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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    Gridded Hourly Temperature, Radiation and Makkink Potential Evaporation forcing for hydrological modelling in the Rhine basin
    Osnabrugge, B. van; Weerts, A.H. - \ 2018
    climatology - forcing - hydrological modelling - Makkink potential evaporation - radiation - Rhine basin - temperature
    Hourly gridded observation based estimates for energy related meteorological forcing variables for a gridded hydrological model of the Rhine basin: temperature, radiation and makkink potential evaporation.
    Poly(acrylamide)-MWNTs hybrid hydrogel with extremely high mechanical strength
    Feng, Huanhuan ; Zheng, Tingting ; Wang, Xuezhen ; Wang, Huiliang - \ 2016
    Open Chemistry 14 (2016)1. - ISSN 2391-5420 - p. 150 - 157.
    CNTs - high-strength - hydrogels - radiation

    Poly(acrylamide)-multiwalled carbon nanotubes (PAAm-MWNTs) hybrid hydrogels were prepared through the radiation-induced polymerization and crosslinking of the aqueous solution of acrylamide and well-dispersed MWNTs for the first time. The PAAm gels obtained by the radiation-induced polymerization and cosslinking showed very high mechanical strengths, and the PAAm-MWNTs hybrid hydrogels had improved mechanical properties compared with the PAAm gels, and hence the PAAm-MWNTs hybrid hydrogels showed extremely high compressive and tensile strengths. The hybrid hydrogels with water contents more than 80 wt.% usually did not fracture even at compressive strengths close to or even more than 60 MPa and strains more than 97%. And the hybrid hydrogels had very high elongations (more than 2000% in some cases), especially when the water content was high. The tensile strengths were in sub-MPa. The hybrid PAAm-MWNTs hydrogel is one of the strongest hydrogel even made.

    Examining growth, yield and bean quality of Ethiopian coffee trees : towards optimizing resources and tree management
    Bote, Adugna - \ 2016
    Wageningen University. Promotor(en): Niels Anten, co-promotor(en): Jan Vos; F.L. Ocho. - Wageningen : Wageningen University - ISBN 9789462578319 - 138
    coffea - coffea arabica - trees - growth - yields - quality - radiation - nitrogen - agroecosystems - coffea - coffea arabica - bomen - groei - opbrengsten - kwaliteit - straling - stikstof - agro-ecosystemen

    Coffee (Coffeaarabica L.)bean production and quality are determined by a diversity of interacting factors (e.g. shade, nitrogen, crop traits). Bean yield increases with increase in radiation, but adequate fertilizer suppliesare needed to sustain the productivity. This thesis analysed coffee tree growth, bean production and bean quality in relation to different degrees of exposure to radiation and nitrogen supply. Growth of leaves and branches and properties of leaves such as specific leaf area, nitrogen content per unit leaf area and light-saturated rate of photosynthesis were determined. Radiation interception and nitrogen uptake were also determined as were radiation use efficiency and apparent nitrogen recovery. Tree biomass and coffee bean yield responded positively to both radiation and nitrogen supply. Abundant bean yield to the detriment of vegetative growth, however, resultedin biennial bearing in coffee trees. Effects of fruit load on coffee treegrowth and productivity were studied for two consecutive years and the resultshowed that competition between fruit growth and vegetative growth predisposed the trees for biennial bearing. Reduced vegetative growth when fruit load is high reduces the number of flower bearing nodes and hence yields in the next season. Coffee quality is a sum of favourable characteristics that satisfies requirements of different actors in the coffee chain and is the factor determining the price on the coffee market. This study has also examined coffee quality attributes in relation to radiation and nitrogen, fruit load manipulation, and genotype by environment (different altitudes) interactions. The result indicated that factors and conditions that support non-limiting supply of resources for bean to grow and a sufficient long period of maturation promote coffee bean quality. Overall, the study gained further understanding of coffee tree growth, yield and bean quality responses to aforementioned factors and explored traits that underlie the patterns. Further works are required to use the traits and describe the behaviour of coffee trees in different agro-ecosystems.

