Projecten - prof.dr.ir. JW (Jan-Willem) van Groenigen

PhD project of Erne Blondeau: "Groundwater level effects on peat oxidation in Dutch pastures on peat soils"

Peat soils play an important role in the global carbon cycle, through their ability to sequester large stocks of carbon. However, drainage of peat soils enhances organic matter oxidation, leading to emissions of CO2 and N2O, and soil subsidence. In the Netherlands, many of the peat soils are drained for use as grassland for dairy farming. The Dutch government aims to reduce the annual greenhouse gas emissions from peat soils with one Mton CO2-eq by 2030. Therefore they have expressed their intention to raise the groundwater level in peat meadows towards 40 to 20 cm below the surface. While rewetting of peatlands reduces CO2 emissions, it can result in a trade-off with emissions of N2O or even CH4. In my research project, I study the underlying processes behind peat oxidation and the effects of management strategies on greenhouse gas emissions from peat meadows. The project involves experiments on the lab and field scales, studying the effects of groundwater level, soil moisture content, fertilizer application and cattle grazing on greenhouse gas emissions from peat soils. This PhD project is part of the NWO research program on land subsidence in the Netherlands, Living on Soft Soils (LOSS).

More information: Erne Blondeau

PhD project of Tullia Calogiuri: “The role of earthworms in enhanced mineral weathering: understanding their impact on carbon dynamics and sustainable fertilisation”

Carbon Dioxide Removal (CDR) technologies are required to reduce atmospheric carbon dioxide (CO2) concentrations and meet the goals of the 2015 Paris Agreement for climate stabilisation. Enhanced Rock Weathering (ERW) is a CDR with a great potential for CO2 capture, which could significantly contribute to mitigation goals in the next decades. Previous studies have mainly focused on the abiotic factors governing this process, such as rock type and grain size. The role of soil biota, specifically of earthworms, has been largely understudied in the context of ERW. Few studies have hypothesised a series of mechanisms through which earthworms could enhance weathering, but until now no research has focused on how to optimise the power that earthworms can have on ERW and how this can have a beneficial effect on climate change mitigation and carbon sequestration. Within this context, this project (part of the BAM! European project Home - FET-BAM) aims at accelerating the rates at which carbon can be sequestered by rock weathering through the action of earthworms, and understanding the underlaying mechanisms of these processes. This is tested through a series of rounds of two-months experiments in a climate chamber by using a unique set-up and combining different earthworm species and individuals rock powders and relative grain sizes, organic materials, and water flow rates and frequencies. This way, we can investigate which factors lead to better living conditions for earthworms and how earthworms affect weathering indicators and carbon sequestration. Secondly, using an organo-mineral system with a double labelled plant residue, we trace how earthworms influence the formation and distribution of organic and inorganic carbon through ERW. Additionally, due to the potential of mineral weathering to concurrently contribute to soil fertilisation, this project aims at using the organo-rock mixture processed by earthworms as a fertiliser to ultimately contribute to sustainable fertilisation and carbon sequestration. This will be tested through a pot experiment in the greenhouse with two different plant species and soil types. The overall main goal of this project is to provide a mechanistic understanding of earthworms' impact on mineral weathering and carbon dynamics and a new product for sustainable soil fertilisation. 

More information: Tullia Calogiuri

PhD project of Zhongchen Yang: "Impacts of antibiotic residues in manure on soil nitrogen cycling"

Circular agriculture aims to close elemental cycles which increases reliance on animal manure as soil fertilizer. However, veterinary antibiotics are still commonly used in animal husbandry to treat bacterial infections, leading to large amounts of antibiotics being excreted in manure. After applying manure containing antibiotics to soils, the fate and effects of these residues in soil have raised concerns regarding microbial antibiotic resistance and, more recently, nutrient cycling. Recent studies show that antibiotics in soil can potentially impair soil microorganisms and the physiology of plants. Since soil microorganisms and plants play crucial roles in soil nutrient cycling, the impacts of antibiotics on soil nutrient cycles, especially soil nitrogen (N) cycling, deserve further investigation.

