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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Plant trait-based approaches to improve nitrogen cycling in agroecosystems
Abalos, Diego ; Groenigen, Jan Willem van; Philippot, Laurent ; Lubbers, Ingrid M. ; Deyn, Gerlinde B. De - \ 2019
Journal of Applied Ecology (2019). - ISSN 0021-8901
agroecosystems - fertilizer - functional traits - nitrogen cycling - nitrogen losses - plant mixtures - plant traits - plant–soil interactions

Intensive agriculture is dominated by monocultures of high-yielding plants that receive large applications of nitrogen (N) fertilizers to boost plant productivity. However, these systems have low N use efficiency (NUE) as fertilized plants generally take up less than half of the N applied. A large fraction of the remainder N is susceptible to be lost from the agroecosystem generating a cascade of environmental and socio-economic problems. Climate change and projected global increases in fertilizer use pose further risks to N losses and yield stability. We review and translate concepts from ecology in natural systems to demonstrate that NUE in intensive agroecosystems can be strongly increased by fine-tuning the traits of the plant communities to the levels of N fertilization intensity. We present key plant traits of importance for N-cycling (architectural, morphological and physiological traits, as well as symbiotic associations and exudation patterns); discuss ecological (with soil fauna and N-cycling microbial communities) and agronomic interactions of this approach; propose interdisciplinary methodologies for future research ranging from pot to global scales; and highlight possible solutions leading to an optimal balance between N fertilizer use and productivity. Synthesis and applications. By showing the strong links between plant traits and nitrogen (N) cycling, our work opens possibilities to test ecologically informed hypotheses across gradients of soil fertility and N fertilizer management intensity, setting a research agenda for the coming years. Accordingly, the choice of plant species based on their functional traits will play a central role for the development of modern and productive agroecosystems that retain and use N more efficiently.

How fertile are earthworm casts? A meta-analysis
Groenigen, J.W. van; Groenigen, Kees Jan van; Koopmans, G.F. ; Stokkermans, Lotte ; Vos, M.J. ; Lubbers, I.M. - \ 2019
Geoderma 338 (2019). - ISSN 0016-7061 - p. 525 - 535.
It has long been established that earthworms beneficially affect plant growth. This is to a large extent due to the high fertility of their casts. However, it is not clear how fertile casts are compared to bulk soil, and how their fertility varies between earthworm feeding guilds and with physico-chemical soil properties. Using meta-analysis, we quantified the fertility of earthworm casts and identi
fied its controlling factors. Our analysis included 405 observations from 81 articles, originating from all continents except Antarctica. We quantified cast fertility by determining the enrichment of earthworm casts relative to the bulk soil (“relative cast fertility”; RCF) for total organic carbon (TOC), total phosphorus (P) and total nitrogen (N) concentrations, as well as for plant available pools of N (total mineral N) and P (available P: P-Olsen, P-Bray or comparable metrics), C-to-N ratio and microbial biomass C. In addition to these response variables, we studied four additional ones closely related to soil fertility: pH-H2O, clay content, cation exchange capacity (CEC), and base saturation. With the exception of C-to-N ratio, microbial C and clay content, all studied response variables were significantly increased in casts compared to the bulk soil. Increases in total elemental concentrations (TOC, total P and total N), which are the result of preferential feeding or concentration processes, were comparable and ranged between 40 and 48%. Nutrient availability, which is to a large extent the result of (bio)chemical transformation processes in the earthworm gut, was increased more strongly than total elemental concentrations (241% and 84% for mineral N and available P, respectively). Increases in pH (0.5 pH units), cation exchange capacity (40%), and base saturation (27%) were also large and significant. None of the soil-related possible controlling factors could satisfactorily explain the
variation in RCF; plant presence (or other sources of organic C input such as residue application) was the only controlling factor that consistently increased RCF across soil properties. With the exception of available P, none of the studied response variables could be linked to earthworm feeding guild. Our results show that earthworm casts are much more fertile than bulk soil for almost all analysed cast fertility properties. However, these positive RCFs are to a large extent dependent upon the presence of plants. In general, earthworm feeding guild or specific physico-chemical soil properties could not explain the large variability in RCF for the various response variables. Therefore, we hypothesize that RCF e
ffects depend on intricate interactions between earthworm species traits and specific soil properties. Understanding these interactions requires trait-based approaches combined with mechanistic modelling of biochemical processes in the earthworm gut and casts.
Framboos: van inhoudsstof tot hype
Beekwilder, Jules - \ 2018

