deionized water flushing was performed at pathogen retaining columns in order to investigate the pathogen removal mechanism of hydrochar-amended sand columns.

    Two home-made two-step reverse transcription-quantitative polymerase chain reaction assays were developed in order to quantify rotavirus in the samples from virus removal experiments. Since the total cost of the assays was mainly determined by the cost of reverse transcriptase, two reverse transcriptases with the lowest consumer price were employed. The efficiencies of home-made assays were comparable to a selected reference commercial kit in analyzing both environmental and laboratory samples, while the total cost of home-made assays was 11 times less. Though home-made assays necessitate more manual operations and time, the low-cost aspect might be appealing in those settings where the expenditure for consumables inhibits laboratories in their functioning.

    Hydrochars produced via hydrothermal carbonization of agricultural residue from maize or stabilized sewage sludge were evaluated for adsorptive removal of Escherichia coli. In order to improve the removal capacity, the hydrochars were activated by being suspended in 1M KOH solution (5 g hydrochar / L) for 1 h at room temperature. The activation improved the Escherichia coli removal efficiency from ~70 to ~90 %. In addition, successive detachment experiments carried out by performing back flushing or deionized water flushing into sand columns supplemented with maize-derived hydrochar indicated that the strength of Escherichia coli attachment increased by KOH activation. Also, Escherichia coli removal of sewage sludge-derived hydrochar was evaluated in larger column with 50 cm filter bed for 30 days of intermittent operation. 3 pairs of columns packed with either sand, raw hydrochar or activated hydrochar showed average removal efficiency of 36.5% ± 10.1 (n=60), 24.4% ± 10.5 (n=56) and 91.2% ± 7.5 (n=60), respectively. Idle time of filtration unit did not affect the Escherichia coli removal efficiency of hydrochar-amended columns. The results from material characterization attributed the enhancement in Escherichia coli removal induced from the KOH activation to development of macroporous surface with increased hydrophobicity and surface charge. It was apparent that the activation with the KOH solution removed tar-like substances from hydrochar surface, resulting in exposure of hydrophobic core and development of rough surface structure. Also, deposition of K+ ion in hydrochar was observed, which might have increased the surface charge.

    The removal of human pathogenic rotavirus and adenovirus was investigated using hydrochar derived from stabilized sewage sludge or swine faecal waste. Throughout virus removal experiments, rotavirus and adenovirus showed comparable removal. At 1 mL / min flow rate, raw hydrochar (without KOH activation) derived from either feedstock showed mean virus removal efficiency from 2 to 3 > log removal (99 - 100 %). Also flow rates of 2.5 and 5 mL / min were tested using faecal waste-derived hydrochar. The virus removal efficiency remained still high (2.1 log - 3 log) at the elevated flow rates. We speculated that the improvement in virus removal derived from hydrochar supplement is induced by provision of extra hydrophobic surfaces in sand column media. Regardless the type of packing material, successive deionized water flushing into virus-retaining columns released more rotavirus than adenovirus, indicating larger role of the secondary energy minimum in rotavirus retention. It was remarkable, because both types of viruses are similar in their shape and size. This observation provides evidence that virus transport-retention behaviour could be mainly determined by surface characteristics of virus rather than its size and shape. In this sense, the use of model virus needs to be carefully considered when performing water treatment or pathogen transport experiments.

    Successful removal of pathogenic virus using faecal waste-derived hydrochar highlights the potential of hydrothermal carbonization technology in less developed regions where modern water-sanitation systems are not affordable. Faecal waste, one of the most important pathogen sources, can be completely sanitized in elevated temperature and pressure during hydrothermal carbonization process. Moreover, the resulting hydrochar can be utilized at water or wastewater treatment. Despite general low-cost aspect of hydrothermal carbonization such as less energy dependency than dry pyrolysis and utilization of waste as a feedstock, the need for high-pressure reactor might hamper the implementation of the technology. Development of localized low-cost reactor, evaluation of hydrochar in its use at agriculture and/or energy production and overall economic analysis are recommended.


