Steven Sleutel

• PhD
• Professor (Associate) at Ghent University

With climate change expected to intensify the occurrence and severity of droughts, the impacts of the groundwater table (GWT) depth and capillary rise on topsoil moisture may become critical drivers of biological activity. Consequently, the GWT depth could influence topsoil carbon (C) mineralization. In this study, undisturbed 200 cm long soil colu...

Substantial input of exogenous organic matter (EOM) may be required to offset the projected decline in soil organic carbon (SOC) stocks in croplands caused by global warming. However, information on the effectivity of the EOM application dose in preserving SOC stocks is surprisingly limited. Therefore, we set up a 90 d incubation experiment with la...

Sustainable cropland management requires preservation of soil organic matter (SOM). In spite of in depth understanding gained from ample field and laboratory studies, we have a poor understanding of landscape scale spatial variation of fresh organic matter (OM) decomposition and its conversion into soil organic carbon (SOC). Particularly, local top...

In the Vietnamese Mekong Delta, soil quality and crop yield are steadily declining under rice monocultures with three crops per year. The objective of this study was to evaluate the medium-term effects of rotating rice with upland crops and adding organic amendments on rice yield, and to relate this to soil quality. A field trial with split-plot de...

In the Vietnamese Mekong delta, soil quality and crop yield are steadily declining under rice monocultures with three crops per year. The objective of this study was to evaluate the medium-term effects of rotating rice with upland crops and adding organic amendments on rice yield and relate it to soil quality. A field trial with split-plot design i...

With climate change expected to intensify the occurrence and severity of droughts, the control of groundwater table (GWT) depth and capillary rise on topsoil moisture may render a critical driver of biological activity. Consequently, GWT depth could influence topsoil carbon mineralization. In this study, undisturbed 200 cm long soil columns of thre...

Substantial input of exogenous organic matter (EOM) may be required to offset the projected decline in soil organic carbon (SOC) stocks in croplands caused by global warming. However, information on the effectivity of EOM application dose in preserving SOC stocks is surprisingly limited. Therefore, we set up a 90-day incubation experiment with larg...

Soil nematodes are the most abundant soil fauna, with a potential great impact on soil N mineralization via interaction with soil microorganisms. As a consequence, nematodes likely also influence soil N2O production and emission but the very few studies on this matter were carried out in simplified setups with single nematode species and in (highly...

The untapped potential for carbon sequestration in agricultural soils represents one of the most cost-effective tools for climate change mitigation. Increasing soil organic matter also brings other agronomic benefits such as improved soil structure, enhanced water-and-nutrient-retention capacity, and biological activity. Broadly, soil organic carbo...

Land use is recognized to impact soil geochemistry on the centennial to millennial timescale, with implications for the distribution and stability of soil organic carbon (SOC). Young volcanic soils in tropical areas are subject to much faster pedogenesis, noticeable already on the centennial or even decadal timescale. As land use is a recognized fa...

Soil texture plays a crucial role in organic matter (OM) mineralization through both direct interactions with minerals and indirect effects on soil moisture. Separating these effects could enhance the modelling of soil organic carbon (SOC) dynamics under climate change scenarios. However, the attempts have been limited small-scale experiments. Here...

The occurrence and spread of invasive woody species are a truly global phenomenon, but tropical regions seem to be particularly vulnerable due to high rates of soil degradation in combination with climate change, and limited resources for containment. There is increasing awareness that complete eradication programs are often not efective. The exist...

Sterilization (partial or full) is one of the most fundamental tools for studying the ecological roles of soil biota and notably soil fauna, but there is a lack of knowledge on how these techniques affect other soil- inhabiting micro-organisms (non-target), and on their recovery after sterilization. We investigated the effect of a partial soil ster...

Soil mesofauna play an essential role in soil functioning. However, in studies on the impact of agricultural management on soil quality, the overall abundance of soil mesofauna and specific groups thereof has not been widely used as an indicator in developing countries. Here, we used soil mesofauna as a soil quality indicator compared to more tradi...

Biochar amendment of soil may ameliorate inherently infertile soils, such as in the typical coconut ( Cocos nucifera L.) growth areas along tropical coasts, where, moreover, temporary moisture stress commonly occurs. We conducted a pot experiment to evaluate the effects of biochar soil amendment (1% w/w) produced from Gliricidia sepium stems (BC-Gl...

We investigated changes in geochemical soil properties in response to deposition age and land use management over 30 – 50 years on tropical volcanic soils. Our purpose was to find out how weathering stage and land use interactively affect soil properties and organic carbon, and to check if phenoforms (management-related soil subtypes) exist within...