De consumptie van frambozen zit nog altijd in de lift. Maar hoe is de framboos eigenlijk op de kaart gezet? Biochemisch onderzoeker Jules Beekwilder van de Wageningen University & Research (WUR) heeft het van dichtbij meegemaakt en volgt de framboos nog altijd. Ruim 10 jaar geleden publiceerde hij dat frambozen een heel speciaal stofje in vrij grote hoeveelheden aanmaken. Het is in bijna geen ander fruit te vinden maar aan dat stofje, ellagitannine, worden wel super gezonde en medicinale eigenschappen toegedicht.

Can earthworms simultaneously enhance decomposition and stabilization of plant residue carbon?
Lubbers, Ingrid M. ; Pulleman, Mirjam M. ; Groenigen, Jan Willem van - \ 2017
Soil Biology and Biochemistry 105 (2017). - ISSN 0038-0717 - p. 12 - 24.
Aporrectodea caliginosa - CO emission - Lumbricus rubellus - Maize residues - Multi-year experiment - Soil organic matter

Earthworm activity can strongly influence soil structure and organic matter (OM) dynamics of agricultural soils. Several short-term studies (≤90 days) have shown that earthworms can increase incorporation of residue carbon (C) into soil aggregates, suggesting reduced decomposition in the longer term. In contrast, another body of short-term studies reported that earthworms can increase carbon dioxide (CO2) emission from soils, thus suggesting increased decomposition in the longer term instead. To solve this controversy, we measured the effect of the epigeic Lumbricus rubellus (Hoffmeister) and the endogeic Aporrectodea caliginosa (Savigny) on the soil C balance in a unique 750-day mesocosm experiment, where loess soil was surface-applied with maize (Zea mays L.) residues every six months. Carbon inputs and outputs were strictly controlled: no soil C input through growing plants and no leaching of soil organic C. Flux measurements of CO2 were taken regularly and aggregate size distribution and total C and residue-derived C in the aggregate fractions (using the natural δ13C signature of maize) were measured after 185, 565 and 750 days. Both earthworm species increased cumulative CO2 emissions by at least 25%, indicating a higher C loss compared to the no-earthworm control. Yet, both earthworm species also increased the amount of soil C associated with the macroaggregate fraction after 750 days. L. rubellus increased the amount of residue-derived C in the macroaggregate fraction after 565 and after 750 days, whereas A. caliginosa increased residue-derived C in all the measured soil fractions after 750 days. Our results show that earthworms can simultaneously enhance CO2 emissions and C incorporation in aggregate fractions. However, over 750 days the presence of earthworms resulted in a lower total C content due to a higher overall OM decomposition rate. We therefore propose that under the most realistic incubation conditions so far (longer term and multiple residue applications), earthworms stimulate the mineralization of freshly added and older OM to a greater extent than that they stabilize residue-derived C inside biogenic aggregates. Future studies should focus on the balance between these processes in the presence of growing plants.

Mining for Gold: Large Scale Data Management and Analysis of on-Farm Legume Trials
Heerwaarden, J. van; Lubbers, M.T.M.H. - \ 2016
In: Book of abstracts Joint Pan-African Grain Legume and World Cowpea Conference. - - p. 93 - 93.
Op reis in de bodem
Deyn, Gerlinde de; Lubbers, Ingrid ; Groenigen, Jan-Willem van - \ 2016

In de kelder van Atlas leggen camera’s met timelapsefotografi e de wording van planten vast. Voor het eerst tegelijk boven en onder de grond. Het project is gesponsord door de ‘crowd’.