    Resource use efficiency, ecological intensification and sustainability of intercropping systems
    Mao, L. ; Zhang, L. ; Zhang, S. ; Evers, J.B. ; Werf, W. van der; Wang, J. ; Sun, H. ; Su, Z. ; Spiertz, J.H.J. - \ 2015
    Journal of Integrative Agriculture 14 (2015)8. - ISSN 2095-3119 - p. 1542 - 1550.
    growth - maize - yield - wheat - water - agriculture - radiation - capture - cotton - model
    The rapidly growing demand for food, feed and fuel requires further improvements of land and water management, crop productivity and resource-use efficiencies. Combined field experimentation and crop growth modelling during the past five decades made a great leap forward in the understanding of factors that determine actual and potential yields of monocrops. The research field of production ecology developed concepts to integrate biological and biophysical processes with the aim to explore crop growth potential in contrasting environments. To understand the potential of more complex systems (multi-cropping and intercropping) we need an agro-ecosystem approach that integrates knowledge derived from various disciplines: agronomy, crop physiology, crop ecology, and environmental sciences (soil, water and climate). Adaptation of cropping systems to climate change and a better tolerance to biotic and abiotic stresses by genetic improvement and by managing diverse cropping systems in a sustainable way will be of key importance in food security. To accelerate sustainable intensification of agricultural production, it is required to develop intercropping systems that are highly productive and stable under conditions with abiotic constraints (water, nutrients and weather). Strategies to achieve sustainable intensification include developing tools to evaluate crop growth potential under more extreme climatic conditions and introducing new crops and cropping systems that are more productive and robust under conditions with abiotic stress. This paper presents some examples of sustainable intensification management of intercropping systems that proved to be tolerant to extreme climate conditions.
    Workshop gewasgezondheid en vruchtkwaliteit bij vochtig telen : kennisuitwisseling teeltadviseurs
    Gelder, Arie de - \ 2015
    horticulture - greenhouse horticulture - cucumis - rosa - crop quality - workshops (programs) - moisture content - mycosphaerella - radiation - evaporation - temperature - lighting - production
    Study of a prototypical convective boundary layer observed during BLLAST: contributions by large-scale forcings
    Pietersen, H.P. ; Vilà-Guerau De Arellano, J. ; Augustin, P. ; Boer, A. van de; Coster, O. de; Delbarre, H. ; Durand, P. ; Fourmentin, M. ; Gioli, B. ; Hartogensis, O.K. ; Lohou, F. ; Lothon, M. ; Ouwersloot, H.G. ; Pino, D. ; Reuder, J. - \ 2015
    Atmospheric Chemistry and Physics 15 (2015). - ISSN 1680-7316 - p. 4241 - 4257.
    large-eddy simulation - turbulence - entrainment - transition - radiation - decay
    We study the influence of the large-scale atmospheric contribution to the dynamics of the convective boundary layer (CBL) in a situation observed during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. We employ two modeling approaches, the mixed-layer theory and large-eddy simulation (LES), with a complete data set of surface and upper-air atmospheric observations, to quantify the contributions of the advection of heat and moisture, and subsidence. We find that by only taking surface and entrainment fluxes into account, the boundary-layer height is overestimated by 70 %. Constrained by surface and upper-air observations, we infer the large-scale vertical motions and horizontal advection of heat and moisture. Our findings show that subsidence has a clear diurnal pattern. Supported by the presence of a nearby mountain range, this pattern suggests that not only synoptic scales exert their influence on the boundary layer, but also mesoscale circulations. LES results show a satisfactory correspondence of the vertical structure of turbulent variables with observations. We also find that when large-scale advection and subsidence are included in the simulation, the values for turbulent kinetic energy are lower than without these large-scale forcings. We conclude that the prototypical CBL is a valid representation of the boundary-layer dynamics near regions characterized by complex topography and small-scale surface heterogeneity, provided that surface- and large-scale forcings are representative for the local boundary layer.
    Interactions between aerosal and convective boundary-layer dynamics over land
    Wilde Barbaro, E. - \ 2015
    Wageningen University. Promotor(en): Maarten Krol; Bert Holtslag, co-promotor(en): Jordi Vila-Guerau de Arellano. - Wageningen : Wageningen University - ISBN 9789462572652 - 182
    aërosolen - atmosferische grenslaag - grenslaagmeteorologie - aardoppervlak - modellen - simulatiemodellen - straling - atmosfeer - aerosols - atmospheric boundary-layer - boundary-layer meteorology - land surface - models - simulation models - radiation - atmosphere

    In this Section, we summarize the most important findings and relevant issues treated in detail in Chapters 2 to 5.

    The primary conclusion of this thesis is that it is necessary to take aerosols into account to accurately describe the convective atmospheric boundary-layer (CBL) dynamics and the land-surface processes. We reached this conclusion by systematically studying the land-CBL system and its couplings, and employed a hierarchy of models ranging from an eddy-resolving model (large-eddy simulation; LES) to non-eddy resolving models (mixed-layer model, and single column model). In addition to the numerical component, we used a complete observational data set to help us design and evaluate our numerical framework.

    Chapter 2 was devoted to the explanation of the radiative transfer code used in Chapters 4 and 5. We showed that despite the simplified treatment of solar radiation and its interactions with aerosols, our radiative code is in general agreement with a more sophisticated radiative transfer code, even for extreme aerosol loads. Moreover, our results reproduce observations of direct and diffuse radiation at the surface accordingly - as shown in Chapter 4.

    Regarding the longwave band, we showed that aerosols are not relevant for the estimation of the incoming longwave radiation at the surface. We concluded that Brunt's formula, depending only on screen level temperature and vapor pressure, is the most adequate to represent the incoming longwave radiation at the surface for the cases relevant for our studies.