    Disease suppression in cropping systems
    Postma, Joeke - \ 2015
    strawberries - small fruits - plant protection - fungus control - phytophthora cactorum - suppression - mycorrhizas - composts - biological control - biochar
    Phosphorus mobilization and biocontrol of plant pathogens combined in one strain – results of a fungus and a bacterial inoculant
    Postma, J. ; Nijhuis, E.H. - \ 2015
    aardbeien - tomaten - potproeven - gewasbescherming - grondverbeteraars - compost - biochar - schimmelbestrijding - biologische bestrijding - glastuinbouw - mycorrhizae - fosfor - strawberries - tomatoes - pot experimentation - plant protection - soil amendments - composts - biochar - fungus control - biological control - greenhouse horticulture - mycorrhizas - phosphorus
    How two important crops, strawberry and tomato grown in potting soil, benefit from microbial inoculants.
    Kokos en biochar geschikte alternatieven voor veen in potgrond : zoektoch potplantensector naar nieuwe grondstoffen
    Rodenburg, J. ; Blok, C. - \ 2015
    Onder Glas 12 (2015)8. - p. 7 - 9.
    potplanten - groeimedia - biochar - bodemverbeteraars - houtskool - koolstofvastlegging in de bodem - kokos - samenstelling - sierplanten - gebruikswaarde - glastuinbouw - pot plants - growing media - biochar - soil conditioners - charcoal - soil carbon sequestration - copra - composition - ornamental plants - use value - greenhouse horticulture
    De meeste potgronden bestaan voor een groot deel uit veen. Maar er is een duidelijke kentering merkbaar. Telers, afnemers en consumenten vragen steeds vaker om veenvrije mengsels. Redenen zijn de grote hoeveelheid CO2 die vrijkomt bij afgravingen en het verloren gaan van eeuwenoude moerasgronden. Onder meer daarom startte een zoektocht naar nieuwe grondstoffen voor potgrond. Met kokos is al veel ervaring opgedaan en biochar heeft de potentie om een belangrijk ingrediënt met meerwaarde te worden.
    Challenging the claims on the potential of biochar to mitigate climate change
    Francischinelli Rittl, T. - \ 2015
    Wageningen University. Promotor(en): Thomas Kuijper; Ellis Hoffland; Bas Arts, co-promotor(en): E.H. Novotny. - Wageningen : Wageningen University - ISBN 9789462573253 - 145
    klimaatverandering - mitigatie - biochar - bodem - organische koolstof - vloeistofchromatografie - koolstofvastlegging in de bodem - brazilië - climatic change - mitigation - biochar - soil - organic carbon - liquid chromatography - soil carbon sequestration - brazil


    In this PhD thesis I studied the influence of biochar discourses on the political practices in Brazil and the impact of biochar on soil organic carbon (SOC) stocks, thus contributing to the current debate on the potential of biochar to mitigate climate change. Biochar is the solid material obtained from the carbonization of biomass. The deliberate production and application to soil distinguishes biochar from other carbonized products, e.g. charcoal. Inspired by the aged charcoal found in the fertile Amazonian Dark Earth (ADE; also known as Terra Preta de Índio), the current application of biochar in soil is claimed to simultaneously address four global challenges: food production, climate change, energy supply and waste reduction (Chapter 1). Biochar is supposed to be an absorbent and stable material, which can be used to retain nutrients in the soil, increasing agricultural productivity, while sequestering carbon over extended periods of time. Therefore, biochar is claimed to be a means to mitigate global climate change. Furthermore, if biochar is produced in a modern pyrolysis plant, it also can co-produce bio-oil and syngas that could be used as energy. And if biochar is produced by carbonization of agricultural residue, biochar may reduce the quantity of solid waste that needs to be disposed of.

    In Chapter 2, I analysed the policy arrangement related to biochar along the four dimensions of the policy arrangement approach, which are actors, discourse, power and rules. I focused on Brazil, which is an important player in the international biochar debate. My analysis shows that scientists in research institutions are the dominant players in the network, while policymakers, businessmen and farmers are marginally positioned. Experts from Embrapa occupy central positions and thus exercise most power in the network. Moreover, experts linked to ADE have lost prominence in the network. The cause for this reduction was the shift from the ADE/biochar to the biochar/technology discourse. The latter discourse includes different coalitions, such as: ‘climate change mitigation’, ‘improvement of soil fertility’ and ‘improving crop residue management’. Although the biochar/climate coalition is dominant at international level, it is far less prominent in Brazil. Nationally the discourses of ‘improvement of soil fertility’ and ‘improving crop residue management’ have particularly prompted actors’ relationships and practices. However, the biochar/technology discourse is not (yet) institutionalized into formal rules in Brazil.