Mining for gold: large scale data management and analysis of on-farm legume trials : N2Africa - Putting nitrogen fixation to work for smallholder farmers in Africa
Heerwaarden, J. van; Lubbers, M.T.M.H. ; Adjei-Nsiah, S. ; Bayukija, F. ; Ebanyat, P. ; Kamai, Nkeki ; Sangodele, E. ; Wolde-Meskel, E. ; Abdulkadir, Birhan ; Amppiah, Arnold ; Epel, A. ; Mzandah, A. ; Muhammad, S. ; Ukem, B. ; Onyinge, J. ; Othieno, A. ; Sekham, J. ; Ampadu-Boakye, Theresa ; Franke, L. - \ 2016
Engaging farmers on climate risk through targeted integration of bio-economic modelling and seasonal climate forecasts
Nidumolu, U.B. ; Lubbers, M. ; Kanellopoulos, A. ; Ittersum, M.K. van; Kadiyala, D.M. ; Sreenivas, G. - \ 2016
Agricultural Systems 149 (2016). - ISSN 0308-521X - p. 175 - 184.
Climate risk - Crop choice - Mathematical programming - Probabilistic seasonal forecasts - Profit maximisation - Small holder farmers

Seasonal climate forecasts (SCFs) can be used to identify appropriate risk management strategies and to reduce the sensitivity of rural industries and communities to climate risk. However, these forecasts have low utility among farmers in agricultural decision making, unless translated into a more understood portfolio of farm management options. Towards achieving this translation, we developed a mathematical programming model that integrates seasonal climate forecasts to assess ‘what-if?’ crop choice scenarios for famers. We used the Rayapalli village in southern India as a case study. The model maximises expected profitability at village level subject to available resource constraints. The main outputs of the model are the optimal cropping patterns and corresponding agricultural management decisions such as fertiliser, biocide, labour and machinery use. The model is set up to run in two steps. In the first step the initial climate forecast is used to calculate the optimal farm plan and corresponding agricultural management decisions at a village scale. The second step uses a ‘revised forecast’ that is given six weeks later during the growing season. In scenarios where the forecast provides no clear expectation for a dry or wet season the model utilises the total agricultural land available. A significant area is allocated to redgram (pigeon pea) and the rest to maize and paddy rice. In a forecast where a dry season is more probable, cotton is the predominant crop selected. In scenarios where a ‘normal’ season is expected, the model chooses predominantly cotton and maize in addition to paddy rice and redgram. As part of the stakeholder engagement process, we operated the model in an iterative way with participating farmers. For ‘deficient’ rainfall season, farmers were in agreement with the model choice of leaving a large portion of the agriculture land as fallow with only 40 ha (total area 136 ha) of cotton and subsistence paddy rice area. While the model crop choice was redgram in ‘above normal and wet seasons, only a few farmers in the village favoured redgram mainly because of high labour requirements, and the farmers perceptions about risks related to pests and diseases. This highlighted the discrepancy between the optimal cropping pattern, calculated with the model and the farmer's actual decisions which provided useful insights into factors affecting farmer decision making that are not always captured by models. We found that planning for a ‘normal’ season alone is likely to result in losses and opportunity costs and an adaptive climate risk management approach is prudent. In an interactive feedback workshop, majority of participating farmers agreed that their knowledge on the utility and challenges of SCF have highly improved through the participation in this research and most agreed that exposure to the model improved their understanding of the role of SCF in crop choice decisions and that the modelling tool was useful to discuss climate risk in agriculture.

The Zn2Cys6 transcription factor BcGaaR regulates D-galacturonic acid utilization in Botrytis cinerea
Zhang, Lisha ; Lubbers, Ronnie ; Simon, Adeline ; Stassen, J.H.M. ; Vargas Ribera, Pablo ; Viaud, Muriel ; Kan, J.A.L. van - \ 2016
BioSpektrum (2016)Tagungsband. - ISSN 0947-0867 - p. 116 - 116.
A novel Zn2Cys6 transcription factor BcGaaR regulates D-galacturonic acid utilization in Botrytis cinerea
Zhang, Lisha ; Lubbers, Ronnie J.M. ; Simon, Adeline ; Stassen, Joost H.M. ; Vargas Ribera, Pablo R. ; Viaud, Muriel ; Kan, Jan A.L. van - \ 2016
Molecular Microbiology 100 (2016)2. - ISSN 0950-382X - p. 247 - 262.