    In Chapter 3 we investigated the impact of aerosol heat absorption on the dynamics of an idealized CBL with prescribed surface fluxes. We found that the structure and evolution of the CBL were influenced by the vertical distribution of the aerosols. Moreover, we showed that the aerosols influence the exchange of heat between the CBL and the free troposphere by (i) extinction of radiation and consequently reduced surface fluxes, and by (ii) deepening the entrainment zone depth. We highlighted the importance of high-resolution models to properly represent the effects of aerosol absorption of radiation on the dynamics of the CBL, especially in the entrainment zone. We demonstrated that, in addition to the properties of the aerosols, the vertical distribution is an important characteristic to properly describe the CBL height evolution and the dynamics of the upper part of the CBL. To further support the analysis of the LES results, we used a mixed-layer (MXL) model to calculate boundary-layer depth and the potential temperature jump at the inversion layer. In spite of the simplicity of this model, the mixed-layer results obtained for boundary-layer height and the inversion layer jump agreed well with the LES results.

    Extending the knowledge acquired with the academical prototypical experiments performed in Chapter 3, in Chapter 4 we quantified the effects of aerosol scattering and absorption of shortwave (SW) radiation both on the surface energy budget and on the CBL dynamics. To this end, we coupled our LES model and the MXL model to (i) a land-surface model and (ii) a broadband SW radiative transfer model, (described in Chapter 2). We successfully validated the results obtained with the LES model and MXL model using measurements of (thermo)dynamic variables and aerosol properties observed in Cabauw (the Netherlands). Our LES results showed that for Cabauw (over well-watered grassland) aerosols significantly alter the magnitude of the available energy at the surface and its partitioning. Under well-watered conditions, the sensible heat flux was more strongly reduced compared to the latent heat flux. Given the satisfactory agreement between the LES results and MXL model results, we further explored the sensitivity of the land-CBL system to a wide range of aerosol optical depths and single scattering albedos using the MXL model. Our results showed that higher loads of aerosols impose an energy restriction at the surface. As a result, we calculated a delay in the morning onset of the CBL and an advance in the CBL afternoon collapse. We also found that entrainment of aerosols from the residual layer plays a significant role in the development of the CBL dynamics during the day. An important aspect of Chapter 4 is the investigation of the different responses of the CBL dynamics depending on aerosol optical properties. Strongly absorbing aerosols deepened and warmed the CBL, while purely scattering aerosols shallowed and cooled the CBL.

    We highlighted that the results presented in Chapter 4 can be used as a benchmark to evaluate coupling and performance of the parametrizations for SW radiation, land-surface and boundary-layer schemes, implemented in mesoscale or global chemistry transport models.

    In Chapter 5 we increased the complexity of our land-CBL system representation by studying the formation and transport of ammonium nitrate aerosols. In doing so, we coupled in our LES radiation, chemistry, aerosols, CBL dynamics, and surface exchange processes of chemicals, heat and moisture. Our fully coupled LES model was again evaluated against observations of chemistry and aerosol fields and showed a good correspondence. In particular, our results showed a satisfactory agreement between the simulated and observed nitrate partitioning at the surface.

    We showed that gas-aerosol conversion of nitrate leads to highly non-linear profiles of nitrate concentrations and turbulent fluxes. Moreover, the shapes of the simulated profiles depended strongly on the time scale of gas-aerosol conversions. Note that the typical timescale of turbulent motions in the CBL is around 10-20 minutes. For shorter time scales of gas-aerosol conversion compared to the CBL dynamics timescale, we found that turbulent fluxes are larger and concentration profiles more tilted within the CBL. These results have a significant impact on the nitrate deposition flux at the surface. Our LES results confirmed that the large deposition velocities for aerosol nitrate close to the surface are actually due to outgassing of aerosol nitrate rather than a real deposition process.

    An important aspect discussed in Chapter 5 concerns the inability of non-eddy resolving models to accurately model the turbulent transport of nitrate within the CBL. Based on a detailed analysis of the flux budget equation, we showed that the exchange coefficient of heat used in our 1D model has to be increased to better account for the complex interaction between gas-aerosol conversion of nitrate and 3D turbulence within the CBL. Indeed, the new exchange coefficient also improved the comparison between gas-aerosol partitioning of nitrate calculated with our 1D model and surface observations.

    The results discussed in this thesis demonstrate the need for considering the influence of aerosols on the CBL dynamics. Specifically, aerosols influence important phenomena for the CBL evolution namely radiation, surface-atmosphere interactions, chemistry, and (thermo)dynamics. In addition to that, the availability of high-resolution numerical simulations is crucial to validate and evaluate results obtained by numerical models that do not explicitly resolve the turbulent field.