The addition of exogenous organic matter (EOM) generally stimulates microbial activity and shapes soil structure, likely with stronger effects at a higher application dose. It is not known, however, if and how the application dose of EOM would impact its own mineralisation and that of native soil organic carbon (SOC) by such mediation of soil pore...

Soil texture determines the location of moisture in the soil matrix. At lower moisture content, the contact between soil water and particulate organic matter (POM) might be critical for POM mineralization, because such areas of contact could function as a ‘bridge’ for transport of moisture, substrates, enzymes and microorganisms. Additionally, wate...

The drumbeat to reach net-zero emissions by 2050 and foster a European circular economy has arguably thrust anaerobic digestion front and centre due to its ability to produce renewable energy and fertilisers from recycled nutrients in the form of digestate. In this context, it is of paramount importance to better understand the fate of the nitrogen...

Research on microplastics (MP) in soils is much complicated due to the lack of dedicated (extraction) methodologies and the strong matrix interferences for MP detection, and there is almost no research on the dynamics of the smallest MP in soil. Here we compared the possible detection of the smallest MP fraction (1-2 µm) by µ-Raman spectroscopy and...

Land use is recognized to impact soil geochemistry on the centennial to millennial time scale, with implications for the distribution and stability of soil organic carbon (SOC). Juvenile volcanic soils in tropical areas are subject to much faster pedogenesis, with then also possibly a significant mediation by land use on much shorter centennial or...

The carbon (C) and nitrogen (N) mineralisation rates of five digestates were studied and compared with pig slurry, compost, and a solid fraction of digestate in aerobic incubation experiments. The objective was to identify the most relevant drivers of C and N mineralisation based on the physicochemical properties of the products. Net organic nitrog...

Soil organic carbon (SOC) levels generally increase with increasing clay and silt content under similar climatic conditions because of increased physicochemical protection. Surprisingly though, many silt loam soils in Western Europe have low top SOC levels compared to coarser textured soils. Soil texture also strongly controls soil moisture with co...

Soil phosphorus (P) leaching is one of the major causes of diffuse P losses towards the environment in north-west Europe. In order to cut back these P losses over the long term, soil P stocks need to be drastically reduced. Greenhouse experiments have shown that a rapid reduction of the plant available P pool is attained by reducing the P fertilize...

Abiotic fixation and defixation of ammonium (NH4+) in silicate interlayers are common processes in paddy soils, owing to their often high levels of 2:1 type clay minerals. Fixed NH4+ hence forms a buffer during the supply and loss of plant-available N. The soil redox potential (Eh) is suspected to influence NH4+ (de)fixation by its impact on the ne...

Termites can play a localized prominent role in soil nutrient availability and cycling because mound materials are often enriched in nutrients relative to surrounding soil. Mound materials may thus prove to be useful amendments, though evidently mound spatial arrangement needs to be considered as well. Furthermore, it is not known if gradients of s...

In the verge finding a sustainable solution to improve the fertility status of coconut growing soils of Sri Lanka, application of Biochar as a soil conditioner/soil amendment to improve low fertile soils is identified as a potential solution. The biochar for this research is produced from farm based waste materials using farmer-scale level biochar...

Although the amendment of various forms of exogenous organic matter (EOM) is a common practice in cropland production, it is to date not clear if its mineralisation in soil depends on application rate. Previous research suggested that spatial concentration of EOM in soil positively impacts its degradability. Here, we seek to test these reports and...

Anaerobic decomposition of organic carbon (OC) in submerged rice paddies is coupled to the reduction of alternative soil electron acceptors, primarily Fe3+. During reductive dissolution of Fe3+ from pedogenic oxides, previously adsorbed native soil organic carbon (SOC) could be co-released into solution. Incorporation of crop residues could hence i...

The separate and collective role of soil nematodes and protists at community level in soil biogeochemical processes remains poorly quantified due to the lack of appropriate methodologies to study them independently from other soil biota under conditions emulating natural soil. Here we present a methodological exploration for the selective removal o...

Inherent low fertility status of coconut grown soils, and the prolonged conventional farming practices without giving attention to the biological fertility component of coconut plantations, have resulted in inactive, degraded soils with very poor soil fertility. Soil microorganisms are a diverse group, having the ability to maintain the continuous...

Long-term field experiments have confirmed belowground plant carbon (C) to be two to three times more efficient precursor of soil organic carbon (SOC) than aboveground plant residues. But it remains elusive just when this belowground biomass is relatively stabilized against mineralization: during the initial fast degradation, or on the longer term?...

