Dynamics of dissolved and extractable organic nitrogen upon soil amendment with crop residues
Ros, G.H. ; Hoffland, E. - \ 2010
Soil Biology and Biochemistry 42 (2010)12. - ISSN 0038-0717 - p. 2094 - 2101.
microbial biomass - mineralizable nitrogen - agricultural soils - salt-solutions - forest soils - matter - carbon - n-15 - electroultrafiltration - fractions
Dissolved organic nitrogen (DON) is increasingly recognized as a pivotal pool in the soil nitrogen (N) cycle. Numerous devices and sampling procedures have been used to estimate its size, varying from in situ collection of soil solution to extraction of dried soil with salt solutions. Extractable organic N (EON) not only consists of DON but contains also compounds released from soil biomass and desorbed organic matter. There is no consensus whether DON or EON primarily regulates N mineralisation in soil, and their contribution to N mineralisation has not been quantified simultaneously. We evaluated three sampling procedures on their ability to determine the dynamic of dissolved organic N pools. The three procedures were the determination of DON in 1) soil solution collected by centrifugation, and the determination of EON in 2) a 0.01 M CaCl2 extract of field moist or 3) dried soil. We added unlabeled leek and 15N-labeled ryegrass residues to a loamy sandy soil to create a temporarily increase in DON and EON, to stimulate microbial activity, and to test whether the source and dynamics of the three pools differ. We also tested whether the flow of N through DON or EON was associated with the production of inorganic N using 15N isotope tracing. Sampling procedures significantly affected the amount, but not the dynamics and origin of the three organic N pools. DON and EON (determined on field-moist and dried soils) showed all a significant increase upon crop amendment and returned to their background concentrations within 10 to 30 days. The fraction of DON and EON originating from the crop residue slightly decreased over 138 days and was not different for DON and EON. Field moist extraction of a loamy sandy soil with 0.01 M CaCl2 gave a reliable estimate of the concentration of in situ dissolved organic N. In contrast, extraction of dried soil significantly increased EON compared to DON. The agreement in dynamics, 15N enrichment and C-to-N ratio’s indicate that dissolved and extracted organic N have a similar role in N mineralisation. Our results also suggest that they make a minor contribution to N mineralisation; changes in the turnover rate of EON were not associated with changes in the net N mineralisation rate
Oliebollen in de zomer
Roobeek, K. - \ 2010
Nature Today 2010 (2010)14-07.
bosecologie - rhizina undulata - bedreigde soorten - bosgronden - bodemflora - flora - ecologisch herstel - forest ecology - rhizina undulata - endangered species - forest soils - soil flora - flora - ecological restoration
De oliebolzwam is een typische brandplekpaddenstoel die nu ondanks de grote droogte en hitte bij Schoorl te vinden is. Vroeger algemeen voorkomend als de koffievuurtjeszwam, is het nu in Nederland een bedreigde soort.
Air pollution impacts on European forest soils: steady-state and dynamic modelling
Reinds, G.J. - \ 2009
Wageningen University. Promotor(en): Rik Leemans, co-promotor(en): Wim de Vries; M. Posch. - [S.l.] : S.n. - ISBN 9789085855200 - 223
bodemchemie - bosgronden - ecosystemen - stikstof - europa - luchtverontreiniging - verzuring - zure regen - klimaatverandering - modelleren - soil chemistry - forest soils - ecosystems - nitrogen - europe - air pollution - acidification - acid rain - climatic change - modeling
Zure regen heeft in Europa geleid tot verzuring van bodems en oppervlaktewater. In bosbodems nam de buffercapaciteit af en de bossen werden gevoeliger voor stress als gevolg van, bijvoorbeeld, verstoorde nutriëntenbalansen veroorzaakt door een teveel aan stikstof in de bodem. Deze overmaat aan stikstof veroorzaakte ook veranderingen in natuurlijke vegetaties (meer stikstofminnende soorten). In oppervlaktewater zijn duidelijke schadelijke effecten waargenomen als gevolg van verzuring: in de jaren 70 en 80 trad, vooral in Scandinavië, grote sterfte op onder gevoelige vissoorten. Overmaat aan stiktof leidde lokaal tot eutrofiëring van oppervlaktewater. Kritische depositieniveaus worden meestal berekend met een computermodel dat de