    Improving radiation use efficiency in greenhouse production systems
    Li, Tao - \ 2015
    Wageningen University. Promotor(en): Leo Marcelis, co-promotor(en): Ep Heuvelink. - Wageningen : Wageningen University - ISBN 9789462572577 - 156
    glastuinbouw - kassen - gewasfysiologie - agrarische productiesystemen - gewasproductie - stralingsbenuttigingsefficiëntie - straling - fotosynthese - licht - gebruiksefficiëntie - greenhouse horticulture - greenhouses - crop physiology - agricultural production systems - crop production - radiation use efficiency - radiation - photosynthesis - light - use efficiency


    A large increase in agricultural production is needed to feed the increasing world population with their increasing demand per capita. However, growing competition for arable land, water, energy, and the degradation of the environment impose challenges to improve crop production. Hence agricultural production efficiency needs to increase. Greenhouses provide the possibility to create optimal growth conditions for crops, thereby improving production and product quality. Light is the driving force for plant photosynthesis and in greenhouse horticulture, light is often the most limiting factor for plant growth. Therefore, improving radiation use efficiency (RUE) in greenhouse production systems is imperative in order to improve plant growth and production. The objective of this thesis is to obtain insight in improving RUE in greenhouse production systems through better understanding of crop physiology. Three aspects related to RUE have been studied in this thesis, 1) improving light distribution in the crop canopy; 2) allowing more light in the greenhouse during summer; and 3) balancing the source and sink strength during plant growth.

    Light is heterogeneously distributed in the crop canopy. Due to the saturating response of leaf photosynthesis rate to light, a more homogeneous light distribution in the canopy will result in a higher crop photosynthesis. In Chapter 2, the effect of diffuse glass on spatial light distribution in a fully developed tomato canopy and its direct and indirect effects on crop photosynthesis were explored. Diffuse glass, which transforms a portion of direct solar light into diffuse light without influencing the light transmissivity of the glass, was applied as greenhouse cover. Under diffuse glass cover, light was more evenly distributed (in both horizontal and vertical direction) within the canopy compared with plants grown under conventional clear glass cover. Besides a more uniform light distribution, diffuse glass also resulted in higher leaf photosynthetic capacity in the middle of the crop canopy and in a higher leaf area index (LAI). The higher leaf photosynthetic capacity was positively correlated with a higher leaf total nitrogen and chlorophyll content. Moreover, lower leaf temperature and less photo-inhibition of top canopy leaves were observed under diffuse glass cover when global radiation was high. Total crop photosynthesis between 1st April and 1st October was enhanced by 7.2 % under diffuse glass. This enhancement mainly resulted from four factors (in order of decreasing importance): a more homogeneous horizontal light distribution, a higher leaf photosynthetic capacity, a more uniform vertical light distribution and a higher LAI.

    In summer growers of shade tolerant pot-plants often apply shading screens in the greenhouse or white wash on the greenhouse cover in order to avoid leaf or flower damage caused by high light. Shading carries a penalty on potential crop growth which is positively related to the amount of light that can be captured. Considering the advantageous properties of diffuse glass cover, i.e. a more homogeneous light distribution, a lower leaf temperature and less photo-inhibition when global radiation is high, in Chapter 3 we tested the feasibility of allowing more light (i.e. less shading) via diffuse glass cover for cultivation of shade tolerant pot-plants during summer. Two Anthurium andreanum cultivars (Pink Champion and Royal Champion) were grown in 3 greenhouse compartments. Under similar DLI [7.5 mol m-2 d-1 PAR (photosynthetic active radiation)], diffuse glass cover resulted in 8 % higher crop RUE (i.e. dry mass production per unit intercepted light) in ‘Royal Champion’ compared with clear glass cover treatment, which consequently resulted in higher total biomass production. This effect was not observed in ‘Pink Champion’. Under diffuse glass cover, high DLI (10 mol m-2 d-1 PAR) resulted in 20-23 % higher total biomass production in both cultivars compared with low DLI (7.5 mol m-2 d-1 PAR), this mainly resulted from the higher cumulative intercepted light. No flower or leaf damage was observed in these treatments. High DLI even resulted in more compact plants as indicated by a higher ratio of aboveground fresh mass to plant height.

    In Chapter 4, we addressed a question resulting from Chapter 3, i.e. why the stimulating effect of diffuse light on crop RUE in anthurium pot-plants is cultivar specific? We excluded the fraction of canopy light interception and steady-state leaf photosynthesis as potential explanations, and explained it from instantaneous leaf photosynthesis which closely correlates with the temporal light distribution. Diffuse glass cover smoothed the variation of temporal light distribution at a given point on a leaf during a clear day, which consequently resulted in less temporal variation of stomatal conductance in ‘Royal Champion’ which had stomata showing a fast-response to the variation in light intensity. As stomata are the gateway for CO2 uptake, less variation in stomatal conductance imposed less limitation for leaf photosynthesis under diffuse glass cover, thereby resulting in a higher crop RUE. For ‘Pink Champion’, however, stomata were less responding to variations in light intensity. Therefore, stomata imposed only a marginal limitation on leaf photosynthesis even under clear glass cover where the temporal incident light intensity varied substantially due to the shadow cast by the greenhouse construction parts and equipment.

