Functional biodiversity in crop-crop and crop-weed interactions

This theme explores the mechanisms that drive plant-plant (e.g. crop-crop, crop-weed) interactions as well as interactions between plants and other organisms within crop ecosystems, and how these interactions scale to crop-level aspects, such as yield, resource-use efficiency, crop interactions with insects and other non-plant organisms and climate feedbacks. Particular emphasis is placed on the role of intraspecific and interspecific interactions. The ecology and non-chemical control of weeds is a focal area of interest. In this way CSA studies crops ranging in both spatial and temporal diversity (e.g. intercropping, different rotation systems, multi-variety crops) as well as semi natural systems (e.g. agro forestry, non-timber forest products).

Thesis subjects

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)

Clever Cover Cropping: Cover Crop Diversity and Productivity

Description:

Cover cropping is a classical agricultural practice that contributes to the buildup of soil organic matter (SOM), which in turn allows for ecological intensification. Cover cropping contributes to various ecosystem services, including nutrient cycling and C-accumulation, reduction of soil erosion, soil quality improvement, enhancement of soil biota, weed suppression, water management and enhancement of  the productivity of the main crop.

Globally, cover crops (CC) are mainly grown in pure stands. However, many studies in natural grasslands and intercropping of food crops have shown the advantages of mixed plant species. In line with this, we hypothesize that ecosystem services provided through cover cropping, build up SOM in particular, can be maximized by mixing CC species.

In a new research project, our objective is to investigate whether CC mixtures outperform pure stands. If this is observed, we will try to identify the mechanisms that are responsible for shaping the performance of a CC mixture. Apart from species selection, other factors might influence the performance of CC mixtures. In this new project particular attention will be given to the optimal number of species to be included in a mixture and the spatial arrangement of the component species.

Type of research:

There are four proposed MSc topics:

1. Species comparisons for different CC species grown in pure stands, e.g., screening for plant emergence, early development, morphology, robustness, nutrient uptake, and biomass production. The experiment will be conducted in an open field located in Wageningen and at the stakeholders (breeding companies) sites.

2. Study on the influence of spatial arrangements and row spacing on mixture performance. In this field experiment several binary mixtures of CC species will be intercropped in two different designs, mixing within the row and between rows (alternate rows). FSPM and other modelling programs can be used to study plant plasticity (optional).

3. The effect of increasing the number of component species within a mixture on nutrient uptake, productivity and resilience. In this experiment several combinations of CC species will be created e.g, pure stands, 2-species mixtures, 4 species mixture and 8 species mixtures.

4. Meta-analysis on the productivity and resilience of cover crop mixtures.

Used skills:

Field work, design experiments and statistical analysis.

Requirements:

Good knowledge of crop growth and statistical analysis (FSPM and Meta-analysis is optional). Driving licence is preferable

Location:

Wageningen

Contact:

Ali Elhakeem (ali.elhakeem@wur.nl), Lammert Bastiaans (lammert.bastiaans@wur.nl)

Modelling crop-weed interactions in 3D

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. A sustainable way to suppress weed growth in a crop canopy is by improving crop competitiveness. This can be achieved by changing architectural traits of the crop plants that enhance its competitive strength, such as early soil cover, as well as optimized leaf orientation and branching patterns. Crop competitiveness can also be improved by changing population characteristics such as crop population density, presence of secondary competitive crops or the uniformity of crop plant arrangement. In all cases, the balance between competition with weed plants (interspecific competition) and competition among crop plants (intraspecific competition) will determine whether the increased crop competitiveness will result in improved weed suppression.

Experimental and modelling work conducted in recent years has shown that substantial gain in crop competitiveness is to be expected by combined optimization of plant and canopies characteristics. The focus of this thesis work is to explore the balance between inter- and intraspecific competition for light in crop-weed canopies, in relation to plant and canopy characteristics. Potential questions to be addressed are: how does canopy uniformity relate to weed suppression? Which crop traits make a crop more competitive with weeds and how does this depend on population density? What is the influence of the moment of weed emergence in this? Which crop plant architecture is optimal for weed suppression? To address such questions, a 3D functional-structural plant (FSP) model of crop-weed interactions is available that simulates growth and development of individual crop and weed plants in a specific arrangement.

Types of work

This work is a modelling study. There is flexibility in which questions will be explored using the FSP model, but it will be limited to competition for light. The model available can be used as it is, requiring only parameter value adjustments, or it can be adapted and modified to accommodate simulation of processes it is currently lacking – this is up to the student’s learning goals. The topic is suitable for students who are interested in plant-plant interactions and ecological weed control, but also for those who wish to develop FSP modelling skills.

Location

Wageningen (WUR Crop Systems Analysis)

Contact

Jochem Evers (jochem.evers@wur.nl), Lammert Bastiaans (lammert.bastiaans@wur.nl)