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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    Bee abundance and soil nitrogen availability interactively modulate apple quality and quantity in intensive agricultural landscapes of China
    Wu, Panlong ; Tscharntke, Teja ; Westphal, Catrin ; Wang, Meina ; Olhnuud, Aruhan ; Xu, Huanli ; Yu, Zhenrong ; Werf, Wopke van der; Liu, Yunhui - \ 2021
    Agriculture, Ecosystems and Environment 305 (2021). - ISSN 0167-8809
    Ecological intensification - Landscape composition - Pollinator - Robinia forests
    Bees provide important pollination services for crops, but pollination limitation is a common problem in agricultural landscapes worldwide. To promote ecological intensification in fruit production, more knowledge is needed concerning the interacting effects of insect pollination services and soil fertility on crop quality and quantity. We investigated the effects of three pollination treatments (open, self and hand pollination) on apple quantity and quality parameters. We also analyzed the effects of bee abundance (wild bees and managed honeybees (Apis mellifera)) and soil nitrogen on fruit quantity and quality, and the responses of bee abundance and species richness to landscape metrics. Apple fruit set and yield of open pollinated flowers increased by 57 % and 25 t/ha (compared to bagged controls), respectively. Hand pollination further enhanced yields by 7 t/ha (compared to open pollination; i.e. to 39 t/ha), indicating pollination limitation in the orchards. Seed number was highest in open pollinated fruits, and increased with bee abundance if soil nitrogen was low, but decreased with bee abundance at high nitrogen levels, possibly due to higher flower density resulting in pollinator dilution effects. Higher seed numbers reduced the proportion of deformed apples and thus increased fruit quality. The percent of surrounding semi-natural habitats positively affected species richness of wild bees in apple orchards. We conclude that yield and quality of apples may benefit from ecological intensification comprising the augmentation of wild bees by semi-natural habitat and lowering of fertilizer inputs.
    Kicking the Habit: What Makes and Breaks Farmers' Intentions to Reduce Pesticide Use?
    Bakker, L. ; Werf, W. van der; Sok, J. ; Bianchi, F.J.J.A. - \ 2020
    Ecological Economics 180 (2020). - ISSN 0921-8009
    Pest Management - Crop Protection - Barriers - Environmental Impact - Decision-Making - Intentions - Reasoned Action Approach
    There is a growing concern in society about the continuing intensive usage of pesticides in farming and its effects on environmental and human health. Insight in the intentions of farmers to reduce pesticide use may help identify pathways towards farming systems with reduced environmental impacts. We used the Reasoned Action Approach to identify which social-psychological constructs determine farmers' intentions to decrease pesticide use. We analysed 681 responses to an online survey to assess which constructs drive intention, and identified which beliefs pose barriers and drive the motivation of farmers to decrease pesticide use. Our results show that the intention to reduce pesticide use is strongly determined by whether other farmers also act. Furthermore, farmers perceive limited capacity and autonomy to reduce pesticide use, and motivations to reduce pesticide use were based on environmental considerations. Finally, decreasing pesticide use was considered risky, but the relative importance of risk attitude was offset by the environmental considerations of farmers. This indicates that farmers need successful examples of how to decrease pesticide use, either via exchange with peer farmers or knowledge provisioning on alternative pest control methods. These insights may be useful to direct policy making to influence farmers' intentions to decrease pesticide use.
    Neonicotinoids in global agriculture: evidence for a new pesticide treadmill?
    Bakker, L. ; Werf, W. van der; Tittonell, P.A. ; Wyckhuys, Kris A.G. ; Bianchi, F.J.J.A. - \ 2020
    Ecology and Society 25 (2020)3. - ISSN 1708-3087
    agrochemical pollution - Biodiversity loss - farmer decision making - Global change - insecticide dependency - Lock-in - neonicotinoids - pest management - pesticide treadmill - technological change
    Overreliance on synthetic insecticides in global agriculture is the outcome of a “pesticide treadmill,” in which insecticide-induced pest resistance development and the depletion of beneficial insect populations aggravate farmers’ pesticide dependencies. Examples of the pesticide treadmill have been witnessed repeatedly over the past seven decades, prompting the question whether the rapid uptake and usage patterns of neonicotinoid insecticides and their associated environmental impact are in accordance with this recurrent phenomenon. We hypothesize a conceptual framework in which treadmills are enforced by enabling or disabling drivers within four domains: pest management decisions at the farm level, characteristics of farming landscapes, science and technology, and societal demands. These drivers then tend to create a self-enforcing pesticide “lock-in.” We then analyze several post-1950s historical case studies with reference to this framework, e.g., those involving sprays of the highly hazardous DDT and methyl-parathion, in which the pesticide treadmill was initiated, sustained, and broken, and compare this with current patterns in neonicotinoid use. Historical case studies further illustrate how treadmills occur in three phases in which (i) a limited number of insecticides are routinely used, (ii) resistance development of pests results in the increased crop injury, prompting increased frequency of applications with a wider range of products, (iii) breaking out of the pesticide “lock-in” by policy change and adoption of alternative technologies that lowered chemical inputs and improved agro-ecosystem functioning. The analysis shows similarities as well as differences between neonicotinoid usage patterns and historic pesticide treadmills, and provides guidance on how to effectively avoid or dismantle pesticide treadmills in global agriculture.
    Phosphorus acquisition and yield gain in intercropping: empirical studies and meta-analyses
    Li, Chunjie - \ 2020
    Wageningen University. Promotor(en): E. Hoffland; Th.W. Kuyper, co-promotor(en): W. van der Werf; F.S. Zhang. - Wageningen : Wageningen University - ISBN 9789463954778 - 213
    Identification of species traits enhancing yield in wheat-faba bean intercropping: development and sensitivity analysis of a minimalist mixture model
    Berghuijs, H.N.C. ; Wang, Z. ; Stomph, T.J. ; Weih, M. ; Werf, W. Van der; Vico, G. - \ 2020
    Plant and Soil (2020). - ISSN 0032-079X
    Crop growth model - Faba bean - Intercrop - Mixture - Model - Sensitivity analysis - Strip intercrop - Wheat