    Application of supplementary assimilation light in greenhouses is rapidly increasing. The beneficial effect of supplementary assimilation light is determined by the balance between assimilate production in source leaves and the overall capacity of the plant to use these assimilates. Therefore, it is important to identify the source-sink balance during plant growth. In Chapter 5, three tomato cultivars with different potential fruit size [‘Komeett’ (large size); ‘Capricia’ (medium size); ‘Sunstream’ (small size, cherry tomato)] were grown under commercial crop management. We estimated the source-sink ratio from the early growth stage to fully fruiting stage through experimentation and model simulation. Carbohydrate content of leaves and stems were periodically determined. Tomato plants showed a period of sink limitation (‘Komeett’ and ‘Capricia’) or came close to sink limitation (‘Sunstream’) during the early growth stage under ample natural irradiance (early September) as indicated by a source-sink ratio higher than or close to 1. Fruiting tomato plants were source-limited as indicated by an extremely low source-sink ratio (average source-sink ratio from 50 days after planting onwards was 0.17, 0.22 and 0.33 for ‘Komeett’, ‘Capricia’ and ‘Sunstream’, respectively). During the fully fruiting stage, the source-sink ratio was negatively correlated with the potential fruit size when commercial fruit load was maintained. Carbohydrate content in tomato stems and leaves increased linearly with plant source-sink ratio.

    The experiments and results described in this thesis provide insights for improving RUE in greenhouse production systems. The main achievements and limitations as well as practical applications are discussed in Chapter 6.

