Functional diversity

In the Functional diversity theme we apply evolutionary game theory (e.g. tragedy of commons, kin selection) and ecological theory to better the mechanisms that drive interactions among crop plants and interactions with other organisms (e.g., weeds, pests and pathogens) within crop ecosystems. We use this knowledge to explore opportunities for ecological intensification of agriculture by exploiting spatial and temporal diversity, e.g., by mixed species cropping (intercropping, agroforestry), crop rotation and variety mixtures.

Thesis subjects

Quantifying plant traits that contribute to weed suppression in a cereal-legume intercrop

Description: 

Intercropping is the agricultural practice where two or more crop species are cultivated simultaneously within a single season on the same area of land. One of the potential benefits of intercropping is improved weed suppression compared to the average of the monocrops. In a cereal-legume intercrop system, the cereal component crop contributes more to weed suppression than expected from the sole crop stand, which causes this benefit. Through a combination of field experiments and simulation modelling, plant and crop traits that are responsible for this phenomenon can be identified and quantified.

Functional-structural plant (FSP) modelling is an advanced modelling technique that can dynamically simulate plant structures in interaction with the environment to simulate 3D plant growth in space and time. Such a model can accurately capture detailed processes in how plants react to other plants and their environment. Currently, our modelling of plant plasticity in response to its environment needs further development. Understanding the mechanisms responsible for the difference in weed suppressiveness between intercrops and monocrops and the proper implementation in our current FSP model is needed. This will make it possible to identify and quantify plant traits that constitute a good intercrop component crop in terms of weed suppression.

Objectives and methods:

The aim of this project is to identify and quantify the plant and crop traits responsible for enhanced weed suppression in intercrops. A field experiment will be done to gather data. This data is used to develop and parameterise an FSP model. Data from both the field experiment and FSP model simulations is used for the final analysis. Within this topic it is possible for the student to develop their own research ideas.

Required skills:

Basic statistics. Useful but not required: maximum likelihood estimation, R, Java, FSP modelling, field work experience.

Types of research:

Field experiment (different cereal-legume intercropping systems and their sole crop stands); FSP modelling (developing plant plasticity responses; simulations of cereal-legume intercrop systems); data analysis.

Contact:

For further information on this thesis subject, please contact us.

David Kottelenberg (david.kottelenberg@wur.nl), Lammert Bastiaans (lammert.bastiaans@wur.nl), Jochem Evers (jochem.evers@wur.nl)

Quantifying the effect of intercrop design on weed suppression and crop yield

Description:

Intercropping is the agricultural practice where two or more crop species are cultivated simultaneously within a single season on the same area of land. One of the benefits of intercropping better weed suppression than expected from the monocrop averages. This phenomenon is attributable to plastic responses of the plants to neighbouring plants. To make optimal use of this phenomenon for intercrop productivity, a better understanding of the influence of different intercrop system design variables, such as population density and sowing pattern, is needed.

Objectives and methods:

The aim of this project is to quantify the influence of different system design strategies (e.g. plant density, component crop ratio, within-row mixing) on weed biomass and crop yield. A field experiment will be done to gather data on different design strategies. Optionally, a functional-structural plant (FSP) model can be applied and calibrated to gather data from simulations in which additional designs can be investigated in silico. Within this topic it is possible for the student to develop their own research ideas.

Required skills:

Basic statistics. Useful but not required: maximum likelihood estimation, R, field work experience, FSP modelling.

Types of research:

Field experiment (different cereal-legume intercropping systems and their sole crop stands); FSP modelling (simulations of cereal-legume intercrop systems); data analysis.

Contact:

For further information on this thesis subject, please contact us.

David Kottelenberg (david.kottelenberg@wur.nl), Lammert Bastiaans (lammert.bastiaans@wur.nl), Jochem Evers (jochem.evers@wur.nl)

Forage quality in intercropping

Description: 

Intercropping is an ancient practice that has been marginalized by modern intensive agriculture. However, intercropping may be a means to solve some of the major problems associated with modern agriculture, thereby contributing to the realization of productive, effective, and sustainable agriculture. Intercropping has been found to significantly increase the yield, resource use efficiency, and agriculture ecosystem services. However, there are also many intercropping systems that are not aiming to harvest grains but to produce forage. Thus, the forage quality of intercropping should be determined. Two years of perennials (red clover, whiter clover and lucerne) maize intercropping field trials will be conducted in Wageningen, the Netherlands. Parameters related to plant development and growth, yield and forage quality, nitrogen uptake and use efficiency, soil microbial community composition, greenhouse gases emission, leaf area index and radiation use efficiency in different planting patterns will be analyzed.

