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Simulation of the effect of citrate exudation from roots on the plant availability of phosphate adsorbed on goethite
Geelhoed, J.S. ; Riemsdijk, W.H. van; Findenegg, G.R. - \ 1999
European Journal of Soil Science 50 (1999). - ISSN 1351-0754 - p. 379 - 390.
Rhizosphere processes strongly influence the availability of phosphorus (P) to plants. Organic ligands that are exuded from the root surface mobilize phosphorus by dissolution of P minerals or by desorption of adsorbed phosphate. We developed a mechanistic model to study the mobilization of phosphate sorbed on goethite by the exudation of citrate and consequent uptake of phosphate by the root. The use of a model allows the effects of the organic anion and pH on P desorption to be separated. The model is also used to predict concentration profiles developing around the root for phosphate, citrate (with or without accounting for degradation) and pH, providing insight into the processes that occur in the rhizosphere. Results of model calculations show that with larger rates of citrate exudation, greater P availability is predicted. Exudation at a rate of 0.5 mol citrate m1 root day1, which is in the range found for P-deficient plants, increased P availability almost 2-fold at fairly large phosphate loading of goethite (1.9 mol m2) and almost 30-fold at small phosphate loading (1.3 mol m2). Competitive adsorption causes a much greater relative increase in the phosphate concentration in solution at small than at large phosphate loading, which explains this result. Simultaneous acidification of the rhizosphere results in a smaller P mobilization than at a fixed pH of 5, as a result of the pH dependence of phosphate adsorption in the presence of citrate. Sorption of citrate increases its persistence against microbial decay, and hence has a positive effect on the mobilization of adsorbed phosphate.
Phosphate availability in the soil-root system : integration of oxide surface chemistry, transport and uptake
Geelhoed, J.S. - \ 1998
Agricultural University. Promotor(en): G.R. Findenegg; Willem van Riemsdijk. - S.l. : Geelhoed - ISBN 9789054858621 - 177
fosformeststoffen - rizosfeer - voedingsstoffenbeschikbaarheid - oppervlaktechemie - phosphorus fertilizers - rhizosphere - nutrient availability - surface chemistry
<p>A study is presented on the adsorption of phosphate on goethite, the interaction of phosphate with other adsorbing ions at the goethite surface, and the resulting availability of phosphate to plants. The plant-availability of sorbed phosphate was determined from phosphorus uptake of plants growing on an artificial substrate containing goethite with phosphate. Uptake can be predicted from zero sink behaviour of a growing root system, diffusion and mass flow in soil, and measured non linear adsorption of phosphate on goethite. With high phosphate loading of goethite, the equilibrium phosphate concentration in solution increased, which resulted in larger phosphate availability. Competitive interaction between phosphate and sulphate on goethite caused only a small decrease in phosphate adsorption at low pH, where sulphate adsorption is strongest, but a considerable increase in the phosphate concentration in solution.</p><p>Experiments showed that phosphorus uptake by plants growing on suspensions of goethite in the presence of sulphate was seven times larger at pH 3.7 than at pH 5.5. Citrate competes more strongly with phosphate than sulphate, and shows strongest interaction at pH 4.5-5. On account of the non-linear adsorption behaviour of phosphate, the relative increase in phosphate in solution upon competition is much larger at low than at high phosphate loading of goethite. Therefore, competition results in an apparent lower affinity of phosphate sorption on goethite.</p><p>Adsorption of the individual anions and competitive adsorption was described with the CD-MUSIC ion adsorption model, which is based on a detailed description of the adsorbing surface and the use of surface complexes identified in spectroscopic studies. The combination of the ion adsorption model with the uptake model is a powerful tool to predict the phosphate availability to plants. This was illustrated with a simulation study in which the effect of citrate exudation from roots on the uptake of phosphate was predicted.</p>
Potato crop growth as influenced by potato cyst nematodes (Globodera pallida) and abiotic factors