    Temporal and spatial variability of urban heat island and thermal comfort within the Rotterdam agglomeration
    Hove, B. van; Jacobs, C.M.J. ; Heusinkveld, B.G. ; Elbers, J.A. ; Driel, B.L. van; Holtslag, A.A.M. - \ 2015
    Building and Environment 83 (2015). - ISSN 0360-1323 - p. 91 - 103.
    klimaatverandering - temperatuur - perceptie - stedelijke gebieden - ruimtelijke variatie - variatie in de tijd - rotterdam - climatic change - temperature - perception - urban areas - spatial variation - temporal variation - rotterdam - air-temperature - street geometry - canyon geometry - climate zones - land-use - environment - areas - radiation - impact - fluxes
    This paper reports on temporal and spatial variability of local climate and outdoor human thermal comfort within the Rotterdam agglomeration. We analyse three years of meteorological observations (2010–2012) from a monitoring network. Focus is on the atmospheric urban heat island (UHI); the difference in air temperature between urban areas and rural surroundings. In addition, we calculate the Physiologically Equivalent Temperature (PET) which is a measure of thermal comfort. Subsequently, we determine the dependency of intra-urban variability in local climate and PET on urban land-use and geometric characteristics. During a large part of the year, UHI-intensities in densely built areas can be considerable, under calm and clear (cloudless) weather conditions. The highest maximum UHI-values are found in summer, with 95-percentile values ranging from 4.3 K to more than 8 K, depending on the location. In winter, UHI-intensities are generally lower. Intra-urban variability in maximum UHI-intensity is considerable, indicating that local features have an important influence. It is found to be significantly related to building, impervious and green surface fractions, respectively, as well as to mean building height. In summer, urban areas show a larger number of discomfort hours (PET > 23 °C) compared to the reference rural area. Our results indicate that this is mainly related to the much lower wind velocities in urban areas. Also intra-urban variability in thermal comfort during daytime appears to be mainly related to differences in wind velocity. After sunset, the UHI effect plays a more prominent role and hence thermal comfort is more related with urban characteristics.
    Estimation of the refractive index structure parameter from single-level daytime routine weather data
    Boer, A. van de; Moene, A.F. ; Graf, A. ; Simmer, C. ; Holtslag, A.A.M. - \ 2014
    Applied Optics 53 (2014)26. - ISSN 1559-128X - p. 5944 - 5960.
    obukhov similarity functions - water-vapor - optical turbulence - sonic anemometer - surface fluxes - energy-balance - temperature - radiation - land - heat
    Atmospheric scintillations cause difficulties for applications where an undistorted propagation of electromagnetic radiation is essential. These scintillations are related to turbulent fluctuations of temperature and humidity that are in turn related to surface heat fluxes. We developed an approach that quantifies these scintillations by estimating Cn2 from surface fluxes that are derived from single-level routine weather data. In contrast to previous methods that are biased to dry and warm air, our method is directly applicable to several land surface types, environmental conditions, wavelengths, and measurement heights (lookup tables for a limited number of site-specific parameters are provided). The approach allows for an efficient evaluation of the performance of, e.g., infrared imaging systems, laser geodetic systems, and ground-to-satellite optical communication systems.We tested our approach for two grass fields in central and southern Europe, and for a wheat field in central Europe. Although there are uncertainties in the flux estimates, the impact on Cn2 is shown to be rather small. The Cn2 daytime estimates agree well with values determined from eddy covariance measurements for the application to the three fields. However, some adjustments were needed for the approach for the grass in southern Europe because of non-negligible boundary-layer processes that occur in addition to surface-layer processes.
    Simulating potential growth and yield of oil palm (Elaeis guineensis) with PALMSIM: Model description, evaluation and application
    Hoffmann, M. ; Castaneda Vera, A. ; Wijk, M.T. van; Giller, K.E. ; Oberthür, T. ; Donough, C. ; Whitbread, A.M. - \ 2014
    Agricultural Systems 131 (2014). - ISSN 0308-521X - p. 1 - 10.
    crop production - productivity - radiation - systems
    Reducing the gap between water-limited potential yield and actual yield in oil palm production systems through intensification is seen as an important option for sustainably increasing palm oil production. Simulation models can play an important role in quantifying water-limited potential yield, and therefore the scope for intensification, but no oil palm model exists that is both simple enough and at the same time incorporates sufficient plant physiological knowledge to be generally applicable across sites with different growing conditions. The objectives of this study therefore were to develop a model (PALMSIM) that simulates, on a monthly time step, the potential growth of oil palm as determined by solar radiation and to evaluate model performance against measured oil palm yields under optimal water and nutrient management for a range of sites across Indonesia and Malaysia. The maximum observed yield in the field matches the corresponding simulated yield for dry bunch weight with a RMSE of 1.7 Mg ha-1 year-1 against an observed yield of 18.8 Mg ha-1. Sensitivity analysis showed that PALMSIM is robust: simulated changes in yield caused by modifying the parameters by 10% are comparable to other tree crop model evaluations. While we acknowledge that, depending on the soils and climatic environment, yields may be often water limited, we suggest a relatively simple physiological approach to simulate potential yield, which can be usefully applied to high rainfall environments and is considered as a first step in developing an oil palm model that also simulates water-limited potential yield. To illustrate the application possibilities of the model, PALMSIM was used to create a potential yield map for Indonesia and Malaysia by simulating the growth and yield at a resolution of 0.1°. This map of potential yield is considered as a first step towards a decision support tool that can identify potentially productive, but at the moment degraded sites in Indonesia and Malaysia
    Introduction to the Third GEWEX Atmospheric Boundary Layer Study (GABLS3)
    Holtslag, A.A.M. - \ 2014
    Boundary-Layer Meteorology 152 (2014)2. - ISSN 0006-8314 - p. 127 - 132.
    low-level jets - diurnal cycles - land-surface - sea-ice - model - radiation - weather
    The atmospheric boundary layer (ABL) plays a dominant role in the exchange of energy, water vapour, trace gases and momentum between the earth’s surface and the overlying atmosphere. Consequently, the ABL is an important part of any numerical model in use for atmospheric and climate research, for operational weather forecasting, and for air - quality and wind - energy studies. For all these applications an overall representation is needed for boundary-layer turbulence and near-surface processes, as well as for vertical diffusion above the boundary layer. This representation is typically referred as the parametrization of vertical diffusion and turbulent mixing. It appears that models at various research groups and operational centres use rather different methods to represent turbulence and vertical diffusion and the reasons behind this diversity are not that easy to unravel. Most likely, this originates for historical reasons due to the outcome of various tuning exercises and to the num
