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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    Omgaan met inteelt en verwantschap in de hondenfokkerij
    Bijma, Piter - \ 2015
    Lezing gegeven in Beusichem
    Bouwen aan een betere balans : Een analyse van bedrijfsstijlen in de melkveehouderij
    Dirksen, H. ; Klever, M. ; Broekhuizen, R.E. van; Ploeg, J.D. van der; Oostindië, H.A. - \ 2013
    Beusichem : RSO en DSM - 36 p.
    De mensen van Landbouwscheikunde : een halve eeuw op de Dreijen
    Beusichem, M.L. van; Koenders, K. - \ 2006
    Wageningen : Wageningen Universiteit en Research Centrum, Environmental Sciences Group, Centrum Bodem, Sectie Bodemkwaliteit - 162
    The potentials of multi-nutrient soil extraction with 0.01 M CaCl2 in nutrient management
    Erp, P.J. van - \ 2002
    Wageningen University. Promotor(en): O. Oenema; M.L. van Beusichem. - S.l. : S.n. - ISBN 9789058086648 - 237
    voedingsstoffen - calciumchloride - bodemvruchtbaarheid - bodemchemie - bodemonderzoek - extractie - extraheervloeistoffen - besluitvorming - nutrients - calcium chloride - soil fertility - soil chemistry - soil testing - extraction - extractants - decision making

    Key words: 0.01 M CaCl 2 , soil testing, nutrient management, decision-making, multi-nutrient

    Aim of this thesis is to improve the understanding of nutrient dynamics in soil and thereby to improve decision-making in nutrient management. There is a need for a more mechanistic approach of decision-making because the classical approaches cannot comply with the tightening up of legislation and boundary conditions for sustainable agricultural production.

    The thesis encompasses eight separate papers in which the mechanistic backgrounds of the 0.01 M CaCl 2 soil extraction procedure has been studied as well as the perspectives of the design of a multi-nutrient CaCl 2 soil testing program. The studies have been focussed on the cations Ca, Mg and K. Although the use of CaCl 2 as a soil extractant is promising, it is concluded that the design of a multi-nutrient CaCl 2 soil testing program is time-consuming and costly. A framework for decision-making in nutrient management has been worked out. In this framework the multi-nutrient 0.01 M CaCl 2 soil extraction procedure is used as a standardized procedure to give a chemical characterization of soils at a pH and ionic strength comparable to field conditions. This characterization is used as input in a soil chemical model to calculate nutrient speciation and nutrient distribution under varying conditions. This nutrient speciation and distribution is used to characterize the pool of plant available soil nutrient. It is proposed to integrate the CaCl 2 soil extraction procedure with a soil chemical model, a crop growth model, a soil microbiological, a soil hydraulic model and an optimization procedure into a practical tool for nutrient management decision-making. This tool can then be used i) to tune plant nutrient requirements for maximal crop production and crop quality to the magnitude of the pool of plant available soil nutrient in time and space, and ii) to optimize farm activities in order to comply with more and stricter legislation and boundary conditions related to nutrient management. It is concluded that the perspectives of the multi-nutrient CaCl 2 soil extraction procedure in mechanistic soil nutrient models and in nutrient management are promising.