Ruijter, F. de - \ 1998
Agricultural University. Promotor(en): G.R. Findenegg; A.J. Haverkort. - S.l. : De Ruijter - ISBN 9789054858195 - 121
solanum tuberosum - aardappelen - plantenplagen - pratylenchus - heteroderidae - tylenchidae - bodem - nematoda - potatoes - plant pests - soil
<p>The objective of the research described in this thesis was to determine the major mechanisms by which potato cyst nematodes reduce potato crop growth and to explain interactions known to occur with cultivar and abiotic factors. Understanding of these interactions may lead to strategies that potato growers can use to minimise nematode damage.</p><p>The research concentrated on the interaction between nematodes and soil-related factors. Experiments were carried out, mainly under field conditions, in which the effects of varying levels of nematode density, soil compaction, soil pH and phosphorus fertilisation on crop growth of potato cultivars were studied over time. Two methods for studying root growth in the field were compared and special attention was paid to the effects of nematodes on root growth.</p><p>It was found that potato cyst nematodes reduced crop growth at early stages of growth by inducing or aggravating phosphorus deficiency. Compensatory root growth alleviated phosphorus deficiency at later stages of growth. Application of phosphorus fertiliser reduced or prevented nematode-induced phosphorus deficiency, but could not fully prevent nematode damage. Obviously, penetration of nematodes in the roots also impaired crop photosynthesis also through mechanisms other than nutrient deficiency.</p><p>At late stages of growth, nematodes accelerated crop senescence. This was associated with reduced concentrations of nutrients in the foliage, though it seems likely that more mechanisms could be responsible. To resolve this, further study of the senescence of infested crops and options for remedying this is required.</p><p>It was found that tolerance of cultivars to potato cyst nematodes is associated with production of extra roots and large tops, a characteristic of late maturing potato cultivars. The influence of soil parameters on nematode damage was also found to depend on the amount of foliage produced. It is inferred that crops with large tops suffer little yield loss as they are able to maintain ground cover and light interception, even after infestation by potato cyst nematodes.</p><p>It is concluded that farmers can minimise yield loss by choosing tolerant cultivars and by cultural measures. It is suggested that initial nematode-induced phosphorus deficiency can be relieved by fertilisation methods that increase phosphorus in infested plants to adequate levels. Crop senescence may be delayed by increasing nitrogen in infested plants, e.g. by foliar application of a nitrogen fertiliser, but this requires further study.</p>
Effects of sulphate and pH on the plant-availability of phosphate adsorbed on goethite.
Geelhoed, J.S. ; Riemsdijk, W.H. van; Findenegg, G.R. - \ 1997
Plant and Soil 197 (1997). - ISSN 0032-079X - p. 241 - 249.
The adsorption of phosphate on metal (hydr)oxides may be influenced by the pH and by the adsorption of other ions. In this study, the influence of sulphate and pH on phosphate adsorption on goethite and the availability to plants of adsorbed phosphate was examined. Maize plants were grown on suspensions of goethite with adsorbed phosphate, containing the same total amount of phosphate and either 0.11 mM or 2.01 mM sulphate at pH 3.7, 4.6 or 5.5. The uptake of phosphorus by the plants increased with the larger sulphate concentration and decreasing pH. Mean P uptake in the treatment with 2.01 mM sulphate and pH 3.7 was 55 ?mol plant^-1, whereas in the treatment with 0.11 mM sulphate and pH 5.5 it was 2 ?mol plant^-1. Batch adsorption experiments using ^32P and speciation modelling of ion adsorption showed that in the presence of sulphate, the phosphate concentration in solution strongly increased with decreasing pH, due to competitive adsorption between sulphate and phosphate on goethite. Modelled phosphate concentrations in solution in the uptake experiment were all below 0.6 ?M and correlated well with the observed P uptake. This correlation indicates that the strong influence of the sulphate concentration and pH on the plant-availability of adsorbed phosphate results from the competition between sulphate and phosphate for adsorption on goethite.