This study aims to investigate the forage yield, forage quality and greenhouse gases emission in maize perennial legume intercropping system. This study improves our understanding of the forage quality of intercropping system aims for forage production.

Type of research:

We offer the opportunity for interested students to take part in an experiment of a PhD project on maize perennial intercropping system. The perennials have been sown in late August 2021. The greenhouse gases will be measured in conjunction with Meteorology and Air Quality group. The forage quality measurement and ensiling experiment will be carried out in Animal Nutrition group. The rest measurements field works, and lab works will be conducted in the Unifarm. Please have a look at which section you are interested in and which section you would like to participate in.

Field work in Wageningen

Laboratory work in (Unifarm/ANU/MAQ)

Experimental data analysis

Contact:

If you are interested, please contact us.

Hao Liu (hao1.liu@wur.nl), Prof. Dr. Paul Struik (paul.struik@wur.nl)

Can R/FR signaling in an intercropping system regulate root system development?

Description: 

The canopies of intercropping systems typically consist of crop species of different heights. This heterogeneous distribution of the canopy results in patterns of light capture (photosynthetically active radiation, PAR) and light signaling (red to far-red ratio, R:FR) different to sole crops, which are much more uniform. R/FR ratio is used by plants as an indicator of plant proximity. Low R/FR ratio induces plastic responses in shoot and root system development. Even though we know a lot about aboveground responses to shading signals, how plant use this light signal received by photoreceptors to regulate their development belowground, and what this means for plant performance, is rarely studied. There are indications that root system development is stimulated at a low R/FR ratio, but it is unclear to which extent this could play a role in the plant-plant interactions in intercropping systems. This shoot to root communication might help plants coordinate resource partitioning under interspecific competition in intercropping systems, and therefore play an important part in determining intercrop performance benefits.

This study aims to understand if the difference of light conditions in the mixed stand (intercropping) and mono stand (sole crop) will trigger altered root system development. The research on interactions between above- and belowground plant–plant signaling is will improve our understanding of the mechanisms of interactions in intercropping.

Types of work:

We offer the interested MSc student the opportunity to participate in an experiment in the context of a PhD project on intercropping. The wheat/faba bean mixtures will be grown in the greenhouse at Unifarm under altered light conditions. Shoot and root traits will be observed during the vegetative period. Roots will be scanned and analyzed to quantify root architecture and morphology.

Location:

Wageningen  (WUR Crop Systems Analysis)

Starting date:

February 2022, for a period of 6 months (specific dates can be negotiated)

Contact:

Jin Wang (jin.wang@wur.nl), Jochem Evers (jochem.evers@wur.nl), Hannah Schneider (hannah.schneider@wur.nl)

Behavioural responses of insect herbivores to shading cues

Description: 

Plants use many cues to get the latest news on their environment, from volatiles released by insect-infested neighbouring plants to light signals from different parts of the spectrum. An important cue for plants to detect competitors and future shading is the ratio between red light (absorbed by foliage) and far-red light (reflected by foliage). In response to a low red to far-red (R:FR) ratio, plants elongate stems and petioles and change leaf angles to keep up with their neighbours. In addition, a low R:FR ratio affects defence levels by repressing the activity of the jasmonate pathway. As a consequence of R:FR mediated defence, insect herbivores feeding on plants exposed to low R:FR perform better. However, recent experimental results in which caterpillars were feeding on low R:FR exposed plants show that these effects are species dependent. Moreover, results of a pilot experiment where caterpillars were fed on an artificial food source, suggest that R:FR can have a direct effect on the growth rate of caterpillars.

In this thesis project you will further explore to what extent herbivores can directly respond to R:FR cues. This will be done by studying herbivore behaviour under contrasting levels of R:FR through various means. For example, one could look at feeding preference or feeding activity under various R:FR regimes. We are looking for a creative, motivated student with good experimental skills. We offer a challenging thesis supervised by enthusiastic supervisors.