To address this, two incubation experiments were conducted: one to test the impacts of different antibiotics in the same soil and another to examine the effects of the same antibiotic in different soils. Additionally, the impacts of antibiotics on plant-soil interactions are not well understood. To fill this research gap, a greenhouse experiment was carried out. We investigated how antibiotics alter plant-microbe interactions of grassland species, soil N2O emissions, N fixation, and N mineralization. The results will support policy development for a circular agro-economy by identifying hidden risks of antibiotic residues in manure applied to soil.

More information: Zhongchen Yang

PhD project of Jurrian van Waaij: “NOx emissions from agricultural soils”

N fertilization is applied to soils to increase crop production, but also comes with the cost of N losses to the environment. These N losses lead to eutrophication, biodiversity losses and other detrimental outcomes. Therefore, these N losses must be mitigated. One of these loss pathways is NOx emission, but this has not yet received much scientific attention, leading to uncertainty about viable mitigation strategies. My PhD project aims 1) to assess the magnitude of NOx emissions from agricultural soils and relate them to soil properties; 2) to explore the effects of soil temperature increases and drying-rewetting events on NOx emissions; and 3) to explore possible mitigation strategies through adapted agricultural practices which minimize pollution swapping, i.e., lowering NOx emissions at the cost of increasing other emissions.

More information: Jurrian van Waaij

PhD project of Dorien Westerik: "Mitigation options for nitrous oxide emissions in temperate and tropical agroecosystems”

Nitrous oxide is one of the main greenhouse gases (GHG) emitted from agroecosystems, mainly originating from nitrogen (N) transformations in soil after organic and mineral fertilizer application. Despite decades of research, it is only partially clear what the most promising mitigation options for N2O emissions are, and there is a particular lack of studies focused on tropical agroecosystems. The main goal of this PhD project is to investigate potential management options for mitigation of (yield-scaled) nitrous oxide emissions in temperate and tropical agroecosystems. To do so, I will perform a series of field and incubation experiments in temperate (Dutch) and tropical (Zambian) agricultural soils. These experiments will provide insight into whether the most effective mitigation measures are generally applicable, or whether they should be specific for different climatic zones and agroecosystems.

In Zambia, I focus on an intensively managed coffee system and compare different management practices such as fertilizer source and -rate. The experiments will contribute to the scarce amount of empirical data of nitrous oxide emissions from African soils. This research is part of the Ground Zero project, which aims to provide a framework of indicators and methods for the assessment of the carbon footprint, soil health and biodiversity in cocoa and coffee production systems.

In the Netherlands, I focus on intensively managed grassland systems and compare different species (mixtures) and fertilizer rates. Adjusting grassland species can mitigate N2O emissions through increased N uptake, biological nitrification inhibition and biological N fixation. This research is part of a public-private funded project which assesses different nitrous oxide mitigation options for grassland systems.

In addtion to the field studies in both countries, a series of (parallel) incubation studies with soils from both sites will be performed to study the behaviour and dominant pathways of nitrous oxide production in response to different pH levels and N sources and whether they differ between tropical and temperate soils.

More information: Dorien Westerik

PhD project of Gonzalo Pacheco Aguilar: “Climate resilience of soil carbon cycling in agroforestry systems”

Climate change is intensifying the hydrological cycle – which will alter, and possibly transform, croplands. Agroforestry is widely proposed as a management practice suited to buffer the impact of extreme weather events on agricultural soil carbon cycling. However, our understanding of soil response to drought is inconclusive, as is the role of trees in it. One of the main challenges is that the fate of soil carbon is entangled in complex interactions between plants and soil microbes, whose activity is tightly linked to moisture fluctuation. In this project, we aim to deepen our knowledge about the effect of tree-driven microclimatic conditions on the joint response of plants and microbes to drought, and the resulting consequence for soil carbon cycling. To this end, a series of laboratory and greenhouse experiments will be conducted with a focus on net ecosystem exchange and soil organic matter formation under extreme moisture fluctuation.