Modeling zero sink nutrient uptake by roots with root hairs from soil: comparison of two models.
Geelhoed, J.S. ; Mous, S.L.J. ; Findenegg, G.R. - \ 1997
Soil Science 162 (1997). - ISSN 0038-075X - p. 544 - 553.
|Availability to plants of phosphate adsorbed on goethite.
Geelhoed, J.S. ; Findenegg, G.R. ; Riemsdijk, W.H. van - \ 1997
European Journal of Soil Science 48 (1997). - ISSN 1351-0754 - p. 473 - 481.
|Structure, stability and activity of adsorbed enzymes.
Zoungrana, T. ; Findenegg, G.H. ; Norde, W. - \ 1997
Journal of Colloid and Interface Science 190 (1997). - ISSN 0021-9797 - p. 437 - 448.
Transpiration and drought resistance of Douglas-fir seedlings exposed to excess ammonium.
Visser, P.H.B. de; Keltjens, W.G. ; Findenegg, G.R. - \ 1996
Trees-Structure and Function 10 (1996). - ISSN 0931-1890 - p. 301 - 307.
Growth and nutrition of Douglas fir, Scots pine and pedunculate oak in relation to soil acidification
Visser, P.H.B. de - \ 1994
Agricultural University. Promotor(en): N. van Breemen; G.R. Findenegg; W.G. Keltjens. - S.l. : De Visser - ISBN 9789054852902 - 185
bosbouw - houtteelt - bosbouwkundige handelingen - groei - milieufactoren - bomen - bodemchemie - bodemaciditeit - verzuring - beluchting - voedingsstoffenopname (planten) - bodem ph - plantenfysiologie - neerslag - chemische eigenschappen - zuurgraad - zure regen - forestry - silviculture - forestry practices - growth - environmental factors - trees - soil chemistry - soil acidity - acidification - aeration - nutrient uptake - soil ph - plant physiology - precipitation - chemical properties - acidity - acid rain
<p>In a Douglas fir ( <em>Pseudotsuga menziesii</em> (Mirb.) Franco) and in a Scots pine ( <em>Pinus sylvestris</em> L.) stand on sandy soil in the Netherlands, inputs of water, nutrients and acid loads were changed for four years. Effects of soil changes on growth and nutrition were compared with similar foreign experiments, and with some soil-tree relationships in an oak ( <em>Quercus robur</em> L.) stand, which had different soil types within the site. Water limitations in the stands were demonstrated by a 40% to 50% increase in tree basal area growth from water additions of 3 mm d <sup>-1</SUP>or more. Needle N and K contents were depressed and needle shedding was retarded in autumn by irrigation in the Douglas fir stand. In both coniferous stands mineralization and nitrate leaching were enhanced by the moister soil conditions. The modest growth response to nutrient applications in addition to irrigation, proved that no nutrient deficiencies were present at the sites, although foliar P and K increased instantly. The application of dissolved K, Mg and Ca to both acid forest soils increased Al dissolution and decreased Ca/Al ratios in soil solution. This soil reaction was even stronger when applying dissolved (NH <sub>4</sub> ) <sub>2</sub> SO <sub>4</sub> and was explained by the combined effect of soil exchange processes and root uptake of the applied cations, both increasing soil acidification. The applied (NH <sub>4</sub> ) <sub>2</sub> SO <sub>4</sub> initially enhanced tree growth, later followed by growth reduction in the forest stand and tree death in a pot trial at similar NH <sub>4</sub> supply rates.<p>Douglas fir growth was higher at optimal water and nutrient applications when atmospheric loads were excluded. The reduced NH <sub>4</sub> inputs resulted in a decrease of NO <sub>3</sub> leaching, in a lower needle N concentration and tended to decrease Al concentrations and Al/Ca ratios in soil solution relative to the treatment with atmospheric loads.<p>Transpiration of Douglas fir, as measured from sapflow, was drastically reduced during summer drought. Irrigated trees showed optimal transpiration rates and were found to absorb water more readily after rain events relative to previously water-stressed trees. NH <sub>4</sub> applications in a pot trial initially increased shoot growth and transpiration of juvenile Douglas fir, but strong soil acidification later impaired root functioning and water uptake.
|Werkzaamheid van Vegimax in landbouw, tuinbouw en kasteelten.