bodemverzuring simuleert. Er zijn vele bodemverzuringsmodellen ontwikkeld, maar de meeste daarvan zijn alleen toegepast op puntlocaties en/of regio’s en bovendien zijn de modellen zelden gecalibreerd op grote, regionale datasets. Het doel van dit proefschrift was om (a) na te gaan of beschikbare gegevens uit Europese bosmonitoringsprogramma’s kunnen worden gebruikt om een eenvoudig bodemverzuringsmodel te calibreren (b) op basis van de calibratie na te gaan hoe onzeker de modeluitkomsten zijn en of deze onzekerheid door modelcalibratie afneemt (c) het model toe te passen op Europa en Noord Azië en (d) vast te stellen of de afname van zure depositie leidt to herstel van bodemverzuring in Europa en na te gaan of klimaatverandering daar een invloed op heeft
Effect of temporal resolution on N2O emission inventories in Dutch fen meadows
Nol, L. ; Heuvelink, G.B.M. ; Vries, W. de; Kros, J. ; Moors, E.J. ; Verburg, P.H. - \ 2009
Global Biogeochemical Cycles 23 (2009). - ISSN 0886-6236 - 15
distikstofmonoxide - broeikasgassen - emissie - schattingen - laagveengronden - veenweiden - regen - nederland - nitrous oxide - greenhouse gases - emission - estimates - fen soils - peat grasslands - rain - netherlands - nitrous-oxide emissions - fertilizer application rate - greenhouse-gas emissions - pasture simulation-model - pnet-n-dndc - managed grasslands - field validation - forest soils - nitric-oxide - peat soil
Most countries use a 1-year-resolution emission factor approach (Tier 1 or 2) to estimate terrestrial N2O emissions as part of their national greenhouse gas inventory. Little attention has so far been paid to the effect of the temporal resolution of the approach (e.g., day, season, and year) on N2O emission estimates. The effect of lumping temporal variation can be very large because of daily or seasonal variations of processes causing N2O emissions. Therefore, we compared annual N2O emissions from a model with daily time steps (DNDC) with those of a model with annual time steps (INITIATOR). Emissions were simulated for two intensively managed grassland plots in the Dutch fen meadow landscape. Annual N2O emissions from the investigated grasslands were sensitive to rainfall distribution within the year, especially to summer rainfall. We recommend that Tier 2 N2O emission estimates for intensively managed grasslands on peat soils in the temperate climate zone are adjusted for relative summer rainfall
Habitat type-based bioaccumulation and risk assessment of metal and As contamination in earthworms, beetles and woodlice
Vermeulen, F. ; Brink, N.W. van den; Havé, H. D'; Mubiana, V.K. ; Blust, R. ; Bervoets, L. ; Coen, W. De - \ 2009
Environmental Pollution 157 (2009)11. - ISSN 0269-7491 - p. 3098 - 3105.
hedgehog erinaceus-europaeus - spatial-distribution - forest soils - heavy-metals - trace-metals - accumulation - pollution - spectrometry - floodplain - microwave
The present study investigated the contribution of environmental factors to the accumulation of As, Cd, Cu, Pb and Zn in earthworms, beetles and woodlice, and framed within an exposure assessment of the European hedgehog. Soil and invertebrate samples were collected in three distinct habitat types. Results showed habitat-specific differences in soil and invertebrate metal concentrations and bioaccumulation factors when normalized to soil metal concentration. Further multiple regression analysis showed residual variability (habitat differences) in bioaccumulation that could not be fully explained by differences in soil metal contamination, pH or organic carbon (OC). Therefore, the study demonstrated that in bioaccumulation studies involving terrestrial invertebrates or in risk assessment of metals, it is not sufficient to differentiate habitat types on general soil characteristics such as pH and/or OC alone. Furthermore, simple generic soil risk assessments for Cd and Cu showed that risk characterization was more accurate when performed in a habitat-specific way. Our study provided essential insights into habitat-specific accumulation patterns with respect to factors influencing metal bioaccumulation, BAFs, and site-specific risk assessment
Extractable and dissolved soil organic nitrogen - A quantitative assessment
Ros, G.H. ; Hoffland, E. ; Kessel, C. van; Temminghoff, E.J.M. - \ 2009
Soil Biology and Biochemistry 41 (2009)6. - ISSN 0038-0717 - p. 1029 - 1039.