    Aim: Cereal-legume intercropping can result in yield gains compared to monocrops. We aim to identify the combination of crop traits and management practices that confer a yield advantage in strip intercropping. Methods: We developed a novel, parameter-sparse process-based crop growth model (Minimalist Mixture Model, M3) that can simulate strip intercrops under well-watered but nitrogen limited growth conditions. It was calibrated and validated for spring wheat (Triticum aestivum) and spring faba bean (Vicia faba) grown as monocrops and intercrops, and used to identify the most suitable trait combinations in these intercrops via sensitivity analyses. Results: The land equivalent ratio of intercrops was greater than one over a wide range of nitrogen fertilizer levels, but transgressive overyielding, with total yield in the intercrop greater than that of either sole crop, was only obtained at intermediate nitrogen applications. We ranked the local sensitivities of the individual yields of wheat and faba bean of the whole intercrop under various nitrogen input levels to various crop traits. Conclusions: The total intercrop yield can be improved by selecting specific traits related to phenology of both species, as well as light use efficiency of faba bean and, under high nitrogen applications, of wheat. Changes in height-related crop traits affected individual yields of species in intercrops but not the total intercrop yield.

    Intercropping enables a sustainable intensification of agriculture
    Werf, Wopke van der; Li, Chunjie ; Cong, Wen Feng ; Zhang, Fusuo - \ 2020
    Frontiers of Agricultural Science and Engineering 7 (2020)3. - ISSN 2095-7505 - p. 254 - 256.
    Farm size and smallholders’ use of intercropping in Northwest China
    Hong, Yu ; Heerink, Nico ; Werf, Wopke van der - \ 2020
    Land Use Policy 99 (2020). - ISSN 0264-8377
    China - Farm size - Intercropping - Machinery - Risk