    As a consequence, the country lacks an established biochar policy field. Brazilian biochar practices focus on the carbonization of the available residues into biochar and on the application of biochar in soils to increase the SOC content and consequently the fertility of these soils. In this context, in Chapter 3 I tested in the field the potential of biochar produced in traditional kilns to increase the C contents of sandy savannah soils. My results show that biochar produced in traditional kilns is less thermally altered than that produced by industrial kilns and therefore rapidly decomposes. The decomposition rate of traditionally produced biochar was higher (decomposition constant k = 0.32-1.00 year-1) than generally assumed (k = 0.0005-0.005 year-1), and higher than the decomposition of native SOC (k = 0.22 year-1). In Chapter 4 I demonstrated in a short-term laboratory experiment that oilseed-derived biochar had a similar or higher decomposition rate than native SOC. My results show that all three tested oilseed biochars decelerate the decomposition of SOC in the biochar-amended soils, with biochar richer in aromatics having a stronger negative effect than biochar richer in aliphatics. Therefore, oilseed biochar directly increases soil C stocks and indirectly raises soil C sequestration in the short term through decreasing the decomposition of native SOC.

    In my research, the decomposition studies were performed using 13C isotope analysis. However, the 13C isotope analysis cannot be used when the differences of 13C isotope abundance between biochar and soil are not sufficiently large. Therefore, its use can be limited. In Chapter 5, I aimed at improving the benzene polycarboxylic acid (BPCA) method. I re-designed the protocols of the BPCA method and found a better and faster way to quantify and characterize the BPCAs derived from biochar, compared to the previous protocols. The improved method was then successfully tested and implemented in a laboratory in Brazil.

    Combining my findings with results of the literature, I conclude (Chapter 6) that there is no evidence that biochar is a reliable way for C sequestration in sandy soils under savannah environments. Biochar decomposition is highly variable, depending on charring conditions, soil and climate: (i) biochar produced by traditional kilns is less thermally degraded than those pyrolysed by industrial kilns; (ii) in sandy soils less biochar accumulates than in clay-silt soils; and (iii) warm-dry conditions raise the decomposition of biochar. These conclusions have a direct consequence for the development of policies on biochar, because we cannot ensure that biochar will sequester the same quantity of C for the same period at different geographical regions.

    The ancient secrets of black soil
    Voorde, T.F.J. van de - \ 2014
    soil - biomass - carbon - biochar
    Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns
    Sagrilo, E. - \ 2014
    Wageningen University. Promotor(en): Thomas Kuijper; Ellis Hoffland. - Wageningen : Wageningen University - ISBN 9789462571679 - 128
    organisch bodemmateriaal - grondverbeteraars - koolstofvastlegging in de bodem - vesiculair-arbusculaire mycorrhizae - bodemvruchtbaarheid - glycine max - biochar - stikstoffixatie - kooldioxide - emissie - brazilië - soil organic matter - soil amendments - soil carbon sequestration - vesicular arbuscular mycorrhizas - soil fertility - glycine max - biochar - nitrogen fixation - carbon dioxide - emission - brazil

    Soil and plant responses to pyrogenic organic matter: carbon stability and symbiotic patterns

    Edvaldo Sagrilo


    Pyrogenic organic matter (PyOM), also known as biochar, is the product of biomass combustion under low oxygen concentration. There is currently a growing interest in research on the use of PyOM as a soil amendment, inspired by the existence of highly fertile, PyOM-rich anthropogenic soils in the Amazon basin. The presence of PyOM in these so-called Amazonian Dark Earths (ADE) in quantities larger than in the non-anthropogenic surrounding soils is considered one of the main reasons for their high fertility.

    Soil additions of PyOM have been suggested to increase soil fertility and crop yields, simultaneously providing additional important environmental services. The offset of CO2 emissions through sequestration of a larger pool of recalcitrant soil organic carbon (SOC) is one of these services. This would at the same time sustain soil microbial activity, which is directly associated to soil quality, for instance, nutrient cycles and plant growth. This multiple win scenario suggests that the addition of PyOM to the soil would be the solution for the “carbon dilemma”. The dilemma states that the main biological benefits from soil organic matter are a consequence of its decay. Therefore, it is unlikely that increased C sequestration and the benefits from its decay can be simultaneously maximized. Rather than win-win, PyOM would then also be subjected to inevitable trade-offs.