Summary: D-galacturonic acid (GalA) is the most abundant monosaccharide component of pectin. Previous transcriptome analysis in the plant pathogenic fungus Botrytis cinerea identified eight GalA-inducible genes involved in pectin decomposition, GalA transport and utilization. Co-expression of these genes indicates that a specific regulatory mechanism occurs in B. cinerea. In this study, promoter regions of these genes were analysed and eight conserved sequence motifs identified. The Bclga1 promoter, containing all these motifs, was functionally analysed and the motif designated GalA Responsive Element (GARE) was identified as the crucial cis-regulatory element in regulation of GalA utilization in B. cinerea. Yeast one-hybrid screening with the GARE motif led to identification of a novel Zn2Cys6 transcription factor (TF), designated BcGaaR. Targeted knockout analysis revealed that BcGaaR is required for induction of GalA-inducible genes and growth of B. cinerea on GalA. A BcGaaR-GFP fusion protein was predominantly localized in nuclei in mycelium grown in GalA. Fluorescence in nuclei was much stronger in mycelium grown in GalA, as compared to fructose and glucose. This study provides the first report of a GalA-specific TF in filamentous fungi. Orthologs of BcGaaR are present in other ascomycete fungi that are able to utilize GalA, including Aspergillus spp., Trichoderma reesei and Neurospora crassa. Short Abstract: The transcriptional regulator that controls D-galacturonic acid (GalA) utilization in fungi was unknown. We identified in Botrytis cinerea a novel Zn2Cys6 transcription factor (TF), designated BcGaaR, which is required for the induction of GalA-utilization genes. The BcGaaR protein was predominantly localized in nuclei in cultures grown on GalA, but remained in the cytoplasm in cultures grown on glucose. This study provides the first report of a GalA-specific TF in filamentous fungi. Orthologs of BcGaaR are present in other ascomycete fungi that are able to utilize GalA, including Aspergillus spp., Trichoderma reesei and Neurospora crassa.