    Intercropping, i.e. the cultivation of crop species mixtures, can potentially reduce pressure on land resources by generating higher yields through exploitation of complementarities between crop species. Although intercropping is practiced on a non-negligible proportion of China's arable land, little is known about the factors that influence farmers’ decisions to use intercropping. In this study we develop a theoretical framework that distinguishes exogenous factors from endogenous factors in farmers’ activity choices in general and the use of intercropping in particular. We apply this framework in an empirical analysis of socio-economic factors affecting the use of traditional and novel relay intercropping systems, with a special focus on the impact of farm size, using primary data collected among 299 farmers in Gaotai County, northwest China. We find that large farms do no not plant more land with the traditional wheat/maize intercrop as compared to small farms, while land planted with the two novel intercrops is significantly larger on large farms. Availability of machinery has no negative effect on the area under intercropping, and has a significant positive effect on the use of one novel intercrop type. Our results confirm that risk considerations do not play a role in relay intercropping use decisions of Chinese farmers. We conclude that positive yield and natural resource effects of intercropping can still be realized if the ongoing farm scale enlargement policy is combined with a policy promoting novel intercropping types, particularly those types that can make use of already available machinery.

    Correction: Approaches to identify the value of seminatural habitats for conservation biological control
    Holland, John M. ; Jeanneret, Philippe ; Moonen, Anna Camilla ; Werf, Wopke Van Der; Rossing, Walter A.H. ; Antichi, Daniele ; Entling, Martin H. ; Giárd, Brice ; Helsen, Herman ; Szalai, Mark ; Rega, Carlo ; Gibert, Caroline ; Veromann, Eve - \ 2020
    Insects 11 (2020)5. - ISSN 2075-4450

    We would like to change the authors’ names and email addresses on page 195 of paper [1] from: John M. Holland 1,*, Philippe Jeanneret 2, Anna-Camilla Moonen 3, Wopke van der Werf 4, Walter A.H. Rossing 5, Daniele Antichi 6, Martin H. Entling 7, Brice Giffard 8, Herman Helsen 9, Mark Szalai 10, Carlo Rega 11, Caroline Gibert 12 and Eve Veromann 13 1 Farmland Ecology Unit, Game and Wildlife Conservation Trust, Fordingbridge SP6 1EF, UK 2 Agroecology and Environment, Agroscope, CH-8046 Zurich, Switzerland; philippe.jeanneret@agroscope.admin.ch 3 Scuola Superiore Sant’Anna, Agroecology Group, Institute of Life Sciences, Via Santa Cecilia 3, 56127 Pisa, Italy; moonen@sssup.it 4 Wageningen University & Research, Crop Systems Analysis, Droevendaalsesteeg 1, 6708PBWageningen, The Netherlands; wopke.vanderwerf@wur.nl.

    Removing top leaves increases yield and nutrient uptake in maize plants
    Raza, Muhammad Ali ; Werf, Wopke van der; Ahmed, Mukhtar ; Yang, Wenyu - \ 2020
    Nutrient Cycling in Agroecosystems 118 (2020)1. - ISSN 1385-1314 - p. 57 - 73.
    Maize - Nitrogen - Phosphorus - Potassium - Seed filling-phase

    Abstract: Intraspecific competition for light affects nutrient uptake of maize, especially during the seed filling phase (from the blistering-stage to physiological-maturity). Partial leaf removal only affects the top leaves and improves the light-environment, which could then enhance nutrient uptake during the seed filling phase. However, there is a shortage of quantitative information on the yield effects of such a management measure. A 3-year field trial was conducted to evaluate the impact of different leaf removal treatments (no removal of leaves (D0: control), removal of two leaves (D2), removal of four leaves (D4), and removal of six leaves (D6) from maize-canopy) on total dry matter accumulation, and nitrogen, phosphorus, and potassium uptake at the blistering-stage and physiological-maturity, plus seed number per plant, seed weight, and seed yield at physiological maturity. Compared to D0, at physiological-maturity, D2 significantly increased total dry matter accumulation (by 9%), and uptake of nitrogen (by 5%), phosphorus (by 10%), and potassium (by 4%); while excessive leaf removal treatments considerably reduced dry matter accumulation and nutrient uptake. Importantly, during the seed filling phase of maize, treatment D2 significantly enhanced the uptake of nitrogen, phosphorus, and potassium by 76%, 40%, and 65%, respectively, compared to control. Treatment D2 increased seed number per plant (by 6.4%, from 448 under D0 to 477 in D2) and seed weight (by 5.7%). Relative to control, maize in D2 had 12%, 14%, and 11%, higher seed-yields in 2017, 2018, and 2019, respectively, and it also improved the economic profit when taking into account labor costs. Graphic abstract: Graphical representation of changes in light transmittance, photosynthesis, nutrient uptake, carbohydrate, and dry matter accumulation in maize plants as affected by different leaf removal treatments. Treatment codes represent no defoliation (D0: control), removal of two leaves (D2), removal of four leaves (D4), and removal of six leaves (D6) from the top of maize canopy. Yellow and green arrows show the light environment and leaf area of maize plants. The black arrows represent the regulating directions of leaf removal treatments on maize growth and development in this paper. The graphical abstract clearly demonstrates the significant improvement of optimum leaf removal treatment (D2) as compared to control (D0). The red and blue arrows show the relevant increase and decrease of the mentioned components between the optimal leaf removal and control. [Figure not available: see fulltext.]