Soil organic carbon (OC) levels generally increase with increasing clay and silt content under a similar climatic zone because of increased association of OC to clay minerals and stronger occlusion inside aggregates. Surprisingly though, in Western Europe many silt loam soils actually bear low topsoil OC levels compared to lighter textured soils. S...

Anaerobic decomposition of organic carbon (OC) in submerged rice paddies is coupled to the reduction of alternative soil electron acceptors, primarily Fe3+. During reductive dissolution of Fe3+ from pedogenic oxides, previously adsorbed native soil organic carbon (SOC) could be co-released into solution. Incorporation of crop residues could hence i...

Purpose This study investigated the C and N mineralisation potential of solid fractions (SFs) from co-digestated pig manure after P-stripping (P-POOR SF) in comparison with P-rich SFs, as a means to estimate their organic matter stability in soil. Compost (COMP) and biochar (BCHR) (made from P-POOR SF) were also included in the study as reference...

Degradability of organic matter (OM) in soil depends on its spatial location in the soil matrix. A recent breakthrough in 3D-localization of OM combined dual-energy X-ray CT-scanning with OsO 4 staining of OM. The necessity for synchrotron-based µCT and the use of highly toxic OsO 4 severely limit applications in soil biological experiments. Here,...

Soil texture is well known to directly affect bioavailability of organic matter to heterotrophs, but it also steers their activity by moderating soil moisture fluctuation. Disentangling these direct and indirect textural controls is, however, not trivial and attempts to do so are very scarce. Most attention has just gone to the stimulation of soil...

The few available studies on maize biomass in soil of field experiments have shown that belowground maize biomass resides more than twice as long as aboveground residues. Our principal objective was to investigate the effect of maize crop residue incorporation on the long-term dynamics of soil organic carbon (SOC) for a selection of croplands with...

Knowledge about the response of root biomass and root system architecture (RSA) to soil conditions would increase efficiency in selecting high performance crop varieties and predicting the impact of rotations on long-term soil organic matter (SOM) stock. We evaluated the effect of variety and site on maize (Zea mays L.) root growth. Two-dimensional...

Agriculture is estimated to generate about 700 million tons of waste annually in the EU. Novel valoriza-tion technologies are developing continuously to recover and recycle valuable compounds and nutrients from waste materials. To close the nutrient loop, low-value agri-food wastes, co-products and by-products (AFWCBs) produced during the valorizat...

Increasing interest in plant-root phenotyping has stimulated the development of X-ray μCT-based root/soil segmentation protocols. However, most scanning and CT volume processing protocols were only applied for detection of simple and small juvenile roots. We tested a new methodology for its ability to extract large mature maize roots from X-ray μCT...

Soil amendment with biochar can modify soil microbial abundance, activity and community structure. Nevertheless, the long-term evolution of these effects is unknown and of critical importance because biochar persists in soil for centuries. We selected nine charcoal kiln sites (CKS) from forests (four sites) and croplands (five sites) and determined...

Evidence is accumulating that belowground crop residues contribute more efficiently to the build‐up and maintenance of native soil organic carbon (SOC) than aboveground plant parts. We corroborated previous testing of the hypothesis that root‐C would preferentially accumulate in soil microaggregates, where it is physically protected against microbi...

Soil organic carbon (SOC) plays a vital role in soil fertility and quality, resilience against degradation, and consequently food security. Therefore, it is crucially important to understand how current SOC stocks will be affected under future climate change scenarios. Silt soils in Western-Europe have superior soil physical quality but have lower...

Soil moisture strongly affects the balance between nitrification, denitrification and N2O reduction and therefore the nitrogen (N) efficiency and N losses in agricultural systems. In rice systems, there is a need to improve alternative water management practices, which are designed to save water and reduce methane emissions but may increase N2O and...

The rising demand for feed and food has put an increasing pressure on agriculture, with agricultural intensification as a direct response. Notwithstanding the higher crop productivity, intensive agriculture management entails many adverse environmental impacts. Worldwide, soil organic carbon (SOC) decline is hereby considered as a main danger which...

Soil moisture strongly affects the balance between nitrification, denitrification and N2O reduction and therefore the nitrogen (N) efficiency and N losses in agricultural systems. In rice systems, there is a need to improve alternative water management practices, which are designed to save water and reduce methane emissions, but may increase N2O an...