    Additions of PyOM can modify the turnover rate of native SOC by either accelerating or decelerating its decomposition through a mechanism known as priming. Although positive priming by PyOM has been reported, negative priming has also been found. The higher amount of non-pyrogenic C in ADE, compared to non-anthropogenic surrounding soils has been considered evidence that PyOM can stabilize SOC in the long-term. A complicating issue in studies is that short-term increases in CO2 emission can be due to decomposition of labile PyOM fractions, erroneously suggesting positive priming of SOC. Addition of PyOM can also lead to modifications in the microbial activity and assemblages. Changes in microbial populations can have impacts on their functionality, favouring mutualistic root symbioses such as the arbuscular mycorrhizal fungal (AMF) symbiosis and the rhizobial symbiosis with legumes that is responsible for biological nitrogen fixation (BNF). Although soil amendments with PyOM can stimulate AMF and BNF, results are contrasting and mechanisms are not clear. Most studies of PyOM effects on SOC and on mutualistic root symbioses are from short-term experiments, often conducted in greenhouse or laboratory. Although such studies provide insights in potential factors driving changes in SOC and symbiotic relationships in PyOM-amended soils, they do not assess changes under realistic conditions over periods of time longer that one or a few cropping cycles. Therefore, there is still a gap in our understanding regarding the duration and magnitude of effects over time under field conditions and possible mechanisms involved. This thesis addresses these gaps.

    The aim of this research was to provide a better understanding of interactions between PyOM and SOC and the factors controlling symbiotic patterns in a tropical soil amended with PyOM. To reach this aim, I combined greenhouse and field studies. I also used meta-analytic methods in order to quantitatively synthesize data in literature.

    In Chapter 2, I combined the results of 46 studies in a meta-analysis. I investigated changes in CO2 emission patterns from an array of PyOM-amended soils and identified the causes of these changes and the possible factors involved. I showed an overall increase of 29% in CO2 emission from PyOM-amended soils. Such increases were only evident in soils amended with a PyOM-C (PyC):SOC ratio >2. These data are consistent with the hypothesis that increased CO2 emission after PyOM addition is additive and mainly derived from PyOM’s labile C fractions rather than from SOC. Therefore, positive priming is not a main driver of increases in CO2 emission in PyOM-amended soils. This PyC:SOC ratio provided the best predictor of increases in CO2 production after PyOM addition to soil. This meta-analysis indicates (i) the importance of taking into account the amount of applied PyC in relation to SOC for designing future decomposition experiments and that (ii) the recalcitrance of PyOM in soil-PyOM mixtures may be less than usually assumed.

    A technical problem of separating PyOM-induced priming on SOC from other non-additive interactions is the uncertainty regarding the origin of the respired CO2 (whether from SOC or PyOM). This issue can only be solved with the use of isotopes. In a field study (Chapter 3), I quantified changes in the PyOM and SOC stocks over four soybean cropping cycles (CC) in a sandy Ferralsol, previously supporting a vegetation with C4 plants, amended with different rates of PyOM (0, 5, 10, 20 and 40 Mg ha-1). The PyOM was produced from C3 woody species using traditional pyrolysis methods employed in Northeast Brazil. I used 13C isotopic analysis to discriminate the origin of the C in the soil and quantify the decomposition rates of native SOC and PyOM. I showed that decomposition of traditionally produced PyOM is faster (25-60% within first year) than normally assumed (10-20% within 5-10 years), which was higher than that of native SOC (5-14%). The data indicate preferential decomposition of PyOM compared to native SOC. The intensity of that effect depends on the rate of PyOM applied to the soil. Only on the longer term (>1 yr) addition of PyOM seems to stabilize SOC.