    Pilot Grasopname: ervaringen met het genereren en gebruiken van dagelijks kengetal grasopname in de praktijk : rapportage seizoen 2019
    Holshof, Gertjan ; Dixhoorn, Ingrid van; Philipsen, Bert ; Werf, Joop van der - \ 2020
    Wageningen : Wageningen Livestock Research (Wageningen Livestock Research rapport 1247) - 27
    Grass intake while grazing has been a large unknown factor in feeding strategy of dairy cows. Within the Amazing Grazing project, during the grazing season of 2019 grazing activity of the herd of 5 farms was recorded. Sensors were used to estimate daily grass intake per herd during the period cows were in the paddock. A pilot was performed to test (1) whether it was possible to collect all required data and calculate the estimated grass intake at herd level on a daily basis and (2) to find out how the farmers experienced this parameter in terms of reliability, accuracy, availability and added value in their management. Overall the added value was acknowledged by the farmers and further development was encouraged.
    Moderate pollination limitation in some entomophilous crops of Europe
    Holland, John M. ; Sutter, Louis ; Albrecht, Matthias ; Jeanneret, Philippe ; Pfister, Sonja C. ; Schirmel, Jens ; Entling, Martin H. ; Kaasik, Riina ; Kovacs, Gabriella ; Veromann, Eve ; Bartual, Agustín M. ; Marini, Simone ; Moonen, Anna Camilla ; Szalai, Márk ; Helsen, Herman ; Winkler, Karin ; Lof, Marjolein E. ; Werf, Wopke van der; McHugh, Niamh M. ; Smith, Barbara M. ; Wallis, David W. ; Cresswell, James E. - \ 2020
    Agriculture, Ecosystems and Environment 302 (2020). - ISSN 0167-8809
    Agroecology - Crop yield - Entomophilous crops - Landscape ecology - Pollination - Pollinators

    Pollination services to crops may be worsening because of declines in farmland pollinators, but the consequences for yields have been uncertain. We therefore investigated pollination limitation in four entomophilous crops (oilseed rape, sunflower, pears and pumpkin) by quantifying the difference in harvestable mass between open-pollinated and saturation-pollinated (hand-pollinated) flowers. We also examined whether pollination limitation in the four crops was associated with the number of flower visits by insects. Across 105 commercial fields in six European countries, the average decrease in harvestable mass due to pollination limitation was 2.8 % (SE = 1.15). Among crops, the highest decreases were in sunflowers (8%) and in one of three oilseed rape production regions (6%). We observed substantial variation among crops in the numbers of insect visits received by flowers, but it did not significantly correspond with the levels of pollination limitation. Our results suggest that yields in these crops were not severely pollination-limited in the regions studied and that other factors besides visitation by pollinators influenced the degree of pollination limitation.