Exploring the relationship between soil mesofauna, soil structure and N2O emissions
Porre, R.J. ; Groenigen, J.W. van; Deyn, G.B. de; Goede, R.G.M. de; Lubbers, I.M. - \ 2016
Soil Biology and Biochemistry 96 (2016). - ISSN 0038-0717 - p. 55 - 64.
Agricultural soils are a large source of nitrous oxide (N2O) emissions. Soil mesofaunal species can accelerate, delay, increase or decrease N2O emissions. However, it is still unknown whether the soil fauna affect N2O emissions through trophic interactions or through their effect on soil structure. We explored the role of these two pathways in a 70 day microcosm experiment with a sandy loam subsoil with hay mixed in. Enchytraeids, fungivorous mites and predatory mites were added to the soil in a full factorial design to test for both single species effects as well as interactions between species. We measured N2O and CO2 fluxes and we analysed soil structural parameters using X-ray micro tomography. After 35 days of incubation, enchytraeid presence significantly increased the volumetric air content of the soil (0.049–0.067 cm3 cm−3, P = 0.010) as well as the abundance of pores with sizes similar to their body width. At the same time N2O emissions, −NO3NO3− and DOC concentrations were significantly higher when enchytraeids were present (3.6 to 8.4 mg N2O-N m−2, P < 0.001; 6.0 to 17.1 mg −NO3-NNO3−-N kg−1 soil, P < 0.001; 121.1 to 135.6 mg C kg−1 soil, and P = 0.017, respectively). Neither fungivorous mites nor predatory mites nor their interactions had a significant effect on soil structure or N2O emissions. Enchytraeids accelerated peak N2O emissions (P = 0.001), but did not increase cumulative N2O emissions on day 70. Structural equation modelling confirmed that enchytraeids enhanced nitrogen mineralisation directly and also indirectly by creating a higher volumetric air content, and thereby increased N2O emissions. We conclude that the soil structure pathway was important in driving N2O emissions, and that soil ecosystem engineers such as enchytraeids disproportionately affected N2O emissions as compared to other soil fauna.
Reduced greenhouse gas mitigation potential of no-tillage soils through earthworm activity
Lubbers, I.M. ; Groenigen, K.J. van; Brussaard, L. ; Groenigen, J.W. van - \ 2015
Scientific Reports 5 (2015). - ISSN 2045-2322 - 10 p.
Concerns about rising greenhouse gas (GHG) concentrations have spurred the promotion of no-tillage practices as a means to stimulate carbon storage and reduce CO2 emissions in agro-ecosystems. Recent research has ignited debate about the effect of earthworms on the GHG balance of soil. It is unclear how earthworms interact with soil management practices, making long-term predictions on their effect in agro-ecosystems problematic. Here we show, in a unique two-year experiment, that earthworm presence increases the combined cumulative emissions of CO2 and N2O from a simulated no-tillage (NT) system to the same level as a simulated conventional tillage (CT) system. We found no evidence for increased soil C storage in the presence of earthworms. Because NT agriculture stimulates earthworm presence, our results identify a possible biological pathway for the limited potential of no-tillage soils with respect to GHG mitigation.
Trade-offs around the use of biomass for livestock feed and soil cover in dairy farms in the Alaotra lake region of Madagascar. Special Issue: Biomass use trade-offs in cereal cropping systems: Lessons and implications from the developing world
Naudin, K. ; Bruelle, G. ; Salgado, P. ; Penot, E. ; Lubbers, M.T.M.H. ; Ridder, N. de; Giller, K.E. - \ 2015
Agricultural Systems 134 (2015). - ISSN 0308-521X - p. 36 - 47.
cropping systems - conservation agriculture - physical-properties - zero-tillage - south-asia - residue - africa - maize - rice - productivity
Conservation agriculture (CA) is promoted as a promising technology to stabilize or improve crop yields in Africa and Madagascar. However, small-scale farmers face difficulties to retain soil cover, mainly because of competing uses for the biomass produced, especially to feed cattle. To explore the relation between dairy production and CA we developed an optimisation model at farm level. Our aim was to explore trade-offs between CA practices and the size of dairy cow herds. Our model includes three main components: the farm, the crops and the cattle herd. The optimisation was made on the total net income for three years. Biomass produced by cropping activities can either serve as mulch or to feed cows. We applied a constraint on the minimum soil cover % to keep at the end of each year for CA fields: from 30% to 95%. We simulated two scenarios of milk market: a small milk market with low forage price and an open milk market scenario with higher price of forage. Three prototypes of farms were simulated with different proportion and size of four kinds of field. These three prototypes were: medium-sized farm with hillsides dominating, medium-sized farm with paddy fields dominating and small-sized farm with hillsides. Changing the degree of soil cover to be retained on CA plots did not significantly modify the total net farm income. It was more strongly influenced by the characteristics of the milk market. In case of a limited milk market it was not profitable to have more than seven cows because the expenses were not compensated by animal production. When setting minimum soil cover to 30% then all of the simulated results include biomass coming from CA cropping system even with 12 cows/farm. Conversely when setting this constraint to 95%, above 6/7 cows/farm forage come only from conventional fields. In all of the situations simulated even with 6 cows, with the current and twice the price for forage, it was possible to keep at least 50% of soil cover on 30–60% of the total farm area. CA was not feasible for farms with no irrigated paddy fields or when forage fetched a high price regardless of the constraint for % of soil cover to be kept on CA fields. Overall, CA systems can be beneficial for dairy cow farmers due to the forage produced, although the milk market and thus the value of biomass for forage, has a strong influence on CA practice at field level.
The soil N cycle: new insights and key challenges
Groenigen, J.W. van; Huygens, D. ; Boeckx, P. ; Kuyper, T.W. ; Lubbers, I.M. ; Rutting, L. ; Groffman, P.M. - \ 2015
SOIL 1 (2015). - ISSN 2199-3971 - p. 235 - 256.
The study of soil N cycling processes has been, is, and will be at the centre of attention in soil science research. The importance of N as a nutrient for all biota; the ever-increasing rates of its anthropogenic input in terrestrial (agro)ecosystems; its resultant losses to the environment; and the complexity of the biological, physical, and chemical factors that regulate N cycling processes all contribute to the necessity of further understanding, measuring, and altering the soil N cycle. Here, we review important insights with respect to the soil N cycle that have been made over the last decade, and present a personal view on the key challenges of future research. We identify three key challenges with respect to basic N cycling processes producing gaseous emissions: 1. quantifying the importance of nitrifier denitrification and its main controlling factors; 2. characterizing the greenhouse gas mitigation potential and microbiological basis for N2O consumption; 3. characterizing hotspots and hot moments of denitrification Furthermore, we identified a key challenge with respect to modelling: 1. disentangling gross N transformation rates using advanced 15N / 18O tracing models Finally, we propose four key challenges related to how ecological interactions control N cycling processes: 1. linking functional diversity of soil fauna to N cycling processes beyond mineralization; 2. determining the functional relationship between root traits and soil N cycling; 3. characterizing the control that different types of mycorrhizal symbioses exert on N cycling; 4. quantifying the contribution of non-symbiotic pathways to total N fixation fluxes in natural systems We postulate that addressing these challenges will constitute a comprehensive research agenda with respect to the N cycle for the next decade. Such an agenda would help us to meet future challenges on food and energy security, biodiversity conservation, water and air quality, and climate stability.
Earthworms increase plant production: a meta- analysis
Groenigen, J.W. van; Lubbers, I.M. ; Vos, H.M.J. ; Brown, G.G. ; Deyn, G.B. de; Groenigen, K.J. van - \ 2014
Scientific Reports 4 (2014). - ISSN 2045-2322
ecosystem services - soil carbon - n pools - management - nitrogen - growth - agroecosystems - agriculture - communities - tolerance
To meet the challenge of feeding a growing world population with minimal environmental impact, we need comprehensive and quantitative knowledge of ecological factors affecting crop production. Earthworms are among the most important soil dwelling invertebrates. Their activity affects both biotic and abiotic soil properties, in turn affecting plant growth. Yet, studies on the effect of earthworm presence on crop yields have not been quantitatively synthesized. Here we show, using meta-analysis, that on average earthworm presence in agroecosystems leads to a 25% increase in crop yield and a 23% increase in aboveground biomass. The magnitude of these effects depends on presence of crop residue, earthworm density and type and rate of fertilization. The positive effects of earthworms become larger when more residue is returned to the soil, but disappear when soil nitrogen availability is high. This suggests that earthworms stimulate plant growth predominantly through releasing nitrogen locked away in residue and soil organic matter. Our results therefore imply that earthworms are of crucial importance to decrease the yield gap of farmers who can't -or won't- use nitrogen fertilizer.
Earthworms and the soil greenhouse gas balance
Lubbers, I.M. - \ 2014
Wageningen University. Promotor(en): Lijbert Brussaard, co-promotor(en): Jan-Willem van Groenigen. - Wageningen : Wageningen University - ISBN 9789461739315 - 222
aardwormen - oligochaeta - broeikasgassen - bodem - koolstofvastlegging in de bodem - koolstofvastlegging - emissie - bodembiologie - earthworms - oligochaeta - greenhouse gases - soil - soil carbon sequestration - carbon sequestration - emission - soil biology