    In Chapter 4 I explored mechanisms controlling AMF activity and crop yield in PyOM-amended soils through the use of path analysis. I tested the effects of PyOM rates and P fertilization on soybean root colonization by AMF, soil P and plant performance over four cropping cycles (CCs). Data showed a major effect of CC and P, as well an interaction effect of PyOM x CC on mycorrhizal colonization. There was a linear decrease in root colonization by AMF in CC1 with increasing PyOM rates in contrast to a consistent linear increase in CC4. Plant performance was mainly affected by CC, but a significant interactive effect of PyOM x P was also observed on grain yield. Grain yield was highest at high PyOM rates (20 and 40 Mg ha-1) in the P-fertilized treatments in CC4. Soil pH increased in CC1 with increasing PyOM rates, but no effects were observed in CC4. Path analysis indicated that PyOM effects on root colonization by AMF were not mediated by changes in soil pH or P content. My data are consistent with the hypothesis that interference of PyOM in signalling processes is an important driver of change in AMF activity and that positive effects of PyOM on AMF and crop yield develop with time.

    In Chapter 5, I assessed the effects of PyOM application rates and P fertilization on BNF in soybean inoculated with Bradyrhizobium japonicum over four cropping cycles. Again I observed that CC had a significant main effect on most dependent variables, while PyOM was not a significant source of variation. There was a significant PyOM × CC interaction effect on shoot N concentration. In CC1 shoot N concentration after application of 5 Mg PyOM was significantly lower than that of plants grown on plots to which 10 or 20 Mg PyOM was applied. In CC4 shoot N concentration was not affected by PyOM. The major effect of CC was explained through changes in nutrient management, more specifically the addition of micronutrients in CC3 and CC4. Alleviation of micronutrient deficiency increased BNF and also resulted in a positive effect of P on BNF. I conclude that under conditions of adequate management, PyOM application does not improve BNF in soybean.

    In Chapter 6 (General Discussion) I synthesize the findings of the previous chapters and use data from additional greenhouse and litterbag field experiments to integrate the results. Data from Chapters 2 and 3 show that if any positive priming occurs due to PyOM addition, it is a small short-term event and does not lead to significant losses of native SOC in the long-term. This was confirmed by data from a 2 yr litterbag experiment, which showed no interaction between decomposition of PyOM and fresh organic matter.

    Stability of SOC has been considered an ecosystem property rather than a consequence of recalcitrance, but this definition has not yet been extended to PyOM. In this thesis I demonstrated that stability of PyOM can also be influenced by the soil environment. In order to link PyOM effects to SOC and on root symbioses, I performed path analysis integrating root colonization by AMF, SOC content and Ndfa in one model. We found no significant path coefficients linking AMF and BNF. The model indicated a significant positive path coefficient linking AMF root colonization and SOC in CC4, but not in CC1. The data suggest that PyOM may increase SOC stability through increased AMF activity. Soil aggregation and C sequestration are tightly correlated with abundance of AMF in the soil. I propose that the same mechanism through which AMF stabilizes native SOC may also positively influence PyOM stabilization in the long-term.

    In conclusion, I have shown that main beneficial effects of PyOM on AMF and crop yield develop with time, but in well-managed soils increased crop yield is not a direct consequence of increased AMF due to PyOM addition. Finally, although PyOM additions represent an effective form of sequestering C, positive effects of PyOM on crop yield are likely to occur after partial decomposition of PyOM. Therefore, although some benefits of adding PyOM can be simultaneously obtained (C sequestration and increased crop yield), they cannot be simultaneously maximized. This means that the carbon dilemma can only be partially solved by adding PyOM to the soil.

    Modification of Biochar to improve its functionality
    Zwart, Kor - \ 2014
    agriculture - soil amendments - soil fertility - biochar - charcoal - soil conditioners - pyrolysis - soil carbon sequestration - quality - modification - chemical processes
    Indianenverhalen over zwarte grond : zoektocht naar de werking van biochar
    Nijland, R. ; Voorde, T.F.J. van de - \ 2014
    WageningenWorld 2014 (2014)1. - ISSN 2210-7908 - p. 34 - 39.
    biochar - bodemvruchtbaarheid - bodemverbeteraars - koolstofvastlegging in de bodem - duurzaamheid (sustainability) - black soils - bodemkunde - biobased economy - biochar - soil fertility - soil conditioners - soil carbon sequestration - sustainability - black soils - soil science - biobased economy
    Een eeuwenoude, door de indianen gebruikte methode voor het verbeteren van de bodem met houtskool, staat weer volop in de belangstelling. De zwarte grond zou het klimaatprobleem oplossen en het regenwoud redden. Maar zo eenvoudig is het niet, blijkt uit onderzoek.
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