    Development of offshore seaweed farming: ecology & cultivation : Synthesis report 2019
    Bernard, M.S. ; Jansen, H. ; Werf, A. van der; Meer, I. van der; Tonk, Linda - \ 2020
    Yerseke : Wageningen Marine Research (Wageningen Marine Research report C054/20) - 31
    The upscaling of offshore wind farms in the North Sea creates opportunities for seaweed aquaculture that has the potential to meet part of future resource needs, provided that it is done sustainably. Here a follow-up study of the MIP project in 2018 “Development of Offshore Seaweed Cultivation: food safety, cultivation, ecology and economy” with a focus on ecology and cultivation is presented. In order to ensure a sustainable development of seaweed farming in Dutch offshore and coastal regions in the future, it is essential to collect empirical data on the interaction of seaweed cultivation with marine ecosystems for realistic impact assessments. In subproject 1 “Ecology – Fauna associated with seaweed aquaculture in the North Sea Farm” ecosystem services and impacts of seaweed farming in the North Sea were investigated on the basis of biodiversity, a key parameter for the functioning of ecosystems. Therefore in 2019 the associated fauna on growing seaweed biomass (Saccharina latissima) and cultivation ropes was assessed at the North Sea Farm. A high number of individuals was detected on the seaweeds and cultivation ropes in general (up to 7679 individuals per rope), but species richness was low. Abundance in fauna increased from May to June and all detected species are also known from other hard substrates in the North Sea. Compared to previous assessments of biodiversity with eDNA metabarcoding at the same site, the biodiversity detected in 2019 was very low. However, biodiversity levels may differ from year to year. Moreover, the samples were not taken at the same time points and are therefore not directly comparable and the methodology only included organisms that could be collected by hand (visible to the eye) with a focus on fauna attached to the rope and kelp. It is advised to combine classical morphological biodiversity assessment and eDNA metabarcoding in future assessments to compare results in order to determine the best-suited methodology for biodiversity assessments. Biodiversity in the seaweed farm should be assessed repeatedly every 5 years to check for temporal alterations in fauna composition, especially when cultivation structures, such as anchors, are deployed throughout several years. In subproject 2 “Cultivation” seasonal variation in biomass productivity and chemical composition of kelp was evaluated in order to determine the optimal time point for harvesting in relation to the desired end product. Biomass production at the test-farm was very low in 2019, compared to previous years and a seaweed farm test location near Helgoland in the North Sea. Below 4m environmental conditions for growth were unfavourable (mainly light limitation) for Saccharina latissima. Both in 2018 and 2019 large differences in standing crops over time and depth were observed. Contrary, true protein levels varied only slightly over time. If protein is the target product, final biomass yield of S. latissima will determine the profitability of the mariculture. A combination of economic analyses and growth experiments may assist in determining the optimal cultivation technique. The 2018 experiments performed at the North Sea Farm showed large seasonal variability in the chemical composition of seaweed tissue, and high amounts of nitrogen-containing compounds besides proteins variations. Therefore in 2019, nitrogen, starch and nitrate content in the seaweed tissue were analysed. Nitrate content in S. latissima varied throughout the season and could not fully explain the difference between N measured by Dumas and true protein content in the 2019 samples. Therefore, other seaweed components containing nitrogen must explain this variation, e.g. its accumulation in cellular nitrate pools. As a final note, in order to improve the understanding of environmental conditions in the farm it is recommended that nitrate and phosphate concentrations, two essential macronutrients for growth in seaweeds, should be assessed in the water column at different depths and time points.
    Natuur Impuls Oosterschelde : Toepassingsmogelijkheden van slibrijk sediment voor natuurbouw
    Ysebaert, Tom ; Walles, Brenda ; Werf, Jebbe van der; Vet, Lodewijk de; Hansen, Jill ; Duren, Luca van; Smit, Jaco de; Bouma, Tjeerd ; Stronkhorst, Joost - \ 2020
    Yerseke : Wageningen Marine Research (Wageningen Marine Research report C038/20) - 137
    Do Locals Have a Say? Community Experiences of Participation in Governing Forest Plantations in Tanzania
    Degnet, M.B. ; Werf, E. van der; Ingram, V.J. ; Wesseler, J.H.H. - \ 2020
    Forests 11 (2020)7. - ISSN 1999-4907
    As large-scale forest plantations expand in developing countries, concerns are rising about their relation to and integration with adjacent local communities. In developing countries with weak enforcement of property rights, private plantations are more likely than state-owned plantations to involve villagers in plantation’s activities in order to secure and guarantee their access to land and labor resources. Certification standards of the Forest Stewardship Council (FSC) and adherence to responsible investment guidelines further strengthen this likelihood by requiring plantations to consult and engage local communities. Using household data from Tanzania, we assess households’ experiences with their participation in plantation activities by comparing the experiences of households in villages adjacent to private, FSC-certified plantations with those of households in villages adjacent to a non-certified, state-owned plantation. Our quantitative analyses show that households in the villages adjacent to the private, certified plantations are more likely to report to participate in plantation activities. Our results show that the certified plantations are more likely to respond to community complaints and grievances. We further find that male-headed households and households of plantation employees are more likely than female-headed households and households without plantation employees to participate in plantations’ activities. Our results imply that forest management certification can complement state policy approaches of sustainable forest management to enhance community participation in forest management
    Outbreak analysis with a logistic growth model shows COVID-19 suppression dynamics in China
    Zou, Yi ; Pan, Stephen ; Zhao, Peng ; Han, Lei ; Wang, Xiaoxiang ; Hemerik, Lia ; Knops, Johannes ; Werf, Wopke van der - \ 2020
    PLoS ONE 15 (2020)6. - ISSN 1932-6203 - p. e0235247 - e0235247.

