bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nutrient concentrations and acidity in ferralitic soil under perennial cropping, fallow and primary forest in central Amazonia
Authors: Schroth G. , Seixas R. , Da Silva L. F. , Teixeira W. G. , Zech W. 
Published: March 2003

SummaryThe long‐term productivity on the acidic, nutrient‐poor upland soils of central Amazonia depends to a large extent on the chemical soil fertility as influenced by vegetation type and management. We compared soil and soil solution data from permanent cropping, fallow and primary forest on a Xanthic Ferralsol in central Amazonia to evaluate changes of soil fertility following forest conversion, agricultural use at different intensities and setting aside agricultural land. The agricultural systems included a perennial polyculture at two fertilizer inputs and a monoculture plantation. Soil and soil solution were collected to 2 m depth, and the soil solution was monitored over 2 years. Both soil and soil solution data showed decreasing soil fertility in the sequence: monoculture and polyculture at large input, polyculture at small input, forest and fallow. The soil solution data were more sensitive to effects of systems and fertilizer inputs on subsoil fertility. Fractionation of the N in the soil solution showed a larger proportion of dissolved organic N in the N‐poor fallow soil than in the soil under forest and agriculture. The soil under fallow, forest and low‐input agriculture had larger exchangeable acidity than that under high‐input agriculture, but the Al concentrations in the soil solution were very small because there were few cations with which to exchange and less nitrification. In high‐input agriculture, pronounced acidification peaks in the topsoil solution followed fertilization. The comparison of soil and soil solution data explained why the spontaneous vegetation thrives at very large exchangeable acidity in these soils, whereas agricultural systems often depend on liming to reduce the concentration of toxic Al in the soil.
Characterization of β‐d‐glucosidase extracted from soil fractions
Authors: Busto M. D. , Perez‐Mateos M. 
Published: March 2003

SummaryOne way to study the state in which stabilized extracellular enzymes persist and are active in the soil is by extraction from the soil, with subsequent fractionation of enzyme–organomineral complexes and characterization of such complexes. In order to investigate the location and characteristics of soil β‐glucosidase, three soil fractions were obtained both from real (undisturbed) soil aggregates and from structural (dispersed in water and physically disrupted) aggregates using two different granulometric procedures. The β‐glucosidase activity of the fraction was then assayed. When the aggregates were dispersed, more than 73% of activity was in the soil microaggregates with diameters of less than 50 μm (SF50). These aggregates were associated with strongly humified organic matter. Solutions of diluted pyrophosphate at neutral pH liberated active β‐glucosidase from all fractions, although the efficacy of extraction varied according to the type of fraction. The SF50fraction and aggregates of 2000–100 μm obtained by sieving (SF2000) showed the greatest β‐glucosidase activity (34.5 and 36.0%, respectively). Micro‐ and ultrafiltration of SF50extracts increased the total β‐glucosidase activity, whereas these procedures, applied to the RF2000fraction, decreased it. Humus–β‐glucosidase complexes in the SF50fraction, between 0.45 μm and 105nominal molecular weight limit (nmwl) (SF50II) and < 105nmwl(SF50III) showed an optimum pH at 5.4, and in the SF50I fraction (> 0.45 μm) the optimum was 4.0. The stability of β‐glucosidase in the aggregates of the smallest size SF50II and SF50III decreased at acid pHs. The presence of two enzymes (or two forms of the same enzyme) catalysing the same reaction with different values of Michaelis constant and maximum velocity was observed in all but one of the β‐glucosidase complexes extracted and partially purified from the SF50aggregates.
The effect of aging biosolids on the availability of cadmium and zinc in soil
Authors: Stacey S. , Merrington G. , McLaughlin M. J. 
Published: March 2003

SummaryA major concern with the safe re‐use of biosolids on land is the potential for release of metals from organic matter in the biosolids, due to decomposition proceeding as biosolids age. To quantify the effects of biosolid aging on Cd and Zn bioavailability, two sewage sludges (Lagoon sludge and Filtered sludge) and a garden compost were incubated at 25°C and 35°C for 100 days. Changes in availability of Cd and Zn were determined using isotope dilution principles, with the materials being labelled with carrier‐free 109Cd and 65Zn. We determined isotopically exchangeable metal pools (E values) and plant available metal pools (L values) by measuring specific activities of Cd and Zn in soil extracts and in wheat plants, respectively. Changes in carbon content over time were determined using 13C‐NMR spectroscopy and chemical extraction methods, and related to changes in availability of metal pools as determined by isotopic procedures.Hot‐water‐extractable carbon content, assumed to represent easily decomposable organic matter, decreased during the 100 days by 80–190 mg kg−1. The Compost and Lagoon sludge showed no change in L values for Cd or Zn with time, but in the Filtered sludge the L values for Cd and Zn increased significantly, by 43% and 56%, respectively. The isotopically exchangeable pools of Cd and Zn did not change with incubation treatment of the biosolids.These data indicate that the potential for metal release from biosolids as organic matter decomposes depends to a large extent on the biosolid composition.
Influence of the rhizosphere on microbial biomass and recently formed organic matter
Authors: De Neergaard A. , Magid J. 
Published: March 2003