common arable topsoils - 0.01 m cacl2 - microbial biomass - n-mineralization - norway spruce - agricultural soils - forest soils - sandy soils - seasonal-changes - pastoral soils
Extractable Organic N (EON) or Dissolved Organic Nitrogen (DON) pools are often analyzed to predict N mineralisation, N leaching, and to evaluate agricultural (nutrient) management practices. Size and characteristics of both pools, however, are strongly influenced by methodology. Quantifying the influence of methodology can increase the accuracy of soil tests to predict N mineralisation, improve model simulations, and can help to quantify the contribution of the EON and DON pools to soil N cycling. We estimated the relative impact of methodological, management, and environmental factors on EON and DON, using a meta-analysis approach based on 127 studies. Our results indicate that the EON and DON pools are neither similar in size nor controlled by the same factors. The influence of factors controlling EON generally decreased in the order of methodology (¿10¿2400%), followed by environment (¿11¿270%) and management (¿16¿77%). DON concentrations were primarily controlled by management factors: different land use and fertilisation caused a variation of 37¿118%. Seasonal variations in DON concentrations were generally smaller than variations in EON, suggesting that high mineralisation and sorption rates buffer DON. The large range in EON as affected by different methodology emphasizes the importance of using appropriate and standardized methods for the determination of EON. The determination of DON can be useful to estimate leaching losses. EON, however, can be used to assess the impact of soil management practices on the turnover rate of labile soil organic matter pools
Soil development on Late Quaternary river terraces in a high montane valley in Bhutan, Eastern Himalayas
Tshering Dorji, ; Caspari, T. ; Bäumler, R. ; Veldkamp, A. ; Jongmans, A.G. ; Kado Tshering, ; Tsheten Dorji, ; Baillie, I. - \ 2009
Catena 78 (2009)1. - ISSN 0341-8162 - p. 48 - 59.
forest soils - climate - history - chronosequences - evolution - cations - fungi
We examined the geochemistry and micromorphology of the soils on a suite of morphologically well-defined and visually distinct fluvial terraces, up to 40 m elevation above the current riverbed, at Thangbi in the upper Bumthang Valley, Bhutan. The alluvia forming each of the terraces are lithologically and structurally similar, with shallow or moderately deep, clast-free sandy loam overbank deposits capping deep clast-supported beds of rounded boulders and interstitial sand. The topsoils on the 40 m terrace have more silt than those on the lower terraces. The soils are interpreted mainly as a monoclinal post-incisive chronosequence. Features that indicate progressive pedogenesis with increasing elevation include subsoil rubefaction, crystallinity of free Fe sesquioxides, and weathering of susceptible primary minerals, such as biotite and hornblende. However other soil attributes show no systematic trends and the overall impression is of limited pedogenesis, even in the soils on the higher terraces. We examine possibilities that the immaturity of the soils is due to pedogenic rejuvenation by post-incision additions to the soil parent materials.
The effect of naturally acidified irrigation water on agricultural volcanic soils. The case of Asembagus, Java, Indonesia
Los, A.M.D. ; Vriend, S.P. ; Bergen, M.J. ; Gaans, R.F.M. - \ 2008
Journal of Geochemical Exploration 96 (2008)1. - ISSN 0375-6742 - p. 53 - 68.
mine tailings - forest soils - acidification - netherlands - deposition - aluminum - elements - sulfate - river - iron
Acid water from the Banyuputih river (pH similar to 3.5) is used for the irrigation of agricultural land in the Asembagus coastal area (East Java, Indonesia), with harmful consequences for rice yields. The river water has an unusual composition which is caused by seepage from the acidic Kawah Ijen crater lake into the river. This unique irrigation setting allows the study of soil acidification in situ. This paper assesses the effects of volcanogenically contaminated irrigation water on the chemical properties of the agricultural soils. The changes in soil properties were evaluated by comparing samples taken from the topsoil and sub-soil (1-3 m depth) from areas irrigated with acid water and areas irrigated with neutral water. The field survey thus resulted in four soil categories. Bulk soil composition, organic matter content, moisture content and particle size distribution were determined. Reactive phases were quantified with the selective extractions 1 M KCl, 0.1 M Na-pyrophosphate and 0.2 M acid ammonium oxalate (AAO). By comparing the four soil categories it is shown that the use of the naturally polluted irrigation water has had a large influence on the chemical composition of the topsoil. The composition of the soil solution has changed over the entire investigated soil profile. Furthermore the acid irrigation water has strongly modified the composition of the reactive phases, extracted as KCl, pyrophosphate, and AAO extractable elements, and also the bulk soil composition has been significantly modified. Overall this has resulted in the net dissolution of some elements and the net precipitation of others. The changes in the reactive phases and bulk soil composition are only apparent in the topsoil (0-20 cm) but not in the deeper soil.