    China reported a major outbreak of a novel coronavirus, SARS-CoV2, from mid-January till mid-March 2020. We review the epidemic virus growth and decline curves in China using a phenomenological logistic growth model to summarize the outbreak dynamics using three parameters that characterize the epidemic's timing, rate and peak. During the initial phase, the number of virus cases doubled every 2.7 days (range 2.2-4.4 across provinces). The rate of increase in the number of reported cases peaked approximately 10 days after suppression measures were started on 23-25 January 2020. The peak in the number of reported sick cases occurred on average 18 days after the start of suppression measures. From the time of starting measures till the peak, the number of cases increased by a factor 39 in the province Hubei, and by a factor 9.5 for all of China (range: 6.2-20.4 in the other provinces). Complete suppression took up to 2 months (range: 23-57d.), during which period severe restrictions, social distancing measures, testing and isolation of cases were in place. The suppression of the disease in China has been successful, demonstrating that suppression is a viable strategy to contain SARS-CoV2.

    Plant architectural responses in simultaneous maize/soybean strip intercropping do not lead to a yield advantage
    Li, Shuangwei ; Evers, Jochem B. ; Werf, Wopke van der; Wang, Ruili ; Xu, Zhaoli ; Guo, Yan ; Li, Baoguo ; Ma, Yuntao - \ 2020
    Annals of Applied Biology 177 (2020)2. - ISSN 0003-4746 - p. 195 - 210.
    architectural response - border row effect - growth - intercropping - land equivalent ratio

    Maize/soybean strip intercropping is a commonly used system throughout China with high crop yields at reduced nutrient input compared to sole maize. Maize is the taller crop, and due to its dominance in light capture over soybean in the intercrop, maize is expected to outperform maize in sole cropping. Conversely, soybean is the subordinate crop and intercropped soybean plants are expected to perform worse than sole soybean. Crop plants show plastic responses in plant architecture to their growing conditions to forage for light and avoid shading. There is little knowledge on plant architectural responses to growing conditions in simultaneous (non-relay) intercropping and their relationship to species yields. A two-year field experiment with two simultaneous maize/soybean intercropping systems with narrow and wide strips was conducted to characterise architectural traits of maize and soybean plants grown as intercrop and sole crops. Intercropped maize plants, especially those in border rows, had substantially greater leaf area, biomass and yield than maize plants in sole crops. Intercropped soybean plants, especially those in border rows, had lower leaf area, biomass and yield than sole soybean plants. Overall intercrop performance was similar to that of sole crops, with the land equivalent ratio (LER) being only slightly greater than one (1.03–1.08). Soybean displayed typical shade avoidance responses in the intercrop, such as greater internode elongation and changes in specific leaf area, but these responses could not overcome the consequences of the competition with the taller maize plants. Therefore, in contrast to relay intercrop systems, in the studied simultaneous maize/soybean system, plastic responses did not contribute to practically relevant increases in resource capture and yield at whole system (i.e., intercrop) level.