Mineral nitrogen (N) availability to heterotrophic micro-organisms is known to impact organic matter (OM) decomposition. Different pathways determining the N accessibility depend to a large extent on soil structure. Contact between soil mineral and OM substrate particles can facilitate N transport toward decomposition hot spots. However, the impact...

There is increasing pressure to reduce water use in irrigated rice production to save water, reduce methane emissions and reduce grain arsenic uptake arising from anaerobic conditions. However, under such practices emissions of nitrous oxide (N2O) often increase. Rice systems generally exhibit strong stratification of environmental conditions that...

Paddy soil indigenous N supply is often poorly related to N status and our aim was to assess its linkage to reduction of Fe3+ and Mn4+, primary terminal electron acceptors in submerged soils. Transplanted rice was grown in the greenhouse in four Bangladeshi paddy soils with distinct SOC to Feox ratio (1.6 to 4.9) for 72days firstly under continuous...

In rice production, water-saving irrigation management is expanding and likely alters depth profiles of soil moisture, redox potential (Eh) and microbial activity. It is, however, unclear how such conditions then impact net soil N-release and availability to the rice crop, because we do not know well enough how water-saving irrigation management sh...

In rice production, water-saving irrigation management is expanding and likely alters depth profiles of soil moisture, redox potential (Eh) and microbial activity. It is, however, unclear how such conditions then impact net soil N-release and availability to the rice crop, because we do not know well enough how water-saving irrigation management sh...

Nitrogen (N) depositions in Europe are decreasing, but this could not explain faster than expected improvement of N saturation indicators in temperate forests. Alongside there were local signs of initial recovery from acidification during the past three decades and enhanced leaching of dissolved organic carbon and nitrogen (DOC, DON). These two glo...

Historic long-term P application to sandy soils in NW-Europe has resulted in abundant sorption, saturation and eventually leaching of P from soil to the groundwater. Although many studies recognize the control of site-specific factors like soil texture and phosphate saturation degree (PSD), the regional-scaled relevance of effects exerted by single...

Over the past decade analysis of multiple field experiments has proven that belowground biomass contributes twice more than aboveground biomass to build-up and preservation of soil organic matter (SOM). Alongside, a consensus has emerged that model based predictions are particularly ill-parameterized for amount and degradability of belowground biom...

Classical nitrogen (N) mineralization experiments are done using uncropped soil, thus completely neglecting the influence of roots and root exudates. Therefore, experiments were conducted at two field sites in Bangladesh during 'boro' season (winter rice), using two rice cultivars (BRRI Dhan 29 and BINA Dhan6) to investigate the influence of rice r...

We evaluated trends (2005–2013) and patterns of dissolved organic nitrogen (DON) and its ratio with dissolved organic carbon (DOC), DOC:DON in atmospheric deposition and soil solution of five Level II plots of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) in Flanders, Norther...

To understand the roles of nematodes in organic matter (OM) decomposition, experimental setups should include the entire nematode community, the native soil microflora, and their food sources. Yet, published studies are often based on either simplified experimental setups, using only a few selected species of nematode and their respective prey, des...

The hazard for recurring food insecurity in the Sahel is largely affected by insufficient biomass productivity of degraded, marginal lands. In general, Water and Soil Conservation (WSC) techniques are believed to tackle the deterioration of soil quality by enhancing soil hydraulic properties, soil life and soil organic carbon content (SOC), but thi...

In the Mekong Delta, alluvial clay soils have been used intensively over many generations for rice monoculture. Currently, farmers are confronted by problems of declining land productivity. Rotations comprising rice and upland crops can increase soil quality, but appropriate cropping systems for paddy soils have received relatively little attention...

Most studies looking into the effect of amendment of biochar on soil microbial functioning employ shortterm laboratory studies and probably describe relatively transient phenomena. Multi-year experiments, spanning beyond initial degradation of biologically labile biochar constituents, on the other hand are more scarce, although these are much neede...

The majority of microbial mediated soil processes depend on availability of organic matter (OM), water and air. Because of its ability to visualize the 3D architecture of soil non-destructively, X-ray computed tomography (CT) is becoming a widespread tool for studying soil pore network structure. However, phase determination of pore space, soil OM,...

Soil organic N is largely composed of inherently biologically labile proteinaceous N and its persistence in soil is mainly explained by stabilization through binding to minerals and other soil organic matter (SOM) components at varying strengths. In order to separate kinetically different soil N fractions we hypothesize that an approach which isola...

Four biochar types, produced by slow pyrolysis of poultry litter (PL) and pine chips (P) at 400 or 500 °C, were added to two adjacent soils with contrasting soil organic matter (SOM) content (8.9 vs. 16.1 g C kg−1). The N mineralization rate was determined during 14-week incubations and assessments were made of the microbial biomass C, dehydrogenas...