Zieke bodem zorgt voor lelijk bos
Kemmers, R.H. - \ 2008
Kennis Online 2008 (2008)nov. - p. 3 - 3.
natuurbescherming - bodem - biologische bodemactiviteit - achteruitgang, bossen - bosecologie - bosgronden - natuur - nature conservation - soil - biological activity in soil - forest decline - forest ecology - forest soils - nature
Op de bosgrond onder de bomen zouden allerhande mossen, bloemen en kruiden moeten kunnen groeien. In Nederland lijdt de kwaliteit van de ondergroei echter al enkele decennia onder verzuring, vermesting en verdroging. Natuurbeheerders doen hun best om de schade te herstellen, maar de genomen maatregelen hebben nog onvoldoende effect. De gewenste planten komen pas terug als de basis goed is: de bodem
Critical loads of metals and other trace elements to terrestrial environments.
Lofts, S. ; Chapman, P. ; Dwyer, R. ; McLaughlin, M. ; Schoeters, I. ; Sheppard, S. ; Adams, W. ; Alloway, B. ; Antunes, P. ; Campbell, P. ; Davies, B. ; Degryse, F. ; Vries, W. de; Groenenberg, J.E. - \ 2007
Environmental Science and Technology 41 (2007)18. - ISSN 0013-936X - p. 6326 - 6331.
forest soils - heavy-metals - cadmium - copper - balances - quality - risk
Effecten van het generieke milieubeleid op het terugdringen van de verzuring en het herstel van natuurwaarden in multifunctionele bossen op arme zandgronden
Kemmers, R.H. ; Dobben, H.F. van; Wamelink, G.W.W. - \ 2007
Wageningen : Alterra (Alterra-rapport 1531) - 83
zandgronden - bosgronden - bosschade - vegetatie - emissie - stikstof - verzuring - herstel - bodembiologie - meervoudig gebruik - bossen - nederland - milieubeleid - ecosystemen - natuurwaarde - sandy soils - forest soils - forest damage - vegetation - emission - nitrogen - acidification - rehabilitation - soil biology - multiple use - forests - netherlands - environmental policy - ecosystems - natural value
Via beschikbare gegevens is geëvalueerd of het generiek milieubeleid sinds 1990 heeft geleid tot terugdringen van de verzuring en vermesting en op herstel van natuurwaarden van Multifunctionele bossen. Als basis voor de evaluatie zijn bodem- en vegetatiegegevens van ca. 200 opstanden uit het meetnet ‘Vitaliteit en Verdroging’ geanalyseerd. Zowel het bodemchemisch als het vegetatiekundig onderzoek bevestigt dat er in multifunctionele bossen sprake is van een licht herstel van de zuurgraad en een daling van ammoniumgehalten. Er is nog steeds sprake van een voortgezette strooiselaccumulatie, waarschijnlijk als gevolg van een weinig actief bodemleven.