    Spatial scale, neighbouring plants and variation in plant volatiles interactively determine the strength of host–parasitoid relationships
    Aartsma, Yavanna ; Pappagallo, Silvia ; Werf, Wopke van der; Dicke, Marcel ; Bianchi, Felix J.J.A. ; Poelman, Erik H. - \ 2020
    Oikos 129 (2020)9. - ISSN 0030-1299 - p. 1429 - 1439.
    herbivore-induced plant volatiles - host–parasitoid interactions - insect–plant interactions - plant neighbourhood

    Species-specific responses to the environment can moderate the strength of interactions between plants, herbivores and parasitoids. However, the ways in which characteristics of plants, such as genotypic variation in herbivore induced volatiles (HIPVs) that attract parasitoids, affect trophic interactions in different contexts of plant patch size and plant neighbourhood is not well understood. We conducted a factorial field experiment with white cabbage Brassica oleracea accessions that differ in the attractiveness of their HIPVs for parasitoids, in the context of different patch sizes and presence or absence of surrounding Brassica nigra plants. Parasitism rates of experimentally introduced Pieris brassicae caterpillars and the presence of naturally occurring Pieris spp. caterpillars in the plots were assessed throughout the growing season. The abundance of Pieris caterpillars was neither affected by cabbage accession nor plot size. Later in the season, when B. nigra plants had senesced, fewer caterpillars were found on cabbage plants in plots with a B. nigra border. Parasitism rates fluctuated over the season, and were not affected by plot size. However, the B. nigra border negatively affected parasitism rates on the accession that is less attractive to the parasitoid Cotesia glomerata, but not on the more attractive accession. Our results show that plant variation in HIPVs can differentially influence herbivores and parasitoids depending on characteristics of the surrounding vegetation context. These findings underscore the importance of considering the interaction between focal plant traits and neighbourhood context to reliably predict trophic cascades.

    Field performance of different maize varieties in growth cores at natural and reduced mycorrhizal colonization : yield gains and possible fertilizer savings in relation to phosphorus application
    Wang, Xin Xin ; Werf, Wopke van der; Yu, Yang ; Hoffland, Ellis ; Feng, Gu ; Kuyper, Thomas W. - \ 2020
    Plant and Soil 450 (2020)1-2. - ISSN 0032-079X - p. 613 - 624.
    Crop - Genetic variation - In-growth cores - Landrace - Maize - Mycorrhizal colonization - Phosphorus

    Aims: The benefits of arbuscular mycorrhizal fungi (AMF) on yield and phosphorus (P) uptake of crops have commonly been studied by inoculating a single mycorrhizal fungal species in pot experiments. Yet, how the native AMF community affects the performance of different maize varieties under field conditions remains obscure. Methods: In-growth cores with and without rotation were used in three soils that differed in P application to assess shoot biomass, P uptake, and mycorrhizal colonization of three maize varietal groups, encompassing four inbred lines, 12 hybrids, and four landraces. Results: Rotating cores drastically reduced mycorrhizal colonization, biomass and P uptake for each varietal group at every P level. Performance of plants at natural mycorrhizal colonization at 30 kg P ha−1 was equal to that of reduced-mycorrhizal plants at 60 kg P ha−1, suggesting the potential for adequate mycorrhizal management to save P fertilizer. Conclusion: There were no significant differences between varietal groups for mycorrhizal responsiveness, confirming that the ability to associate with and benefit from AMF has been maintained in modern breeding. Mycorrhizal plants both exhibited higher P acquisition efficiency and higher P use efficiency than reduced-mycorrhizal plants. Disadvantages of in-growth cores should be duly considered.