    Effect of drying temperature on amount of nutrient elements extracted with 0.01 M CaC12 soil extraction procedure
    Erp, P.J. van; Houba, V.J.G. ; Beusichem, M.L. van - \ 2001
    Communications in Soil Science and Plant Analysis 32 (2001). - ISSN 0010-3624 - p. 33 - 48.
    In the current soil drying protocol of the 0.01 M calcium chloride (CaCl2) procedure, soils are oven dried at 40°C for 24 h. At this drying temperature, as well as at lower drying temperatures, a change of the actual soil nutrient element status cannot be excluded because microbes will be active during part of the drying period. However, a higher drying temperature may affect soil characteristics and soil processes and also lead to a misinterpretation of the soil nutrient element status. An explanatory study was conducted to get more insight into the effect of i) oven drying temperature and ii) the use of forced-air ventilation at low drying temperatures on nutrient elements extracted with the 0.01 M CaCl2 procedure. The goal of the study was to investigate the perspectives of optimization of the soil drying protocol of the 0.01 M CaCl2 procedure. Three moist test soils with different soil characteristics were oven dried at 20 and 40°C with and without forced air ventilation and at 70 and 105°C without forced-air ventilation. The moist test soils and the dried soils were extracted with a 0.01 M CaCl2 solution and pH and total N (N), ammonium-nitrogen (NH4-N), nitrate-nitrogen (NO3-N), ortho-phosphate (ortho-P), potassium (K), magnesium (Mg), sodium (Na), and manganese (Mn) determined in the supernatant after centrifugation. Soluble organic N (org-N) was calculated as the difference between N and the summation of NH4-N and NO3-N. In the temperature range from 40 to 105°C, ortho-P, NH4-N, org-N, and Mn extracted tended to increase two or threefold for each 30–35°C increase in drying temperature. Differences in ortho-P, NH4-N, org-N, and Mn extracted at 20 and 40°C were relatively small. The pH, K, Na, and NO3-N extracted were affected by drying temperature but the effect was variable. Magnesium extracted was not affected by drying temperature. The use of forced air ventilation at 20 and 40°C had no significant effect on the amount of org-N, NH4-N, ortho-P, K, and Mg extracted. There were significant effects of forced-air ventilation on pH and NO3-N, Na, and Mn extracted but the effects were variable. Test values (60–70€of the moist test soils were significantly different from the respective test values of the test soils dried at 20 and 40°C with and without forced-air ventilation. Based on the differences between moist and dried soils, it is questionable if soil drying should be recommended in the 0.01 M CaCl2 procedure. Therefore, further research should focus on the relationship between soil test values of moist and dried soils with crop response. If soil drying is preferable drying temperature should not exceed 40°C.
    Actual cation exchange capacity of agricultural soils and its relationship with pH and content of organic carbon and clay
    Erp, P.J. van; Houba, V.J.G. ; Beusichem, M.L. van - \ 2001
    Communications in Soil Science and Plant Analysis 32 (2001). - ISSN 0010-3624 - p. 19 - 31.
    For the set up of a multinutrient 0.01 M calcium chloride (CaCl2) soil testing program a conversion from conventional soil testing programs to a CaCl2 program has been proposed in literature. Such conversion should be based on the relationship between test values of the conventional method and the CaCl2 method. For magnesium (Mg) it was shown in earlier work that the conversion could be improved when the actual cation exchange capacity (CEC) of the soil, CECact, was taken into account. However, determination of CECact necessitates an extra analytical procedure. The goal of this study was to test a procedure for estimating CECact of a soil. In this procedure, CECact was calculated as the summation of the estimated charge of organic carbon (C) and clay in the soil at pHact, the actual pH of the soil. A series of 39 test soils representing agricultural soils in The Netherlands was used to derive the pH dependency of the negative charge of organic C and clay. The following relationship was found: CECact: [M(1)x 0.0624] [M(2)x (0.295-D(2)pHact)]. In this relationship, M(1) and M(2) represent clay and organic C in g kg-1 dry soil, respectively, and D(2)pHact the difference in negative charge of organic C at pHact and pH 8.1. The pHact equals pH measured in 0.01 M CaCl2. The relationship was tested on another dataset of 38 agricultural soils. There was good agreement between the calculated and measured CECact (R2=0.89). It was concluded that the procedure can be used for estimation of CECact.