    Forest summer albedo is sensitive to species and thinning: how should we account for this in Earth system models?
    Otto, J. ; Berveiller, D. ; Bréon, F.M. ; Delpierre, N. ; Geppert, G. ; Granier, A. ; Jans, W.W.P. ; Knohl, A. ; Schelhaas, M.J. ; Moors, E.J. - \ 2014
    Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 2411 - 2427.
    leaf-area index - boreal forest - reflectance models - canopy reflectance - carbon-cycle - climate - radiation - stands - simulations - variability
    Although forest management is one of the instruments proposed to mitigate climate change, the relationship between forest management and canopy albedo has been ignored so far by climate models. Here we develop an approach that could be implemented in Earth system models. A stand-level forest gap model is combined with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning on summertime canopy albedo. This approach reveals which parameter has the largest affect on summer canopy albedo: we examined the effects of three forest species (pine, beech, oak) and four thinning strategies with a constant forest floor albedo (light to intense thinning regimes) and five different solar zenith angles at five different sites (40° N 9° E–60° N 9° E). During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning. These trends continue until the end of the rotation, where thinning explains up to 50% of the variance in near-infrared albedo and up to 70% of the variance in visible canopy albedo. The absolute summertime canopy albedo of all species ranges from 0.03 to 0.06 (visible) and 0.20 to 0.28 (near-infrared); thus the albedo needs to be parameterised at species level. In addition, Earth system models need to account for forest management in such a way that structural changes in the canopy are described by changes in leaf area index and crown volume (maximum change of 0.02 visible and 0.05 near-infrared albedo) and that the expression of albedo depends on the solar zenith angle (maximum change of 0.02 visible and 0.05 near-infrared albedo). Earth system models taking into account these parameters would not only be able to examine the spatial effects of forest management but also the total effects of forest management on climate.
    Crop growth, light utilization and yield of relay intercropped cotton as affected by plant density and a plant growth regulator
    Mao, L. ; Zhang, L. ; Zhao, X. ; Liu, S. ; Werf, W. van der; Zhang, S. ; Spiertz, J.H.J. ; Li, Z. - \ 2014
    Field Crops Research 155 (2014). - ISSN 0378-4290 - p. 67 - 76.
    mepiquat chloride - chlorophyll content - leaf senescence - temperature - wheat - photosynthesis - architecture - performance - physiology - radiation
    Modern cotton cultivation requires high plant densities and compact plants. Here we study planting density and growth regulator effects on plant structure and production of cotton when the cotton is grown in a relay intercrop with wheat, a cultivation system that is widespread in China. Field experiments were carried out in 2010, 2011 and 2012 in Anyang, Henan province, China. Plant densities (PD) were 3.0, 4.5, 6.0 and 7.5 plants m-2, and growth regulator mepiquat chloride (MC) was applied in four different schedules. Plant density significantly affected cotton biomass, but MC did not. Aboveground biomass was linearly associated with plant density. Increasing plant density significantly increased crop light use efficiency, especially during the reproductive phase. This effect was attributed to a better light distribution in the canopy, resulting in higher crop photosynthesis. MC increased the partitioning to leaves, expressed as leaf/shoot ratio. Plant height and length of fruit branches were significantly reduced by MC, resulting in a more compact canopy. Maximum leaf area index was slightly lowered at higher MC dose, but MC did not significantly affect light interception. Plant density and MC showed a significant interaction effect on crop height, but not on leaf growth, biomass or lint yield. At high plant densities, 3–4 consecutive applications of MC improved plant architecture, resulting in a higher LUE and yield. Lint yields were about 10% higher with MC applied at a high cumulative dose with high plant densities compared to MC free control.
    Sporulation environment of emetic toxin-producing Bacillus cereus strains determines spore size, heat resistance and germination capacity
    Voort, M. van der; Abee, T. - \ 2013
    Journal of Applied Microbiology 114 (2013)4. - ISSN 1364-5072 - p. 1201 - 1210.
    wet-heat - bacterial-spores - dipicolinic acid - subtilis spores - atcc-14579 - thuringiensis - radiation - anthracis - kinetics - liquid
    Aim Heat resistance, germination and outgrowth capacity of Bacillus cereus spores in processed foods are major factors in causing the emetic type of gastrointestinal disease. In this study, we aim to identify the impact of different sporulation conditions on spore properties of emetic toxin-producing B. cereus strains. Methods and Results Spore properties of eight different emetic toxin-producing strains were tested, with spores produced in five different sporulation conditions: aerated liquid cultures, air–liquid biofilms, 1·5% agar plates, 0·75% agar plates and swarming colonies. Model food studies revealed spores from emetic toxin-producing strains to germinate efficiently on meat broth- and milk-based agar plates, whereas germination on rice-based agar plates was far less efficient. Notably, spores of all strains germinated efficiently when 0·1% meat broth was added to the rice plates. Analysis of spores derived from different environments revealed large diversity and showed biofilm spores for the strains tested to be the largest in size, the most heat resistant and with the lowest germination capacity. Conclusions Sporulation in complex conditions such as biofilms and surface swarming colonies increases heat resistance and dormancy of spores. Significance and impact of the study The results obtained imply the importance of sporulation conditions on spore properties of emetic toxin-producing B. cereus strains, as occur for instance in food processing. Keywords Bacillus cereus; biofilm; food poisoning; heat resistance; spore germination; swarming
    Greenhouse climate control affects postharvest tomato quality
    Farneti, B. ; Schouten, R.E. ; Qian, T. ; Dieleman, J.A. ; Tijskens, L.M.M. ; Woltering, E.J. - \ 2013
    Postharvest Biology and Technology 86 (2013). - ISSN 0925-5214 - p. 354 - 361.
    nutritional quality - closed greenhouse - apple fruit - temperature - yield - radiation - sweetness - cultivar - fructose - behavior