Earthworms play an essential part in determining the greenhouse gas (GHG) balance of soils worldwide. Their activity affects both biotic and abiotic soil properties, which in turn influence soil GHG emissions, carbon (C) sequestration and plant growth. Yet, the balance of earthworms stimulating C sequestration on the one hand and increasing GHG emissions on the other has not been investigated. Indeed, much is still unclear about how earthworms interact with agricultural land use and soil management practices, making predictions on their effects in agro-ecosystems difficult. In this thesis, I aimed to determine to what extent GHG mitigation by soil C sequestration as affected by earthworms is offset by earthworm-induced GHG emissions from agro-ecosystems under different types of management. To reach this aim, I combined mesocosm and field studies, as well as meta-analytic methods to quantitatively synthesize the literature.

Using meta-analysis, I showed that, on average, earthworm activity leads to a 24% increase in aboveground biomass, a 33% increase in carbon dioxide (CO2) emissions and a 42% increase in nitrous oxide (N2O) emissions. The magnitude of these effects depends on soil factors (e.g., soil organic matter content), experimental factors (e.g., crop residue addition or fertilizer type and rate) and earthworm factors (e.g., earthworm ecological category and -density).

Conducting both a mesocosm and a field study, I showed that earthworm activity results in increased N2O emissions from fertilized grasslands. Under field conditions I found an increase in earthworm-induced N2O emissions in autumn but not in spring, suggesting that earthworm effects in the field depend on soil physicochemical parameters influenced by meteorological and seasonal dynamics.

In a unique two-year experiment with a simulated no-tillage (NT) system and a simulated conventional tillage (CT) system, I found that earthworm presence increases GHG emissions in an NT system to the same level as in a CT system. This suggests that the GHG mitigation potential of NT agro-ecosystems is limited. When considering the C budget in the simulated NT system, I demonstrated that over the course of the experiment earthworms increase cumulative CO2 emissions by at least 25%, indicating a higher C loss compared to the situation without earthworms. Yet, in the presence of earthworms the incorporation of residue-derived C into all measured soil aggregate fractions also increased, indicating that earthworm activity can simultaneously enhance CO2 emissions and C incorporation into aggregate fractions.