Findenegg, G.R. ; Struik, P.C. - \ 1994
Wageningen : Unknown Publisher - 10 p.
The effect of phytase on the availability of P from myo-inositol hexaphosphate (phytate) for maize roots.
Findenegg, G.R. ; Nelemans, J.A. - \ 1993
Plant and Soil 154 (1993). - ISSN 0032-079X - p. 189 - 196.
Evaluating the contribution of magnesium deficiency in the aluminium toxicity syndrome in twelve sorghum genotypes.
Tan, K. ; Keltjens, W.G. ; Findenegg, G.R. - \ 1993
Plant and Soil 149 (1993). - ISSN 0032-079X - p. 255 - 261.
Differential distribution of cadmium in lettuce (Lactuca sativa L.) and maize (Zea mays L.)
Florijn, P.J. - \ 1993
Agricultural University. Promotor(en): G.R. Findenegg; M.L. van Beusichem. - Zoetermeer : Florijn - ISBN 9789054851332 - 113
lactuca sativa - slasoorten - zea mays - maïs - plantensamenstelling - cadmium - lettuces - maize - plant composition
<p>Large genotypic variation in shoot Cd concentrations has been reported in literature for several plant species including lettuce ( <em>Lactuca sativa</em> L.) and maize ( <em>Zea mays</em> L.). The objective of this thesis was to elucidate the physiological andlor morphological basis of this differential behaviour using lettuce and maize as test plants.<p>Lettuce varieties were grown on soil and on nutrient solution culture with or without Cd. In contrast to published data, the genotypic variation in Cd uptake and distribution was small. A close similarity in shoot Cd concentrations was obtained, ranging from 8.2 to 10.7 μg Cd g <sup><font size="-2">-1</font></SUP>dry wt. for the soil experiment and from 4. 0 to 8.4 μg Cd g <sup><font size="-2">-1</font></SUP>dry wt. in the water culture. The absorbed Cd was predominantly transported to the shoots. Cadmium had a similar translocation behaviour as calcium. Compared to NO <sub><font size="-2">3</font></sub> -N, NH <sub><font size="-2">4</font></sub> -N nutrition significantly increased the Cd concentrations in shoots and roots at a constant pH of the solution. The Cd partitioning over the plant organs was independent of the form of N nutrition.<p>The variation in shoot Cd concentrations among maize inbred lines was studied in experiments on soil and nutrient solution culture. The Cd concentrations in the shoots ranged from 0.9 to 9.9 μg Cd g <sup><font size="-2">-1</font></SUP>dry wt. for plants grown on Cd-contaminated soil and from 2.5 to 56.9 μg Cd g <sup><font size="-2">-1</font></SUP>dry wt. for the nutrient solution culture. This variation was mainly related to a differential shoot/root partitioning rather than to a differential total uptake. 'Shoot Cd excluders' retained the Cd taken up in the roots, whereas 'non-shoot Cd excluders' exhibited similar Cd concentrations in shoots and roots. This differential Cd distribution pattern persisted in a wide range of environmental conditions such as solution pH or level of Cd supply. Morphological parameters of shoots <em>(e.g.</em> specific leaf area or leaf area ratio) and roots ( <em>e.g.</em> specific root length or specific surface area) were not related to the Cd partitioning.<p>The amount of Cd adsorbed to the roots was about twice as high for 'shoot Cd excluders' compared to 'non-shoot Cd excluders'. The intracellular partitioning of Cd in roots over a 'soluble pool' and an 'insoluble pool' was different in representatives of the two groups of inbreds with similar total root Cd concentrations. Both the amounts of Cd present in the 'soluble pool' and the total amounts of acid-soluble thiol compounds were twice as high for the 'non-shoot Cd excluder' compared to the 'shoot Cd excluder'. Probably the soluble Cd is complexed to metal- binding peptides (phytochelatins) that form part of the acidsoluble thiol compounds. Binding characteristics of Cd to internal structural root components were similar for the two groups of inbreds.<p>It is suggested that the differential Cd distribution between roots and shoots of the maize inbreds is caused by the differential mobility of Cd in their roots, due to the higher amounts of soluble complexes of Cd and acid-soluble thiol compounds in 'non-shoot Cd excluders' compared to 'shoot Cd excluders'.