    In this study, important quality properties such as firmness, sugar and acid levels were measured and analysed in tomatoes harvested from three greenhouses during a five month period and stored at 16 degrees C for over 20 days. Tomatoes were harvested from three identical, neighbouring, greenhouses which were either conventionally ventilated (open greenhouse) or mechanically cooled (semi-closed greenhouses). Sugar and acids levels were hardly affected by greenhouse type. Compared to the open greenhouse, semi-closed greenhouses produced heavier and less mature (firmer) fruit at the commercial harvesting stage based on colour. Fruit maturity differences could be linked to the vertical temperature gradient and to CO2 levels in the different greenhouses. This indicates that CO2 levels and temperature affect the synchronisation between colour and firmness maturity at harvest. The acceptance period, i.e., the time period both tomato colour and firmness are considered acceptable by consumers, will likely be positively affected when growers switch from conventionally ventilated to semi-closed production systems. Additional to greenhouse effects also effects of the harvest month were observed. The sugar to acid ratio was highest and glucose to fructose ratio was lowest in July, the month with the highest irradiance, irrespective of greenhouse type. The estimated value for the maximum firmness (F-max) varied from 17.9 N in August to 31.2 N in June. This monthly variation in F-max explains an important part of the variation found in the postharvest behaviour of tomatoes. Interestingly, the monthly variation in F-max showed the same trend as found for the monthly initial sugar levels. It might be hypothesised that the monthly variation in glucose and fructose levels causes variation in that part of firmness that is generated by cell turgor. The monthly variation in F-max, sugar and acid levels could not be linked to climate conditions and remains to be elucidated. (C) 2013 Elsevier B.V. All rights reserved.
    Protocol to support model selection and evaluation in a modular crop modelling framework: An application for simulating crop response to nitrogen supply
    Adam, M.Y.O. ; Belhouchette, H. ; Corbeels, M. ; Ewert, F. ; Perrin, A. ; Casellas, E. ; Celette, F. ; Wery, J. - \ 2012
    Computers and Electronics in Agriculture 86 (2012). - ISSN 0168-1699 - p. 43 - 54.
    agricultural systems - growth simulation - use efficiency - radiation - wheat - software - soil - knowledge - dynamics - science
    Crop models require different structures for different applications. Modular and flexible crop modelling frameworks, such as the recently developed agricultural production and externalities simulator (APES), support the change of model structure. However, the assembly of different modules to create a model may not always result in the best model structure. We developed and tested a protocol for a systematic selection and evaluation of a crop growth model structure. The novelty of the presented protocol relies on a throughout analysis of the different modelling approaches (modules) and on how to assemble them to create new modelling solutions (i.e. model). We use a case study to demonstrate that we can explicitly express and test the different assumptions behind the choice of a specific modelling approach. Our case study refers to the simulation of crop growth in response to nitrogen management and the importance of an accurate simulation of the nitrogen uptake. Applying the proposed protocol, we identify the need to improve the initially selected nitrogen mineralisation module. We conclude that not only is the protocol suitable to provide guidance for systematic testing of different crop processes modelled, but also its use highlights the importance of the documentation of the modelling process and of the clarification of the uncertainty associated with the model structure.
    Warming impacts on winter wheat phenophase and grain yield under field conditions in Yangtze Delta Plain, China
    Tian, Y.L. ; Chen, J. ; Chen, C.Q. ; Deng, A.X. ; Song, Z.W. ; Zheng, C.Y. ; Hoogmoed, W.B. ; Zhang, W.J. - \ 2012
    Field Crops Research 134 (2012). - ISSN 0378-4290 - p. 193 - 199.
    dry-matter - temperature - trends - radiation - growth
    A five-year experiment with Free Air Temperature Increase facility was conducted to investigate the actual responses of winter wheat phenophase and yield to warming in Yangtze Delta Plain, China. Air temperature increase of around 1.5 degrees C in wheat canopy advanced crop phenophases significantly, leading to a reduction in length of the entire growth period by 10 days (P<0.05). This reduction was mainly found in the length of pre-anthesis phase, while the length of post-anthesis phase was prolonged slightly. Warming increased grain yield by 16.3% (P
    Vertebrate time-tree elucidates the biogeographic pattern of a major biotic change around the K-T boundary in Madagascar
    Crottinia, A. ; Madsen, O. ; Poux, C. ; Straussa, A. ; Vieites, D.R. ; Vences, M. - \ 2012
    Proceedings of the National Academy of Sciences of the United States of America 109 (2012)14. - ISSN 0027-8424 - p. 5358 - 5363.
    species richness - ocean currents - dispersal - diversification - divergence - hypothesis - vicariance - phylogeny - evolution - radiation
    The geographic and temporal origins of Madagascar's biota have long been in the center of debate. We reconstructed a time-tree including nearly all native nonflying and nonmarine vertebrate clades present on the island, from DNA sequences of two single-copy protein-coding nuclear genes (BDNF and RAG1) and a set of congruent time constraints. Reconstructions calculated with autocorrelated or independent substitution rates over clades agreed in placing the origins of the 31 included clades in Cretaceous to Cenozoic times. The two clades with sister groups in South America were the oldest, followed by those of a putative Asian ancestry that were significantly older than the prevalent clades of African ancestry. No colonizations from Asia occurred after the Eocene, suggesting that dispersal and vicariance of Asian/Indian groups were favored over a comparatively short period during, and shortly after, the separation of India and Madagascar. Species richness of clades correlates with their age but those clades that have a large proportion of species diversity in rainforests are significantly more species-rich. This finding suggests an underlying pattern of continuous speciation through time in Madagascar's vertebrates, with accelerated episodes of adaptive diversification in those clades that succeeded radiating into the rainforests.
    Photosynthesis: the foundation al all production : Greenhouse plants are chemical factories
    Heuvelink, E. - \ 2012
    In Greenhouses : the international magazine for greenhouse growers 1 (2012)1. - ISSN 2215-0633 - p. 11 - 13.
    kassen - glastuinbouw - fotosynthese - zonne-instraling - kooldioxide - calvin cyclus - straling - gewasproductie - greenhouses - greenhouse horticulture - photosynthesis - insolation - carbon dioxide - calvin cycle - radiation - crop production
    All plants in the greenhouse are actually chemical factories. Photosynthesis, the foundation of all production is a complex system of processes. It's fascinating because man cannot match many of these processes, in terms of efficiency. Ironically, an important substance - an enzyme - would be trown out of most factories on grounds of inefficiency. But nature has found something fot thast too.
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