    Relationship between magnesium extracted by 0.01 M calcium chloride extraction procedure and conventional procedures
    Erp, P.J. van; Houba, V.J.G. ; Reijneveld, J.A. ; Beusichem, M.L. van - \ 2001
    Communications in Soil Science and Plant Analysis 32 (2001). - ISSN 0010-3624 - p. 1 - 18.
    A multinutrient soil extraction procedure in routine soil testing is attractive. Therefore, it has been suggested to convert conventional soil testing programs into a 0.01 M calcium chloride (CaCl2) multinutrient soil testing program using the relationship between test values of the 0.01 M CaCl2 extractant and those of the various conventional extractants. However, these relationships are often weak and an interpretation of the coefficient(s) is almost impossible. Therefore, a fundamental relationship has been deduced relating magnesium (Mg) extracted by conventional methods, (Mg-ext)a, with Mg extracted by the 0.01 M CaCl2 method (Mg-ext)CaCl2: (Mg-ext)a = [* (Mg-ext)CaCl2,t=t] [*(Mg-ext)CaCl2,t=t * (Q-re)CaCl2]. In this relationship, , , and are related to characteristics of the extraction procedure and Mg-fractions in the soils. The (Q-re)CaCl2 is the actual cation exchange capacity of the soil during the CaCl2 extraction. To test the usefulness of this relationship, 39 agricultural soils with widely differing soil characteristics were extracted with 0.01 M CaCl2 and seven conventional Mg extractants. For six conventional methods, the explained variance of the fundamental relationships was more than 0.92. The explained variance of the relationship among 0.01 M CaCl2 and the 0.1 N ammonium-lactate/0.4 N acetic acid extractant buffered at pH 3.75 was poor when the soils contained carbonates. We conclude that the derived fundamental relationship can be used for the design of a CaCl2 soil testing program for Mg. Preferably, this CaCl2 soil testing program should be validated in pot and field experiments.
    Role of nitrifier denitrification in the production of nitrous oxide
    Wrage, N. ; Velthof, G.L. ; Beusichem, M.L. van; Oenema, O. - \ 2001
    Soil Biology and Biochemistry 33 (2001). - ISSN 0038-0717 - p. 1723 - 1732.
    bodemchemie - broeikasgas - milieu - nutriënten - stikstof
    Nitrifier denitrification is the pathway of nitrification in which ammonia (NH3) is oxidized to nitrite (NO2−) followed by the reduction of NO2− to nitric oxide (NO), nitrous oxide (N2O) and molecular nitrogen (N2). The transformations are carried out by autotrophic nitrifiers. Thus, nitrifier denitrification differs from coupled nitrification–denitrification, where denitrifiers reduce NO2− or nitrate (NO3−) that was produced by nitrifiers. Nitrifier denitrification contributes to the development of the greenhouse gas N2O and also causes losses of fertilizer nitrogen in agricultural soils. In this review article, present knowledge about nitrifier denitrification is summarized in order to give an exact definition, to spread awareness of its pathway and controlling factors and to identify areas of research needed to improve global N2O budgets. Due to experimental difficulties and a lack of awareness of nitrifier denitrification, not much is known about this mechanism of N2O production. The few measurements carried out so far attribute up to 30␘f the total N2O production to nitrifier denitrification. Low oxygen conditions coupled with low organic carbon contents of soils favour this pathway as might low pH. As nitrifier denitrification can lead to substantial N2O emissions, there is a need to quantify this pathway in different soils under different conditions. New insights attained through quantification experiments should be used in the improvement of computer models to define sets of conditions that show where and when nitrifier denitrification is a significant source of N2O. This may subsequently render the development of guidelines for low-emission farming practices necessary.
    Effects of salinity on substrate grown vegetables and ornamentals in greenhouse horticulture
    Sonneveld, C. - \ 2000
    Agricultural University. Promotor(en): H. Challa; M.L. van Beusichem. - S.l. : S.n. - ISBN 9789058081902 - 151
    groenten - sierplanten - substraten - zoutgehalte - cultuur zonder grond - glastuinbouw - vegetables - ornamental plants - substrates - salinity - soilless culture - greenhouse horticulture