Analysis of aluminium sensitivity in sorghum (Sorghum bicolor (L.) Moench) genotypes
Tan, K. - \ 1993
Agricultural University. Promotor(en): G.R. Findenegg; W.G. Keltjens. - S.l. : Tan - ISBN 9789054850946 - 155
oogstschade - bodemverontreiniging - bodemgiftigheid - bodemzoutgehalte - Sorghum bicolor - toxische stoffen - chemie - indicatorplanten - toxinen - planten - bodem - aluminium - oogsttoename - oogstverliezen - opbrengsten - zure gronden - kattekleigronden - chemische factoren - crop damage - soil pollution - soil toxicity - soil salinity - toxic substances - chemistry - indicator plants - toxins - plants - soil - yield increases - yield losses - yields - acid soils - acid sulfate soils - chemical factors
<p>Twelve genotypes of sorghum ( <em>Sorghum bicolor</em> (L.) Moench) differing in Al sensitivity were grown in an acid soil (with additions of lime or MgSO <sub>4</sub> ) and in nutrient solutions (with or without Al at constant pH) for periods between 14 and 35 days. The objective was the identification of the factors controlling dry matter yield of sorghum under different growth conditions. In both media Al was the major constraint, restricting growth in two independent ways: (1) by inducing Mg deficiency and (2) via damaging the roots ( <em>i.e.</em> by giving them a stubby and discolorated appearance and by reducing their specific root length, m g <sup>-1</SUP>dry root). The sensitivities of the genotypes against Al-induced Mg deficiency and Al-induced root damage were not correlated. At moderate acidity (pH around 4.8), Mg deficiency dominantly limited growth whilst at a higher acidity (pH ~4.2) root damage overruled Mg deficiency in its negative effect on growth. At pH 4.8, addition of Mg improved growth by reducing the degree of Mg deficiency. At pH 4.2, Mg improved growth mainly by preventing the roots from Al- induced damage.<p>Several external factors modified the AI sensitivity of the genotypes by strengthening or weakening the negative effects of Al on Mg nutrition and root development. At pH 4.2, Ca and NH <sub>4</sub> both counteracted AI-induced root damage but aggravated Al-induced Mg deficiency. The contrary was true for NO <sub>3</sub> . When the concentration of soluble Al was kept approximately constant at 15 μM, both Al-induced root damage and Mg deficiency were aggravated by acidity in the range pH 3.9-4.8. Aluminium toxicity in sorghum grown in nutrient solution was independent of P deficiency, although an increased P supply partly eliminated Al phytotoxicity.<p>The results stress the importance of both Al and Mg ions and their interactions in determining growth response of sorghum and other cereals to acid soils.
|Aluminum toxicity in sorghum genotypes as influenced by solution acidity.
Tan, K. ; Keltjens, W.G. ; Findenegg, G.R. - \ 1993
Soil Science and Plant Nutrition 39 (1993). - ISSN 0038-0768 - p. 291 - 298.
African armyworm outbreaks : why do they occur after drought?