More information: Gonzalo Pacheco Aguilar

PhD project of Enno Sonntag: "Earthworm Farming as a Sustainable Protein Source in Circular Food Systems "

Earthworms play a key role in organic matter decomposition and nutrient cycling. Farming of litter-dwelling (epigeic) earthworms on organic residual streams, also known as vermiculture, produces vermicompost, a high-quality organic amendment. However, it also produces earthworm biomass. Earthworms are rich in protein and are traditionally used as a food source by various cultures around the world. In the search for new healthy and sustainable food sources, farmed earthworms have been proposed as an alternative protein source for food applications, with the added potential of improving food system circularity. However, important questions regarding vermiculture as a source of edible protein in circular food systems are currently unanswered. This PhD-project therefore seeks to quantify the nutritional composition of earthworms, optimize the productivity of vermiculture using spent mushroom substrate as feed, and assess impacts of vermicompost application on soil organic matter dynamics in a highly weathered soil. This research is part of the LandLessFood project and a cooperation between the Thünen Institute of Organic Farming (Germany) and the Soil Biology and Farming Systems Ecology research groups at Wageningen University.

More info: Enno Sonntag

PhD project of Jordy van ‘t Hull: "Trade-offs between carbon sequestration and nitrous oxide in Dutch Agricultural soils"

In line with the Paris Agreement of 2015 and the subsequent National Climate Agreement in 2019, the Dutch government aims to reduce greenhouse gas emissions from the agricultural and land-use sector with an additional 3.5 Mt CO2-eq by 2030. This includes a reduction in emission of  1 Mt CO2-eq for peat meadow areas, as well as sequestration of  0.5 Mt CO2-eq year-1 in agricultural land (mineral soils) in the Netherlands. However, the potential measures in the Climate Agreement are focused on the Carbon (C) balance (CO2 emissions versus carbon sequestration), whereas possible trade-offs with (enhanced) emission of nitrous oxide (N2O) is not considered. It is known that such trade-off effects exists, but it remains unclear how large these effects are and what the net effect is on the total greenhouse gas (GHG) balance. There is a need to quantify the effects of carbon measures on N2O emission in order to implement effective measures to meet the goals that are set by the Dutch Government. There are three potential measures that Dutch farmers can implement to sequester C and are important for N2O- emission. The measures to be considered are: Water Infiltration Systems (WIS) and Pump Regulated Infiltration Systems (PRIS) on peatland; adding organic fertilizers to mineral soils; and grassland management (time and method of grassland cultivation). Thus, the objective of this project is to identify and quantify the potential trade-off of these measures on N2O emission. In addition, the proposed measures cause changes in the soil carbon stock. Therefore, more insight in the effect of a higher soil organic matter content (SOM) is required to determine the possible N2O trade-off in relation to carbon sequestration.

More information: Jordy van 't Hull

PhD project of Ángel Velasco Sánchez: " The role of soil microorganisms in enhancing phosphorus availability from dairy processing waste in grasslands "

Dairy industry is one of the largest agri-food industries across the world. The production of dairy products results in the production of large amounts of wastewater with a high phosphorus (P) content. Considering the current environmental threats and limited availability of P sources, wastewater from dairy industry may be an important circular source of P for agriculture. To better understand and to investigate new technologies to recover and apply P materials as fertilizers, the H2020 REFLOW (Phosphorus Recovery for FertiLisers from dairy processing Waste) project was funded by the European Commission. REFLOW investigated, through a network of thirteen early stage researchers, the recovery and production of P-rich fertilizers from dairy processing wastewater, the evaluation of their agronomic and environmental impacts and their economic assessment and potential.

My work within the REFLOW project involved the study of the agronomic potential of P recycled fertilizers. Particularly, I was focused on the availability of P for crops from such recycled materials and how this can be enhanced by the activities of soil microorganisms. To this end, I investigated the different chemical forms of P present in dairy processing waste through P fractionation schemes, conducted soil incubation experiments to understand the dynamics of P availability as affected by the activities of soil microorganisms. Lastly, I have also conducted greenhouse and field experiments to understand the interactions between roots and soil microorganisms to increase the availability of P from dairy processing materials.

More information: Ángel Velasco Sánchez