    Since the mid 1970s substrate growing has become popular in the greenhouse industry in The Netherlands. Because of the small rooting volumes that are used in substrate growing, such systems require an accurate fertilization, but at the same time they offer possibilities for precise control and management of the conditions in the root environment.

    The osmotic potential of the substrate solution in the root environment is often used for improvement of the quality of the produce. For adequate management of the osmotic potential, firstly information about the absorption of water and ions by the crop is essential. Secondly, the effect of the osmotic potential and its interaction with climatic conditions in the greenhouse on crop development must be known. Thirdly, information on the spatial distribution of water and ions in the root environment should be available, because this may strongly affect salinity effects on plants.

    In studies on effects of low osmotic potentials on crops, both osmotic and specific ion effects should be distinguished. The osmotic effects predominate for most crops and growing conditions. Osmotic effects can be described according to the model developed by Maas and Hoffman. This model is characterized by two parameters, the salinity threshold value and the salinity yield decrease value. In this simple model the EC caused by nutrients is not taken into account separately, though nutrients have a significant effect on the EC of the substrate solution in greenhouse cultivation. So the model needs adjustment for the contribution of nutrients to the EC. Furthermore, effects of EC variations in time and space have been described.

    Fruit vegetables and cut flowers were used as test crops in experiments with different EC values in the root environment. Comparisons were made between EC effects caused by NaCl and by nutrients. Yield of tomato, cucumber, and sweet pepper were reduced at increasing EC, but most fruit quality characteristics were favourably affected. Blossom-end rot, however, increased with increasing EC. For sweet pepper this was especially the case after NaCl addition. Salinity threshold values for the vegetable crops varied between 2.3 and 3.5 dS m -1and relative salinity yield decrease values between 2.3 and 7.6 % per dS m -1. The flower weigths of gerbera, carnation, rose, aster, bouvardia and lily were negatively affected by increasing EC. Salinity threshold values ranged from 1.1 to 4.3 dS m -1and salinity yield decrease values varied between 2.1 and 16.8% per dS m -1. For aster such parameters could not be obtained, because the highest EC of 4.2 dS m -1did not affect production. However, the regrowth of this crop after the first harvest was specifically strongly hindered by NaCl. Bouvardia also exhibited a specific sensitivity to NaCl. This effect was studied in more detail to obtain information about which ion, either Na or Cl, was responsible for this effect. The results showed that bouvardia was specifically sensitive to Na.

    The response of tomato and cucumber to an unequal distribution of nutrients and NaCl in the root environment was studied with plants grown in a split-root system. Tomato yield was determined by the EC value considered optimal for production if present in one of the rockwool cubes, despite the fact that the EC in the other cube was up to 10 dS m -1. Tomato absorbed water preferably from the root part with the lowest EC and nutrients from the root part with the highest EC. When the EC in the root parts was raised by nutrients from low to standard values, the nutrient uptake by cucumber was highest from the parts with the highest concentration. In root parts with concentrations of nutrients > 4 dS m -1the uptake decreased strongly. Nutrient uptake from one root part with high NaCl was also reduced when the NaCl concentration in the other part was low. When both root parts had high NaCl concentrations the plant was able to take up adequate amounts of nutrients. Like tomato, cucumber absorbed water preferably from the root part with the lowest EC. In case no nutrients were supplied in one root part, the water uptake from that root part was reduced.

    Interactions between salinity effects and climatic conditions and effects of temporal variation of salinity were studied with tomato as the test crop. High EC under low light conditions did not affect yields. In spring and summer yield reductions between 5 and 7 % per dS m -1were found. In one experiment at very high humidity the yield reduction was about 10 % per dS m -1. This was in contradiction with the nature of the interaction between salinity and climate in other studies. Obviously the calcium status of the plant had played a dominant role in this experiment. From the experiments with temporal variation of EC it could be concluded that for estimation of the yield reduction not only the lengths of the EC-intervals and the EC-level during the interval but also the light intensity during the interval has to be taken into account.

    The management of salinity in relation to nutrient supply was discussed. Nutrient absorption of greenhouse crops was studied by determining the total nutrient uptake and the nutrient uptake in relation to the water absorption (the so-called uptake concentrations). The widely published very low external concentrations to achieve optimal yields, are not realistic because of the high flow rate necessary to adequately supply crops with nutrients. External nutrient concentrations corresponding with 1.5 dS m -1are required for sufficient nutrient supply to greenhouse crops.