Janssen, J.A.M. - \ 1993
Agricultural University. Promotor(en): L.M. Schoonhoven; G.R. Findenegg. - S.l. : Janssen - ISBN 9789054851196 - 170
insecten - plantenplagen - graansoorten - voedselgewassen - noctuidae - plantenziekten - epidemiologie - distributie - oost-afrika - spodoptera exempta - uitbraken (ziekten) - insects - plant pests - cereals - food crops - plant diseases - epidemiology - distribution - east africa - outbreaks
<p>The African armyworm, <em>Spodoptera exempta</em> (Walker) (Lepidoptera; Noctuidae), feeds almost exclusively on plants of the families Gramineae and Cyperaceae. It is a severe pest of crops, including maize, sorghum and millet, especially on the eastern side of the African continent where a marked seasonal occurrence of outbreaks coincides with the rains. First outbreaks of a season can arise soon after the start of the short rains (October-November) in the so-called primary outbreak areas, which are located in the zone separating the lower desert area to the east from the highlands to the west in Kenya and Tanzania. Adults from these primary outbreaks migrate downwind on the prevailing easterly winds to give rise to subsequent generations further west in secondary outbreak areas. The outbreak season subsequently ends during the long dry season. No further outbreaks are reported, and densities remain very low, until the start of the following short rainy season. Current control aims to destroy, with insecticides, any outbreaks that are critical in terms of their potential to generate upsurges in following generations. Many primary outbreaks are critical in this sense.</p><p>Outbreak development of the African armyworm is known to vary greatly between years in eastern Africa: in some years hardly any outbreaks are reported while in others severe infestations occur over very large areas. Drought (below average precipitation) in particular, has often been associated with the most severe outbreak seasons. As outbreaks usually seem to develop on plants which are free of drought stress but that are growing on soils that have previously been subjected to severe drought for a considerable time, the existence of a delayed indirect effect of drought on outbreak development of the African armyworm is postulated. It is hypothesized that:</p><p><BLOCKQUOTE><em>Periods of more severe drought encourage the occurrence of more severe outbreaks by stimulating the mineralization process in the soil when it is remoistened by rainfall as the drought breaks. This results in higher soil nitrate levels and, consequently, higher nitrogen levels in host plants of the African armyworm, thus increasing larval developmental rate and survival (especially of very young larvae) as well as the fecundity of subsequent adults.</em></BLOCKQUOTE></p><p>This hypothesis is based on the knowledge that the decomposition of organic material by bacteria in a soil after wetting is correlated with the duration and temperature of the drying period to which the soil has been exposed (the socalled 'Birch-effect'), and that higher nitrogen contents in host plants have often been observed to increase herbivore fitness. The aim of the present study has been to test this hypothesis.</p>
Effect of nitrogen form on aluminum toxicity in sorghum genotypes.
Tan, K. ; Keltjens, W.G. ; Findenegg, G.R. - \ 1992
Journal of Plant Nutrition 15 (1992). - ISSN 0190-4167 - p. 1383 - 1394.
|Calcium-induced modification of aluminum toxicity in sorghum genotypes.
Tan, K. ; Keltjens, W.G. ; Findenegg, G.R. - \ 1992
Journal of Plant Nutrition 15 (1992). - ISSN 0190-4167 - p. 1395 - 1405.
Aluminium toxicity with sorghum genotypes in nutrient solutions and its amelioration by magnesium.
Tan, K. ; Keltjens, W.G. ; Findenegg, G.R. - \ 1992
Zeitschrift fur pflanzenernahrung und bodenkunde 155 (1992). - ISSN 0044-3263 - p. 81 - 86.
Acid soil damage in sorghum genotypes: role of magnesium deficiency and root impairment.
Tan, K. ; Keltjens, W.G. ; Findenegg, G.R. - \ 1992
Plant and Soil 139 (1992). - ISSN 0032-079X - p. 149 - 155.