Contact:

Bob Douma (Centre for Crop Systems Analysis, Bob.Douma@wur.nl), Marcel Dicke (Laboratory of Entomology, Marcel.Dicke@wur.nl), Davy Meijer (Laboratory of Entomology, Davy.Meijer@wur.nl

Yield potential and resource use efficiency in intercropping

Description: 

Intensive agriculture is an effective pathway to meet the increasing demand for food, feed and fuel in our limited arable land. Intercropping has been proved having higher productivity, better agriculture ecosystem services than monoculture at field level. Regional assessment of the role of intercropping in food security is needed, thus the potential yield of intercropping should be determined and tools need to be developed to assess it under varying conditions. Two years of wheat maize intercropping field trials have been conducted in Wageningen, the Netherlands. The characteristics of plant development and growth, yield and its components, radiation use efficiency, maize photosynthesis rate during flowering period, nitrogen uptake and use efficiency in different planting configurations are going to be analysed. An intercropping model will be parameterized to explore the yield potential for varying planting configurations and growing conditions.

Types of research: 

Laboratory work in Unifarm, experimental data analysis, crop modelling

Location: 

Wageningen

Contact:

For details on potential thesis subjects contact Wopke van der Werf (wopke.vanderwerf@wur.nl)

Pushing and pulling: how pyrethrum can both attract and deter insects

Description:

Pyrethrum Tanacetum cinerariifolium and some other species in the genus Tanacetum are perennial species that produce pyrethrins that are used as natural pesticides, especially in organic agriculture. The ecological significance of pyrethrin production is known to be both protection of the plant against insects and, as pyrethrin accumulate in flowers and seeds, protection of offspring against fungal attacks. However, Pyrethrum is also insect pollinated probably primarily by thrips and like other flowering plants the flower is designed to attract pollinators. Pollination is known to be poor in general, however. Thus, an interesting combination arises, as flowers are both made to attract pollinators and at the same are loaded with pyrethrins that deter insects. It has been hypothesized that this represents a so-called push-pull strategy by the plant, in which an ecological balance between sufficient reproduction and annual survival is reached. Roughly this idea entails that these flowers are cleverly designed to attract sufficient pollinators but simultaneously deter potential herbivores so that reproductive success is not diminished. Understanding this dynamic is ecologically highly relevant as it leads to better understanding of why flowers are designed the way they are, but is of major agricultural importance as well, because pollination is also correlated to pyrethrin content and therefore economically important.

Project:

An experiment was conducted in which different Pyrethrum accessions with unknown variation in Pyrethrin content were grown and were either exposed to thrips or not. Flowers were collected both at the pollination stage (stored in alcohol) and at the ripe stage for seed experiments. The question to be addressed here is if there is correlation between pyrethrin content and the number of thrips on the flowers and also whether there is a relation between the presence of thrips and pollination success. Experiments will be conducted (i) to see whether the presence of thrips has influenced the number of fertile seeds, and (ii) whether the pyrethrin content has affected the thrips numbers. In addition we have a suite of accessions from a wild sister species with a known variation in pyrethrin contents and some distinct differences with pyrethrum. These are growing in a field plot and can be characterized in various ways. Several types of measurements or small experiments are possible. 

The project is supvervised by Niels Anten (CSA) en Maarten Jongsma (PRI)

Location:

Wageningen

Contact:

Niels Anten (niels.anten@wur.nl)

Ecological weed management: controlling weeds without herbicides

Description:

Weeds are a serious biotic production constraint in most agricultural production systems. Acting at the same trophic level as the crop, weeds capture resources that cannot anymore be used by the crop. Therefore, leaving weeds uncontrolled will sooner or later lead to considerable reductions in crop yield.

Curative weed control is mainly focussed on weed seedlings and is strongly dominated by the use of herbicides. This heavy reliance on chemical control is considered objectionable because of potential negative side-effects on food safety, public health and the environment. Additionally, cropping systems with a narrow focus on herbicidal control are  less sustainable, due to an increased risk regarding the development of herbicide resistance.

Cultural control refers to any adjustment of the general management of the crop that contributes to the regulation of weed populations and reduces the negative impact of weeds on crop production. This preventative approach addresses a variety of life cycle stages and relevant processes, like the weed soil seed bank, seed recruitment, weed seed production and seed predation. Various measures like photo-control, bio-fumigation, mulching, stale seedbeds, transplanting, weed suppressive cultivars and no till systems potentially contribute to this kind of ecological weed management.