    Required and acceptable external concentrations were defined considering the following aspects. Required external concentrations should not exclusively be related to a sufficient supply of nutrients in order to attain maximum growth or yield, but also to quality demands of the market. Acceptable concentrations should be considered with respect to maximum accumulation of residual ions to a level that does not negatively affect crop production and quality. In this way leaching and thus environmental pollution is minimized.

    In the assessment of required and acceptable concentrations osmotic and specific ion effects should be clearly distinguished. When no specific ion effects occur, the "space" between the nutrient concentration required for maximal production and the required concentration with respect to the produce quality or the acceptable concentration with respect to maximum salt accumulation can be filled up with any ion available in the system. With specific ion sensitivities the accumulation is restricted by the critical non toxic level to the crop.

    Required and acceptable concentrations of ions strongly depend on crop and growing conditions. Under cool and humid growing conditions, use of drip irrigation, and CO 2 supply, EC-values in the substrate solution between 3 and 6 dS m -1seem to be realistic. Such conditions can be realised in greenhouses in North-West Europe from autumn until early spring. For summer conditions the EC-values suggested in this study between 1.5 and 3.0 dS m -1are more realistic. In the interpretation of EC-values more credit should be given to the consequences of spatial distribution of ions in the substrate. The stable equilibrium established between low and high concentrated spots in the systems, offers excellent possibilities for an osmotic escape by plants. The discussion is concluded with some calculations of environmental pollution as a consequence of different management strategies of irrigation and drain-off.