Selective depletion of organic matter in mottled podzol horizons
Buurman, P. ; Schellekens, J.F.P. ; Fritze, H. ; Nierop, K.G.J. - \ 2007
Soil Biology and Biochemistry 39 (2007)2. - ISSN 0038-0717 - p. 607 - 621.
chromatography mass-spectrometry - forest soils - chemical characterization - microbial communities - c-13 nmr - pyrolysis - decomposition - acids - biomass - fungi
Some well-drained podzols on quartz sands in the Netherlands and neighbouring Belgium and Germany show mottling in all horizons due to selective removal of organic matter. Phospholipid analysis and morphology of the mottles suggests that this removal is due to a combination of bacteria, fungi, and actinomycetes. Investigation by pyrolysis-GC/MS of organic matter in the depleted zones as compared to their surroundings indicates (1) selective decay of relatively palatable components, (2) residual accumulation of aliphatic biopolymers such as cutan and suberan that produce alkanes, alkenes and methylketones upon pyrolysis, and (3) accumulation of microbial polysaccharides and N-containing compounds. Although the selective organic matter decay in the depleted mottles is similar to the process that causes degradation of organic matter at the top of the B-horizon and its conversion to an E-horizon, the essential difference is that, while decay at the E¿B-horizon transition in podzols is governed by the presence or absence of aluminium and iron, the micro flora that is responsible for the decay mottles acts independently from metal concentrations.
Total soil C and N sequestration in a grassland following 10 years of free air CO2 enrichment
Kessel, C. van; Boots, B. ; Graaff, M.A. de; Harris, D. ; Blum, H. ; Six, J. - \ 2006
Global Change Biology 12 (2006)11. - ISSN 1354-1013 - p. 2187 - 2199.
elevated atmospheric co2 - trifolium-repens l - organic-matter - carbon-dioxide - lolium-perenne - n-15-labeled fertilizer - litter quality - nitrogen pools - forest soils - plant
Soil C sequestration may mitigate rising levels of atmospheric CO2. However, it has yet to be determined whether net soil C sequestration occurs in N-rich grasslands exposed to long-term elevated CO2. This study examined whether N-fertilized grasslands exposed to elevated CO2 sequestered additional C. For 10 years, Lolium perenne, Trifolium repens, and the mixture of L. perenne/T. repens grasslands were exposed to ambient and elevated CO2 concentrations (35 and 60 Pa pCO(2)). The applied CO2 was depleted in delta C-13 and the grasslands received low (140 kg ha(-1)) and high (560 kg ha(-1)) rates of N-15-labeled fertilizer. Annually collected soil samples from the top 10 cm of the grassland soils allowed us to follow the sequestration of new C in the surface soil layer. For the first time, we were able to collect dual-labeled soil samples to a depth of 75 cm after 10 years of elevated CO2 and determine the total amount of new soil C and N sequestered in the whole soil profile. Elevated CO2, N-fertilization rate, and species had no significant effect on total soil C. On average 9.4 Mg new C ha(-1) was sequestered, which corresponds to 26.5% of the total C. The mean residence time of the C present in the 0-10 cm soil depth was calculated at 4.6 +/- 1.5 and 3.1 +/- 1.1 years for L. perenne and T. repens soil, respectively. After 10 years, total soil N and C in the 0-75 cm soil depth was unaffected by CO2 concentration, N-fertilization rate and plant species. The total amount of N-15-fertilizer sequestered in the 0-75 cm soil depth was also unaffected by CO2 concentration, but significantly more N-15 was sequestered in the L. perenne compared with the T. repens swards: 620 vs. 452 kg ha(-1) at the high rate and 234 vs. 133 kg ha(-1) at the low rate of N fertilization. Intermediate values of N-15 recovery were found in the mixture. The fertilizer derived N amounted to 2.8% of total N for the low rate and increased to 8.6% for the high rate of N application. On average, 13.9% of the applied N-15-fertilizer was recovered in the 0-75 cm soil depth in soil organic matter in the L. perenne sward, whereas 8.8% was recovered under the T. repens swards, indicating that the N-2-fixing T. repens system was less effective in sequestering applied N than the non-N-2-fixing L. perenne system. Prolonged elevated CO2 did not lead to an increase in whole soil profile C and N in these fertilized pastures. The potential use of fertilized and regular cut pastures as a net soil C sink under long-term elevated CO2 appears to be limited and will likely not significantly contribute to the mitigation of anthropogenic C emissions.