    Syndromes of production in intercropping impact yield gains
    Li, Chunjie ; Hoffland, Ellis ; Kuyper, Thomas W. ; Yu, Yang ; Zhang, Chaochun ; Li, Haigang ; Zhang, Fusuo ; Werf, Wopke van der - \ 2020
    Nature Plants 6 (2020)6. - ISSN 2055-026X
    Intercropping, the simultaneous production of multiple crops on the same field, provides opportunities for the sustainable intensification of agriculture if it can provide a greater yield per unit land and fertilizer than sole crops. The worldwide absolute yield gain of intercropping as compared with sole crops has not been analysed. We therefore performed a global meta-analysis to quantify the effect of intercropping on the yield gain, exploring the effects of crop species combinations, temporal and spatial arrangements, and fertilizer input. We found that the absolute yield gains, compared with monocultures, were the greatest for mixtures of maize with short-grain cereals or legumes that had substantial temporal niche differentiation from maize, when grown with high nutrient inputs, and using multirow strips of each species. This approach, commonly practised in China, provided yield gains that were (in an absolute sense) about four times as large as those in another, low-input intercropping strategy, commonly practised outside China. The alternative intercropping strategy consisted of growing mixtures of short-stature crop species, often as full mixtures, with the same growing period and with low to moderate nutrient inputs. Both the low- and high-yield intercropping strategies saved 16–29% of the land and 19–36% of the fertilizer compared with monocultures grown under the same management as the intercrop. The two syndromes of production in intercropping uncovered by this meta-analysis show that intercropping offers opportunities for the sustainable intensification of both high- and low-input agriculture.
    Optimum strip width increases dry matter, nutrient accumulation, and seed yield of intercrops under the relay intercropping system
    Raza, Muhammad Ali ; Feng, Ling Yang ; Werf, Wopke van der; Iqbal, Nasir ; Khan, Imran ; Khan, Ahsin ; Din, Atta Mohi Ud ; Naeem, Muhammd ; Meraj, Tehseen Ahmad ; Hassan, Muhammad Jawad ; Khan, Aaqil ; Lu, Feng Zhi ; Liu, Xin ; Ahmed, Mukhtar ; Yang, Feng ; Yang, Wenyu - \ 2020
    Food and Energy Security 9 (2020)2. - ISSN 2048-3694
    competition ratio - growing space - maize - relay intercropping - soybean

    Strip width management is a critical factor for producing higher crop yields in relay intercropping systems. A 2-year field experiment was carried out during 2012 and 2013 to evaluate the effects of different strip width treatments on dry-matter production, major-nutrient (nitrogen, phosphorus, and potassium) uptake, and competition parameters of soybean and maize in relay intercropping system. The strip width (SW) treatments were 0.40, 0.40, and 0.40 m (SW1); 0.40, 0.40, and 0.50 m (SW2); 0.40, 0.40, and 0.60 m (SW3); and 0.40, 0.40, and 0.70 m (SW4) for soybean row spacing, maize row spacing, and spacing between soybean and maize rows, respectively. As compared to sole maize (SM) and sole soybean (SS), relay-intercropped maize and soybean accumulated lower quantities of nitrogen, phosphorus, and potassium in all treatments. However, maize in SW1 accumulated higher nitrogen, phosphorus, and potassium than SW4 (9%, 9%, and 8% for nitrogen, phosphorus, and potassium, respectively). Soybean in SW3 accumulated 25% higher nitrogen, 33% higher phosphorus, and 24% higher potassium than in SW1. The improved nutrient accumulation in SW3 significantly increased the soybean dry matter by 19%, but slightly decreased the maize dry matter by 6% compared to SW1. Similarly, SW3 increased the competition ratio value of soybean (by 151%), but it reduced the competition ratio value of maize (by 171%) compared to SW1. On average, in SW3, relay-cropped soybean produced 84% of SS seed yield and maize produced 98% of SM seed yield and achieved the land equivalent ratio of 1.8, demonstrating the highest level in the world. Overall, these results suggested that by selecting the appropriate strip width (SW3; 0.40 m for soybean row spacing, 0.40 m maize row spacing, and 0.60 m spacing between soybean and maize rows), we can increase the nutrient uptake (especially nitrogen, phosphorus, and potassium), dry-matter accumulation, and seed yields of relay-intercrop species under relay intercropping systems.

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