    Nitrogen availability and defense of tomato against two-spotted spider mite
    Hoffland, E. ; Dicke, M. ; Tintelen, W. van; Dijkman, H. ; Beusichem, M.L. van - \ 2000
    Journal of Chemical Ecology 26 (2000). - ISSN 0098-0331 - p. 2697 - 2711.
    The aim of this work was to study how nitrogen availability affects within-plant allocation to growth and secondary metabolites and how this allocation affects host selection by herbivores. Tomato plants (Lycopersicon esculentum) were grown at six levels of nitrogen availability. When nitrogen availability increased, plant relative growth rate increased, but tissue carbon/nitrogen ratio in the second oldest true leaf and allocation to large glandular trichomes (type VI) as well as to the defense compounds rutin and chlorogenic acid decreased. Leaf protein concentration increased. Two-spotted spider mite (Tetranychus urticae) females responded significantly to these changes: in dual choice tests they preferred leaf disks from plants grown at high nitrogen availability, with a low C/N ratio. This preference persisted in an olfactometer in which the mites were offered only the odors released by leaves with damaged trichomes. We conclude that in a tomato leaf increased nitrogen availability leads to decreased allocation to defenses, and that repellent volatiles released by trichomes play a key role in affecting leaf selection by two-spotted spider mite females.
    Effect of nitrogen supply rate on disease resistance in tomato depends on the pathogen
    Hoffland, E. ; Jeger, M.J. ; Beusichem, M.L. van - \ 2000
    Plant and Soil 218 (2000). - ISSN 0032-079X - p. 239 - 247.
    The aim of this study was to investigate the effect of tissue nitrogen concentration, as a consequence of nitrogen supply rate, on the susceptibility of tomato plants to three pathogens.We varied tissue N concentration by supplying N at different rates by adding nitrate in different, exponentially increasing amounts to the nutrient solution on which the tomato plants were grown. Separate experiments were carried out to test susceptibility of tomato plants to the bacterial speck-causing Pseudomonas syringae pv tomato, to the wilt agent Fusarium oxysporum f.sp. lycopersici and to tomato powdery mildew caused by Oidium lycopersicum. The effect of tissue N concentration appeared to be highly pathogen-dependent: there was no effect on susceptibility to F. oxysporum, but susceptibility to P. syringae and O. lycopersicum increased significantly with increasing N concentration. We have previously demonstrated the opposite for susceptibility to Botrytis cinerea: decreasing susceptibility with increasing N concentration. The apparent contradictory effects are discussed in relation to the effect of N supply on both the nutritional value of the plant tissue to the pathogen and on the concentration of resistance-related compounds.We conclude that the effect of changing both characteristics on disease susceptibility is highly pathogen-specific and is probably dependent on differences in resource requirements of the pathogen or the sensitivity of the pathogen to plant resistance reactions or on both these factors.
    Effects of nitrogen input and grazing on methane fluxes of extensively and intensively managed grasslands in the Netherlands
    Pol-van Dasselaar, A. van den; Beusichem, M.L. van; Oenema, O. - \ 1999
    Biology and Fertility of Soils 29 (1999)1. - ISSN 0178-2762 - p. 24 - 30.
    Abstract Generally, grasslands are considered as sinks for atmospheric CH4, and N input as a factor which reduces CH4 uptake by soils. We aimed to assess the short- and long-term effects of a wide range of N inputs, and of grazing versus mowing, on net CH4 emissions of grasslands in the Netherlands. These grasslands are mostly intensively managed with a total N input via fertilisation and atmospheric deposition in the range of 300-500 kg N ha-1 year-1. Net CH4 emissions were measured with vented, closed flux chambers at four contrasting sites, which were chosen to represent a range of N inputs. There were no significant effects of grazing versus mowing, stocking density, and withholding N fertilisation for 3-9 years, on net CH4 emissions. When the ground-water level was close to the soil surface, the injection of cattle slurry resulted in a significant net CH4 production. The highest atmospheric CH4 uptake was found at the site with the lowest N input and the lowest ground-water level, with an annual CH4 uptake of 1.1 kg CH4 ha-1 year-1. This is assumed to be the upper limit of CH4 uptake by grasslands in the Netherlands. We conclude that grasslands in the Netherlands are a net sink of CH4, with an estimated CH4 uptake of 0.5 Gg CH4 year-1. At the current rates of total N input, the overall effect of N fertilisation on net CH4 emissions from grasslands is thought to be small or negligible.
    Methane emissions from wet grasslands on peat soil in a nature preserve
    Pol-Van Dasselaar, A. van den; Beusichem, M.L. van; Oenema, O. - \ 1999
    Biogeochemistry 44 (1999). - ISSN 0168-2563 - p. 205 - 220.
    The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH4) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve Nieuwkoopse Plassen, which is a former peat mining and agricultural area. Net CH4 emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH4 emissions was 7.9 g CH4 m- 2 yr-1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH4 m-2 yr-1. The time-course of CH4 emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH4 emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.
    Determinants of spatial variability of methane emissions from wet grasslands on peat soil
    Pol-Van Dasselaar, A. van den; Beusichem, M.L. van; Oenema, O. - \ 1999
    Biogeochemistry 44 (1999). - ISSN 0168-2563 - p. 221 - 237.
    Methane (CH4) emissions from soils, representing the consequence of CH4 production, CH4 consumption and CH4 transport, are poorly characterised and show a large spatial variability. This study aimed to assess the determinants of field-scale spatial variability of CH4 emissions from wet grasslands on peat soil. Mean CH4 emission rates of a three-year experiment at 18 plots distributed over three sites in the nature preserve Nieuwkoopse Plassen on peat soil in the Netherlands were related to CH4 production and CH4 consumption capacities of soil layers, and to soil and vegetation characteristics. Spatial variability of CH4 emissions and possible determining factors was high. Annual CH4 emissions ranged from 3 to 37 g CH4 m-2 yr-1. Coefficients of variation (CV) of CH4 emissions were on average 37% among sites and 83% within sites. Most important determinants of spatial variability were CH4 production capacity (average: 211 ng CH4 g-1 dry soil h-1; CV: 131%) and aboveground biomass of sedges (Carex spp.) (average: 0.45 g dm-2; CV: 127%) (P < 0.01). Sedges may affect CH4 emissions by stimulating CH4 transport from anaerobic layers to the surface via their vascular system and/or by serving as substrate for methanogens. For extrapolation of CH4 emissions to larger areas, best results will be obtained by using factors that are easy to determine, like vegetation.
    Nitrogen availability and susceptibility of tomato leaves to Botrytis cinerea
    Hoffland, E. ; Beusichem, M.L. van; Jeger, M.J. - \ 1999
    Plant and Soil 210 (1999)2. - ISSN 0032-079X - p. 263 - 272.
    The aim of this study was to investigate the effect of nitrogen availability on susceptibility of tomato leaves to the fungal pathogen Botrytis cinerea. Plants with varying nitrogen availability were grown by adding N daily in exponentially increasing amounts to a nutrient solution at different rates. Leaves of plants grown at low nitrogen availability had a high leaf C/N ratio (21 g g-1) and were about 2.5 times more susceptible to primary lesion formation by B. cinerea compared to plant grown at high nitrogen availability, which had a low leaf C/N ratio (11 g g-1). Leaf C/N ratio accounted for 95% of variation in susceptibility. This relationship between C/N ratio and susceptibility persisted when plants were grown with exponential P addition and optimal N supply, and was thus independent of plant growth rate or related factors. We could not explain the effect of nitrogen availability by variation in the most obvious N-based resistance compound α-tomatine because more susceptible leaves with a high C/N ratio contained more α-tomatine. These leaves also contained more soluble carbohydrates. The level of soluble carbohydrates correlated positively with susceptibility, independent of the growth method. We therefore suggest that the effect of N availability on susceptibility must be explained by variation in levels of soluble carbohydrates and speculate about the role of these carbohydrates in the infection process.
    Soil and plant testing programs as a tool for optimizing fertilizer strategies
    Erp, Peter J. van; Beusichem, Marinus L. van - \ 1998
    In: Nutrient Use in Crop Production / Rengel, Z., CRC Press - ISBN 9781560220619 - p. 53 - 80.
    Crop nutrition - Fertilizer recommendations - Plant analysis - Plant testing programs - Soil analysis - Soil testing programs