The questions that remain are manifold, just to mention a few:

  • Which life cycle stage of the weeds can best be tackled?
  • How effective and reliable are individual cultural control measures?
  • Do the measures combined provide synergistic effects?
  • Are weed community changes likely to result from a modified management strategy?
  • What is the role of crop rotation in ecological weed management?

Types of research:

  • Literature review with follow up analyses of already published data
  • Experimental approaches to evaluate individual measures
  • Population dynamical models to evaluate control measures and to study changes in weed community composition.

Location:

Wageningen

Contact:

Lammert Bastiaans (lammert.bastiaans@wur.nl)

Sustainable control of blackgrass in cereal production systems in the Netherlands

Description:

Herbicidal resistance against blackgrass (Alopecurus myosuroides) is frequently reported in regions with continuous cropping of winter cereals. In the Netherlands, the problem is steadily increasing in ‘de Oldambt’ in North-east Groningen. This area is characterized by heavy clay soils, making the production of root crops virtually impossible, whereas the gross margin of many mown crops is simply too low to be an attractive alternative. Consequently, continuous cropping of winter cereals is common practice. The low number of herbicides available for managing weeds in these crops results in repeated use of just a few compounds; an ideal environment for the development of herbicide resistance. Problems with blackgrass have steadily increased in recent years. Integrated weed management strategies, including cultural control measures and crop rotation, are needed to lessen the problem. In this study, the ecological and biological properties of the weed will be investigated and options to undermine the success of the species will be identified. A weed population model will be developed to quantitatively estimate the effectivity of the proposed measures in the long run. Parameterization of the blackgrass model will be based on literature search, expert opinion and experimentation.

Contact:

Lammert Bastiaans (lammert.bastiaans@wur.nl)

Meta-analysis of the role of planting density on pest prevalence and disease incidence

Description

Plant density is a key factor in regulating pest and disease epidemics. According to the resource concentration hypothesis plant density will positively affect density of insects and pathogens. With increasing planting density, microclimate alters, movement between plants becomes easier and plant defenses may be lowered because of increased investment in competition. A qualitative scoring of papers publishing the effects of plant density on the abundance of phytophagous insects showed a positive affect of plant density on host abundance in only ~34% of the studies (Rhainds & English-Loeb, 2003). Others reported as positive effect in ~57% of the studies. As the effect of plant density on pest abundance can be both positive and negative, a better understanding is needed to what determines the relationship between host density and pest abundance. A better understanding on the relative contribution of factors that contribute to disease epidemics as a function of host density is crucial in both managed and natural ecosystems.

Type of work

In this thesis project you will do a quantitative review of the literature (meta-analysis) to investigate the overall relationship between plant density and disease prevalence, and to try uncover factors that affect this relationship. This involves a lot of reading, data, statistics and fun.

I am looking for a motivated student that is interested in this relevant topic, and likes to do a theoretical study using literature and statistics.

Contact

Bob Douma (bob.douma@wur.nl, 0317-482140)

The potential of pest and disease suppression in an intercrop system

Description:

Pesticides and fungicides are often the farmer’s main means of crop protection. However, with more restriction being put in place on the use of these products, and the development of fungicide-resistance among pathogens, alternative protection measures need to be explored. Intercropping has many benefits, among one is the potential to reduce pests and diseases, and could thus be a alternative disease management practice. This MSc thesis project will focus on the potential of a potato-based intercrop system for pest and/or disease suppression. We will explore how intercropping affects different stages of the epidemiology, and which mechanisms play a role in disease suppression. Students can participate in a planned field experiment to monitor various aspects of pest and/or disease in potato.

In this project you will explore the potential of intercropping potato for pest/disease control. The current aim of the project is to focus on Phytophthora infestans, but we are open to include other diseases or pests (e.g. Colorado potato beetle, aphids, Alternaria), depending on your interest. Different aspects of the disease can be measured, for example incoming spores, disease progress or disease severity. Aspect of the canopy with reference to disease can be measured, such as microclimate, or the morphological or physiological characteristics of the potato plants.

Starting date:

April/May 2021

Contact:

If you have questions do not hesitate to contact us: Zohralyn Homulle (zohralyn.homulle@wur.nl) and/or Bob Douma (bob.douma@wur.nl, 0317-482140).