In conclusion, the revealed dominance of GHG emissions over C sequestration as affected by earthworms implies that their presence in agro-ecosystems results in a negative impact on the soil greenhouse gas balance.

TechnoGIN Quick start tutorial. EU version for long-term rotations (version 2).
Wolf, J. ; Lubbers, M.T.M.H. - \ 2013
Wageningen University - 32 p.
Earthworms can increase nitrous oxide emissions from managed grassland: a field study
Lubbers, I.M. ; López González, E. ; Hummelink, E.W.J. ; Groenigen, J.W. van - \ 2013
Agriculture, Ecosystems and Environment 174 (2013). - ISSN 0167-8809 - p. 40 - 48.
nitrifier denitrification - carbon-dioxide - n2o emission - crop residue - soil - fluxes - agroecosystem - mesocosms - peat - gut
Earthworms are important in determining the greenhouse gas (GHG) balance of soils. In laboratory studies they have been shown to increase emissions of the potent GHG nitrous oxide (N2O). Here we test whether these earthworm-induced N2O emissions also occur in the field. We quantified N2O emissions in managed grassland in two different seasons (spring and autumn), applying two different types of fertilizer (organic and artificial fertilizer) and under two earthworm densities (175 individuals and 350 individuals m(-2)) of the species Lumbricus rubellus (Hoffmeister). We found an increase in earthworm-induced N2O emissions of 286 and 394% in autumn for low and high earthworm densities (P = 0.044 and P = 0.007, respectively). There were no effects of earthworms on N2O emissions in spring. Fertilizer additions significantly increased cumulative N2O emissions and grass N content in spring and autumn. For grass N content interactions between earthworm addition and fertilizer type existed in both seasons. Our results suggest that the pathways through which earthworms affect N cycling (and thereby N2O emission) differ with weather conditions. We postulate that in spring the dry weather conditions overruled any earthworm effects, whereas in autumn earthworms mainly improved soil aeration and thereby increased both plant N uptake and diffusion of N2O to the atmosphere. While we showed the presence of earthworm-induced N2O emissions in managed grassland under field conditions for the first time, the nature and intensity of the earthworm effect in the field is conditional on soil physicochemical parameters and thereby on meteorological and seasonal dynamics. (C) 2013 Elsevier B.V. All rights reserved.
Amazing grazing : All weather beweiding
Lubbers, I.M. - \ 2013
aardwormen - broeikasgassen - bodembiologie - emissie - universitair onderzoek - earthworms - greenhouse gases - soil biology - emission - university research
egenwormen blijken een flink aandeel te hebben in de opwarming van de aarde. Dat blijkt uit een onderzoek dat de Wageningen Universiteit samen met internationale collega's uitvoerde. Regenwormen, bekend van hun vermogen de bodemvruchtbaarheid te verbeteren, blijken de uitstoot van broeikasgassen vanuit de bodem flink te verhogen; koolzuurgas gemiddeld met 33% en die van lachgas met 42%. Lachgas kan gemakkelijker via hun gangenstelsels ontsnappen naar de atmosfeer voordat het omgezet kan worden naar het onschadelijke stikstofgas.
Greenhouse-gas emissions from soils increased by earthworms
Lubbers, I.M. ; Groenigen, K.J. van; Fonte, S.J. ; Six, J. ; Brussaard, L. ; Groenigen, J.W. van - \ 2013
Nature Climate Change 3 (2013). - ISSN 1758-678X - p. 187 - 194.
nitrous-oxide fluxes - organic-matter dynamics - carbon-dioxide - ecosystem engineers - agricultural intensification - nitrifier denitrification - endogeic earthworms - microbial activity - n2o emission - crop residue
Earthworms play an essential part in determining the greenhouse-gas balance of soils worldwide, and their influence is expected to grow over the next decades. They are thought to stimulate carbon sequestration in soil aggregates, but also to increase emissions of the main greenhouse gases carbon dioxide and nitrous oxide. Hence, it remains highly controversial whether earthworms predominantly affect soils to act as a net source or sink of greenhouse gases. Here, we provide a quantitative review of the overall effect of earthworms on the soil greenhouse-gas balance. Our results suggest that although earthworms are largely beneficial to soil fertility, they increase net soil greenhouse-gas emissions
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