Effect of land use on the composition of soil organic matter in density and aggregate fractions as revealed by solid-state 13C NMR spectroscopy
Helfrich, M. ; Ludwig, B. ; Buurman, P. ; Flessa, H. - \ 2006
Geoderma 136 (2006)1-2. - ISSN 0016-7061 - p. 331 - 341.
chemical-composition - humic substances - forest soils - carbon - cultivation - residues - dynamics - plant - cpmas
Changes in soil organic carbon (SOC) contents with soil cultivation have been investigated extensively, but information on the influence of land use changes on the chemistry of soil organic matter (SOM) and SOM fractions is scarce. To make a contribution in this context, we sampled silty soils under different land use (spruce forest (Ah horizon, 0-7 cm), continuous maize cropping (Ap horizon, 0¿30 cm), and grassland (Ah horizon, 0-10 cm)) as well as the organic layer (L, Of, and Oh) of the forest floor and collected plant materials from the three sites. Separation of SOM density fractions (free particulate organic matter, occluded particulate organic matter, and mineral-associated organic matter) and water-stable aggregate size fractions of the surface soils was performed in order to follow changes in the chemical composition of SOM in physical soil fractions using CPMAS 13C NMR spectroscopy and to determine land use effects on the chemistry of SOM fractions. The CPMAS 13C NMR spectra showed that maize litter had the highest content of O-alkyl-C and the lowest content of alkyl-C, aryl-C and carbonyl-C compared with the plant material from the spruce stand and the grassland. The forest litter had the largest content of aromatic and alkyl-C. Decomposition of spruce litter in the humus layer resulted in a decreasing O-alkyl-C content and an increasing alkyl-C content. The SOM of the acid forest soil consisted mainly of particulate organic matter (POM) with a high content of spruce litter-derived alkyl-C. The SOC stocks in the grassland and maize soil were dominated by mineral-associated SOM which contained relatively larger proportions of aryl and carbonyl-C. The decrease of the SOC concentration induced by cultivation resulted in a relative accumulation of aromatic C structures in the mineral-bound SOM. In all soils, the free POM had a smaller proportion of alkyl-C and a larger proportion of O-alkyl-C than the POM occluded in aggregates. The mean age of the SOM in the density fractions of the maize soil increased with increasing aromaticity in the order free POM
Fungal/bacterial ratios in grassland with contrasting nitrogen management
Vries, F.T. de; Hoffland, E. ; Eekeren, N.J.M. van; Brussaard, L. ; Bloem, J. - \ 2006
Soil Biology and Biochemistry 38 (2006)8. - ISSN 0038-0717 - p. 2092 - 2103.
soil microbial communities - clover trifolium-repens - arbuscular mycorrhizal fungi - bacterial biomass ratios - ryegrass lolium-perenne - white clover - organic-matter - upland grassland - forest soils - leucine incorporation
It is frequently hypothesised that high soil fungal/bacterial ratios are indicative for more sustainable agricultural systems. Increased F / B ratios have been reported in extensively managed grasslands. To determine the shifts in fungal/bacterial biomass ratio as influenced by grassland management and to find relations with nitrogen leaching potential, we sampled a two-year-old field experiment at an organic experimental farm in the eastern part of The Netherlands. The effect of crop (grass and grass-clover), N application rate (0, 40, 80, 120 kg N ha- 1) and manure type (no manure, farm yard manure and slurry) on the F / B ratio within three growing seasons was tested, as well as relations with soil and crop characteristics, nitrate leaching and partial N balance. Biomass of fungi and bacteria was calculated after direct counts using epifluorescence microscopy. Fungal and bacterial biomass and the F / B ratio were higher in grass than in grass-clover. The F / B ratio decreased with increasing N application rate and multiple regression analysis revealed a negative relationship with pH. Bacterial activity (measured as incorporation of [3H]thymidine and [14C]leucine into bacterial DNA and proteins) showed the exact opposite: an increase with N application rate and pH. Leaching increased with N application rate and was higher in grass-clover than in grass. Partial N balance was more positive at a higher N application rate and showed an inverse relationship with fungal biomass and F / B ratio. We conclude that the fungal/bacterial biomass ratio quickly responded to changes in management. Grasslands with higher N input showed lower F / B ratios. Grass-clover had a smaller fungal biomass and higher N leaching than grass. In general, a higher fungal biomass indicated a lower nitrogen leaching and a more negative partial N balance (or smaller N surplus), but more observations are needed to confirm the relationship between F / B ratio and sustainability.
