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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    We will mail you new results for this query: keywords==Calibration
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Assessing the effect of water harvesting techniques on event-based hydrological responses and sediment yield at a catchment scale in northern Ethiopia using the Limburg Soil Erosion Model (LISEM)
Grum, Berhane ; Woldearegay, Kifle ; Hessel, Rudi ; Baartman, Jantiene E.M. ; Abdulkadir, Mohammed ; Yazew, Eyasu ; Kessler, Aad ; Ritsema, Coen J. ; Geissen, Violette - \ 2017
Catena 159 (2017). - ISSN 0341-8162 - p. 20 - 34.
Calibration - Northern Ethiopia - Rain intensity - Runoff - Soil erosion
Runoff and sediment yield in semi-arid catchments are highly influenced by infrequent but very heavy rains. These events occur over short temporal scales, so runoff and sediment transport can only be understood using an event-based analysis. We applied a hydrological and soil-erosion model, LISEM, to the Gule catchment (~ 12 km2) in northern Ethiopia. The objectives of the study were: (a) to evaluate the performance of LISEM in describing event-based hydrological processes and sediment yield in a catchment under the influence of different water harvesting techniques (WHTs), and (b) to study the effect of the WHTs on catchment-scale event-based runoff and sediment yield. The model performed satisfactorily (NSE > 0.5) for most of the events when discharge was calibrated at the main outlet (Gule) and at a sub-outlet (Misbar). Runoff coefficients for the Gule catchment and Misbar sub-catchment were expectedly low due to the implementation of WHTs, which can store runoff from the rains and increase infiltration into the soil. Simulated and measured sediment yields were of similar orders of magnitude. LISEM generally overestimated sediment yield compared to the measurements. The poor performance of LISEM in predicting sediment yield could be attributed to the uncertainty of several factors controlling soil erosion and the inadequacy of LISEM in describing soil erosion on steep slopes. Catchment-scale model simulations indicated that runoff and sediment yield could be effectively reduced by implementing WHTs. The model estimated 41 and 61% reductions in runoff and sediment yield at the Gule outlet, respectively. Similarly, runoff and sediment yield at the Misbar sub-outlet were reduced by 45 and 48%, respectively. LISEM can thus be used to simulate the effects of different existing or new WHTs on catchment hydrology and sediment yield. The results of scenario predictions could be useful for land-use planners who intend to implement different measures of catchment management.
Field tests of dielectric sensors in a facility for studying salt tolerance of crops
Straten, Gerrit Van; Vos, Arjen De; Vlaming, Rik ; Oosterbaan, Roland - \ 2016
International Agricultural Engineering Journal 25 (2016)2. - ISSN 0858-2114 - p. 102 - 113.
Calibration - Electrical conductivity - Irrigation - Salinity - Salt tolerance - Soil sensor - Volumetric water content

Seven salinity levels ranging from 1.7 to 35 dS/m are applied to groups of eight fields each in a field facility for testing the salt tolerance of crops. Each of the 56 test fields is equipped with one or two dielectric sensors for soil volumetric water content (VWC) and bulk electric conductivity (ECb). Several models for calibrating the sensors in the laboratory were tested and parameterized. Overall, the root mean square error was in the range of 0.57-0.59 dS/m in terms of soil bulk EC. The models differed in their robustness against inversion to obtain pore water EC from measured bulk EC. The laboratory calibration formula overestimates the pore water EC at low EC (5 dS/m), and underestimates it at high EC (25 dS/m). In practice, calculated sensor pore water EC's in fields with the same salinity treatment differ among each other, showing the limitations of laboratory calibrations. However, in fields where pore water samples are available, a direct proportionality between pore water EC and sensor bulk EC suffices without correction for VWC in this well irrigated case. Moreover there is a good correlation between the low frequent EC time series of suction cup samples and the high frequent sensor readings. When used with care, sensors can give valuable information about the dynamics of soil conditions during crop salinity tolerance tests.

Comparison of approaches to deal with matrix effects in LC-MS/MS based determinations of mycotoxins in food and feed
Fabregat-Cabello, N. ; Zomer, P. ; Sancho, J.V. ; Roig-Navarro, A.F. ; Mol, H.G.J. - \ 2016
World Mycotoxin Journal 9 (2016)2. - ISSN 1875-0710 - p. 149 - 161.
Calibration - Ion suppression - Isotope dilution mass spectrometry - Matrix effects - Standard addition

This study deals with one of the major concerns in mycotoxin determinations: The matrix effect related to LC-MS/ MS systems with electrospray ionization sources. To this end, in a first approach, the matrix effect has been evaluated in two ways: monitoring the signal of a compound (added to the mobile phase) during the entire chromatographic run, and by classical post-extraction addition. The study was focused on nine selected mycotoxins: Aflatoxin B1, fumonisins B1, B2 and B3, ochratoxin A, deoxynivalenol, T-2 and HT-2 toxins and zearalenone in various sample extracts giving moderate to strong matrix effects (maize, compound feed, straw, spices). Although the permanent monitoring of a compound provided a qualitative way of evaluating the matrix effects at each retention time, we concluded that it was not adequate as a quantitative approach to correct for the matrix effect. Matrix effects measured by post-extraction addition showed that the strongest ion suppression occurred for the spices (up to -89%). Five different calibration approaches to compensate for matrix effects were compared: multi-level external calibration using isotopically labelled internal standards, multi-level and single level standard addition, and two ways of singlepoint internal calibration: one point isotopic internal calibration and isotope pattern deconvolution. In general, recoveries and precision meeting the European Union requirements could be achieved with all approaches, with the exception of the single level standard addition at levels too close to the concentration in the sample. When an isotopically labelled internal standard is not available, single-level standard addition is the most efficient option.

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