Soil organic N is largely composed of inherently biologically labile proteinaceous N and its persistence in soil is mainly explained by stabilization through binding to minerals and other soil organic matter (SOM) components at varying strengths. In order to separate kinetically different soil N fractions we hypothesize that an approach, which isol...

Anaerobic N mineralization measured from (saturated) repacked soil cores from 25 paddy fields in Bangladesh and was previously found to negatively related to soil N content on a relative basis. This suggests that other factors like soil organic matter (SOM) quality or abiotic factors instead control the anaerobic N mineralization process. We theref...

Soil organic nitrogen mineralization rates and possible predictors thereof were investigated for vegetable-growing soils in Belgium. Soil organic matter (SOM) was fractionated into sand (> 53 μm) and silt+clay (< 53 μm) fractions. The latter fraction was further separated into 6%NaOCl-oxidation labile (6%NaOCl-ox) and resistant N and C and subseque...

Soil pore network effects on organic matter turnover have, until now, been studied indirectly because of lack of data on the 3D structure of the pore network. Application of X-ray computed tomography (X-ray CT) to quantify the distribution of pore neck size and related pore sizes from undisturbed soil cores, with simultaneous assessment of carbon (...

The nitrogen (N) requirement for paddy rice cultivated in Bangladesh amounts to approximately 80 kg N ha−1. Lack of knowledge on N mineralization from soil organic matter leads farmers to meet this N requirement exclusively by costly mineral fertilizers, which have typically an efficiency of less than 40%. We assessed to what extent routinely analy...

Biochar produced during pyrolysis of biomass has the potential to reduce greenhouse gas (GHG) emissions from soils. In order to evaluate the effect of four different biochar additions on the emission of the greenhouse gases CO2 and N2O, two incubation experiments were established in a temperate sandy loam soil. Digestate, a waste-product of the wet...

Combining X-ray micro-Computed Tomography (X-ray micro-CT) analysis with measures of soil microbial functioning would provide a powerful tool for revealing the influence of soil pore structure on soil organic matter (SOM) decomposition. We investigated the impact of X-ray micro-CT scanning on soil microbial functioning for the first time by assessi...

The influence of three main groups of low molecular weight organic substances (LMWOS) commonly exuded by plant roots into the rhizosphere such as amino acids (AA), carbohydrates (CHYD) and carboxylic acids (CA) on nitrogen mineralization of a loamy soil from Bangladesh were studied under laboratory condition at 25°C for 14 days in a simulated rhizo...

Soil organic matter (SOM) quality and its decomposability are influenced by cropping pattern. In particular, little is known on the specific difference in SOM quality under rice monoculture or combination of vegetables with rice culture. Therefore, four pairs of fields having vegetable-rice and rice-rice cropping pattern were selected from four dif...

The influence of three main groups of low molecular weight organic substances (LMWOS) commonly exuded by plant roots into the rhizosphere such as amino acids (AA), carbohydrates (CHYD) and carboxylic acids (CA) on nitrogen mineralization of a loamy soil from Bangladesh were studied under laboratory condition at 25°C for 14 days in a simulated rhizo...

We explored the value of ergosterol, phospholipid fatty acid (PLFA) profiles and neutral lipid fatty acid (NLFA) 16:1ω5c as soil quality indicators for the intensive systems of vegetable production in the humid tropical climate of West Java, by comparing organic and conventional management. Additionally, we measured dehydrogenase and β-glucosidase...

Eight fertilization strategies were compared in a field trial on Alfisol in Belgium (humid temperate climate): cattle slurry (CSL); farmyard manure (FYM); vegetable, fruit and garden waste compost (VFG); high C/N farm compost (FCP1); low C/N farm compost (FCP2); exclusively mineral fertilizer (MIN N); no fertilization (NF+), no fertilization and no...

Intensive vegetable production systems throughout South East Asia are characterised by large nutrient inputs and low nitrogen (N) use efficiencies. In Indonesia, intensive vegetable production is concentrated on volcanic highland soils starting from an altitude of around 700 m above sea level. We measured potential N mineralisation from soil organi...

Conservation agriculture (CA) character-ised by minimal soil disturbance, permanent soil surface cover by dead or living plants and crop rotations is one way of achieving higher soil organic carbon (C) in agricultural fields. Sandy loam and loamy soil samples from zero tillage (ZT) and conventional tillage (CT) plots were taken from farmers' fields...