Simplified denitrification models: overview and properties
Heinen, M. - \ 2006
Geoderma 133 (2006)3-4. - ISSN 0016-7061 - p. 444 - 463.
nitrous-oxide evolution - management model - winter-wheat - forest soils - potential denitrification - generalized-model - rainfall events - empirical-model - water-quality - n2o emissions
This paper reviews simplified process models for denitrification. More than fifty models were considered. The majority of these (simple) models are based on potential denitrification-either measured as a soil's property or computed from organic C dynamics-or consider denittification as a first-order decay process. As it is generally accepted that environmental soil conditions affect the denitrification process, reduction functions are used. Although denitrification is truly driven by the non-availability of oxygen, most authors argue that oxygen dynamics in soil is hard to simulate (or to measure). Therefore, water content is used as a complementary for oxygen diffusion. The higher the water content, the less oxygen will be present. Other factors that influence denitrification are nitrate-nitrogen content, soil temperature and soil acidity (pH). The availability of easily decomposable organic carbon determines the value of potential denitrification or the first-order decay rate constant. Although there seems to be consensus about the mathematical formulation of the simple process model, the shapes of the reduction functions differ largely between the models, especially for the water content reduction function. From a sensitivity analysis it follows that the model is most sensitive to the parameters of the water content reduction function, indicating that these parameters and the water content must be determined with great accuracy.
Effect of ectomycorrhizal fungi on the uptake of Ca, Mg and Al by Pinus sylvestris under aluminium toxicity
Schöll, L. van; Keltjens, W.G. ; Hoffland, E. ; Breemen, N. van - \ 2005
Forest Ecology and Management 215 (2005)1-3. - ISSN 0378-1127 - p. 352 - 360.
norway spruce seedlings - fungus suillus-variegatus - picea-abies seedlings - paxillus-involutus - mineral-nutrition - rigida seedlings - nutrient-uptake - critical loads - organic-acids - forest soils
Aluminium toxicity has been considered an important factor in forest decline. In earlier pot experiments, ectomycorrhizal tree seedlings were reported to have higher growth rates than non-mycorrhizal seedlings under aluminium toxicity. In this paper, we test that if this is caused by exclusion of Al and higher uptake of Ca and Mg by the ectomycorrhizal roots. Pinus sylvestris seedlings, grown for 3 months on a semi-hydroponic system, were continuously drip-irrigated with nutrient solution, containing 0 or 1.5 mM Al. The seedlings were non-mycorrhizal or colonized by ectomycorrhizal fungal species from a podzol soil. The presence of 1.5 mM Al in solution significantly decreased the dry weights of needles and roots compared to the control, and increased mycorrhizal colonization. Yet growth was not affected by mycorrhizal colonization. Concentrations of Al in the needles were significantly higher at 1.5 mM Al in solution than at 0 mM Al, and significantly higher in ectomycorrhizal seedlings than in non-mycorrhizal seedlings. Concentrations of Ca and Mg in the needles were significantly lower at 1.5 mM Al in solution than at 0 mM Al, but were not affected by ectomycorrhizal colonization. In conclusion, ectomycorrhizal colonization did not mitigate aluminium toxicity in our semi-hydroponic system. We suggest that better growth of soil-grown ectomycorrhizal tree seedlings compared to non-mycorrhizal tree seedlings should be explained by improved uptake of immobile nutrients such as P through a better soil exploration by the external mycelium or by detoxification of Al by organic anions excreted by the fungi
Podzolisation and soil organic matter dynamics
Buurman, P. ; Jongmans, A.G. - \ 2005
Geoderma 125 (2005)1-2. - ISSN 0016-7061 - p. 71 - 83.
methylation-mass spectrometry - podzol formation - southern queensland - chemical properties - size fractions - forest soils - bh horizons - aluminum - carbon - podzolization
Present models of podzolisation emphasize the mobilization and precipitation of dissolved organic matter. together with Al(-silicates) and Fe. Such models cannot explain the dominance of pellet-like organic matter in most boreal podzols and in well-drained podzols outside the boreal zone, and the discrepancy between the chemistry of percolating organic matter (DOC) and the organic matter accumulated in well-drained podzol-B horizons. The present paper offers an amended podzolisation theory, in which relative contribution of illuviated organic matter and root litter together with organic matter dynamics provide an explanation for the large variation in podzol morphology, It is suggested that fast organic matter dynamics as occurs on nutrient-rich parent materials in the boreal zone causes small accumulation of organic matter, mainly derived from roots. In such soils. the colors of Fe components dominate in the B horizon. Slow organic matter dynamics, as occurs on nutrient-poor parent materials and under hydromorphic circumstances, favors large organic matter accumulations in the B horizon. and a larger abundance of DOC-derived organic matter coatings. The latter group includes tropical podzols. (C) 2004 Elsevier B.V. All rights reserved.