    Soil and plant testing programs are still based on ‘trial and error’ methods and lack scientific underpinning in terms of relevant soil chemical and plant nutritional processes, and are site-specific. The programs are valuable when the objective is to diagnose and predict deficiencies of plant nutrients. The programs are less valuable for refined fertilizer strategies, like Integrated Nutrient Management, which are e ssential in the near future to satisfy changing agricultural, environmental, economic and legislative boundary conditions. A more scientific approach to soil and plant testing programs appears desirable. To reduce undesirable side-effects o f fertilization on the environment, more emphasis should be placed on fertilizer type and on timing and method of application. [Article copies available for a fee from The Haworth Document Delivery Sendee: 1-800-342-9678. E-mail address: getinfo@haworthpressinc.com].

    Lachgasemissie uit intensief beheerd grasland
    Velthof, G.L. ; Beusichem, M.L. van; Oenema, O. - \ 1998
    Meststoffen : Dutch/English annual on fertilizers and fertilization 98 (1998). - ISSN 0169-2267 - p. 5 - 12.
    melkveehouderij - distikstofmonoxide - modellen - bodemtaxonomie - bodemclassificatie - bodemtypen - dairy farming - nitrous oxide - models - soil taxonomy - soil classification - soil types
    The N2O emission from intensively managed grasslands in the Netherlands, and possible options to mitigate N2O emission, were studied. The study consisted of field studies in which the N2O emission from grassland under different managements was quanti
    Trace elements in crop production
    Beusichem, M.L. van - \ 1998
    Field Crops Research 55 (1998)3. - ISSN 0378-4290 - p. 290 - 291.
    Lachgasemissie uit intensief beheerd grasland.
    Velthof, G.L. ; Beusichem, M.L. van; Oenema, O. - \ 1998
    Meststoffen : Dutch/English annual on fertilizers and fertilization (1998). - ISSN 0169-2267 - p. 5 - 12.
    Mitigation of nitrous oxide emission from dairy farming systems.
    Velthof, G.L. ; Beusichem, M.L. van; Oenema, O. - \ 1998
    In: Nitrogen, the confer-N-s. Eds: Hoek,KW van der; Erisman,JW; Smeulders,S; Wisniewski,JR; Wisniewski,J (1998) Elsevier Science, Amsterdam - p. 173 - 178.
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