Decomposition of 14C-labeled roots in a pasture soil exposed to 10 years of elevated CO2
Groenigen, C.J. van; Gorissen, A. ; Six, J. ; Harris, D. ; Kuikman, P.J. ; Groenigen, J.W. van; Kessel, C. van - \ 2005
Soil Biology and Biochemistry 37 (2005)3. - ISSN 0038-0717 - p. 497 - 506.
atmospheric carbon-dioxide - organic-matter dynamics - trifolium-repens l - microbial biomass - lolium-perenne - forest soils - tallgrass prairie - litter quality - fine roots - turnover
The net flux of soil C is determined by the balance between soil C input and microbial decomposition, both of which might be altered under prolonged elevated atmospheric CO2. In this study, we determined the effect of elevated CO2 on decomposition of grass root material (Lolium perenne L.). 14C-labeled root material, produced under ambient (35 Pa pCO2) or elevated CO2 (70 Pa pCO2) was incubated in soil for 64 days. The soils were taken from a pasture ecosystem which had been exposed to ambient (35 Pa pCO2) or elevated CO2 (60 Pa pCO2) under FACE-conditions for 10 years and two fertilizer N rates: 140 and 560 kg N ha¿1 year¿1. In soil exposed to elevated CO2, decomposition rates of root material grown at either ambient or elevated CO2 were always lower than in the control soil exposed to ambient CO2, demonstrating a change in microbial activity. In the soil that received the high rate of N fertilizer, decomposition of root material grown at elevated CO2 decreased by approximately 17% after incubation for 64 days compared to root material grown at ambient CO2. The amount of 14CO2 respired per amount of 14C incorporated in the microbial biomass (q14CO2) was significantly lower when roots were grown under high CO2 compared to roots grown under low CO2. We hypothesize that this decrease is the result of a shift in the microbial community, causing an increase in metabolic efficiency. Soils exposed to elevated CO2 tended to respire more native SOC, both with and without the addition of the root material, probably resulting from a higher C supply to the soil during the 10 years of treatment with elevated CO2. The results show the importance of using soils adapted to elevated CO2 in studies of decomposition of roots grown under elevated CO2. Our results further suggest that negative priming effects may obscure CO2 data in incubation experiments with unlabeled substrates. From the results obtained, we conclude that a slower turnover of root material grown in an `elevated-CO2 world¿ may result in a limited net increase in C storage in ryegrass swards.
Mapping coastal vegetation using an expert system and hyperspectral imagery
Schmidt, K.S. ; Skidmore, A.K. ; Kloosterman, E.H. ; Oosten, H. van; Kumar, L. ; Janssen, J.A.M. - \ 2004
Photogrammetric Engineering and Remote Sensing 70 (2004)6. - ISSN 0099-1112 - p. 703 - 715.
forest soils - salt-marshes - gis
Mapping and monitoring salt marshes in the Netherlands are important activities of the Ministry of Public Works (Rijkswaterstaat). The Survey Department (Meetkundige Dienst) produces vegetation maps using aerial photographs. However, it is a time-consuming and expensive activity. The accuracy of the conventional vegetation map derived using aerial photograph interpretation (API) is estimated to be approximately 43%. An alternative method is demonstrated that uses an expert system to combine airborne hyperspectral imagery with terrain data derived from radar altimetry. The accuracy of the vegetation map generated by the expert system increased to 66%. When hyperspectral imagery alone was used to classify coastal wetlands, an accuracy of 40% was achieved - comparable to the accuracy of the API-derived vegetation map. An analysis of the efficiency of the proposed expert system showed that the speed of map production is increased by using the new method. This means that digital image classification using the expert system is an objective and repeatable method superior to the conventional API method.