SummaryWe have aimed to quantify the effect of roots on the size of the soil microbial biomass, and their influence on the turnover of soil organic matter and on the extent of the rhizosphere. We sampled a sandy clay loam topsoil from two subplots with different treatment histories. One had a normal arable fertilization record, the other had received only inorganic nitrogen fertilizer but no phosphorus and potassium for 30 years.Glucose labelled with14C was added to both samples which were then incubated for 4 weeks before the soil was packed in cylinders and planted with ryegrass. In both soils, microbial biomass at the root surface doubled during the first 8 days. At day 15, the microbial biomass had further increased in the fertile soil, and the rhizosphere effect had extended 2.5 mm into the fertile soil, but to only 1 mm in the infertile soil.The microbial14C increased threefold near the roots in the fertile soil as a result of assimilation of previously formed microbial residues, but in the infertile soil there was no increase. There was a close relation between the increase in microbial14C and a decrease in14C soluble in 2 mKCl, indicating that the microbial residues were more weakly adsorbed in the fertile soil. We conclude that the increased microbial population living near the root surfaces re‐assimilated part of the14C‐labelled microbial residues in the fertile soil. In the infertile soil, microbial residues resisted decomposition because they were more strongly sorbed on to soil surfaces.
The effects of temperature, water‐filled pore space and land use on N2O emissions from an imperfectly drained gleysol
Authors: Dobbie K. E. , Smith K. A. 
Published: March 2003

SummaryTo investigate the effect of soil physical conditions and land use on emissions of nitrous oxide (N2O) to the atmosphere, soil cores of an imperfectly drained gleysol were taken from adjacent fields under perennial ryegrass and winter wheat. The cores were fertilized with ammonium nitrate and incubated at three different temperatures and water‐filled pore space (WFPS) values, and N2O emissions were measured by gas chromatography. Emissions showed a very large response to temperature. Apparent values of Q10 (emission rate at (T + 10)°C/emission rate at T°C) for the arable soil were about 50 for the 5–12°C interval and 8.9 for 12–18°C; the corresponding Q10s for the grassland soil were 3.7 and 2.3. Emissions from the grassland soil were always greater than those from the arable soil, although the ratio narrowed with increasing temperature. Changes in soil WFPS also had a profound effect on emissions. Those from the arable soil increased about 30‐fold as the WFPS increased from 60 to 80%, while that from the grassland soil increased 12‐fold. This latter response was similar to earlier field measurements. The N2O emissions were considered to be produced primarily by denitrification. We concluded that the impacts of temperature and WFPS on emissions could both be explained on the basis of existing models relating increasing respiration or decreased oxygen diffusivity, or both, to the development of anaerobic zones within the soil.
Retention and release of dissolved organic matter in Podzol B horizons
Authors: Zysset M. , Berggren D. 
Published: March 2003

SummaryThe main objectives were to study the effects of pH on the retention and release of organic matter in acid soil, and to determine the main differences in results obtained from batch experiments and experiments in columns. We took soil material from the B horizons of a Podzol at Skånes Värsjö (southern Sweden). In batch experiments, soil was equilibrated with solutions varying in pH and concentration of dissolved organic C. In Bh samples, the release of dissolved C gradually increased with increase in pH. In the Bs1 material there was a minimum at pH 4.1, and in the Bs2 soil the minimum occurred at pH 4.6. The ability to retain added dissolved C increased in the order Bh < Bs1 < Bs2.The column experiment was run for 160 days under unsaturated flow conditions. Columns were packed with Bh, Bh + Bs1 or Bh + Bs1 + Bs2 samples to calculate mass balances for each horizon. Solutions either without any dissolved organic C or ones containing 49 mg C dm−3 with pH of 4.0 or 3.6 were used to leach columns. The pH of input solutions only little affected the concentration of dissolved C in the effluent. Relative proportions of hydrophobic substances decreased with increasing column length and decreasing pH. For input solutions containing dissolved C, near steady state was achieved for both the Bs1 and Bs2 horizons with approximately 25% dissolved organic matter retention. Thus, no maximum sorption capacity for dissolved C could be defined for these horizons. This behaviour could not have been predicted by batch data, showing that column experiments provide useful additional information on interactions between organic compounds and solid soil material.
The impact of long‐term cultivation and management history on the status and dynamics of cobalt in a savanna Alfisol in Nigeria
Authors: Agbenin J. O. 
Published: March 2003

SummaryThe status of cobalt (Co) in savanna soils of Nigeria is largely unknown, and a long‐term experiment including inorganic fertilizer (NPK) and farmyard manure (FYM) and uncultivated land provided information on the way management affected the dynamics of Co in the soil. Total Co increased with increasing depth, whereas readily extractable Co decreased. The mean concentration of Co (5.6–7.9 mg kg−1) was close to the mean value of 8 mg kg−1reported for soils worldwide, whereas the concentration of extractable Co was less than that reported in most soils. Regression analysis indicated that total Fe predicted up to 78% of the soil Co. The potentially available Co correlated strongly with pedogenic or reducible Mn oxides extracted with dithionite–citrate–bicarbonate. Mass balance calculations showed that fertilization with either NPK or FYM caused losses of between 0.8 and 1.1 g Co m−2after 50 years of cultivation against the uncultivated site as a reference. However, Co increased by 1.8 g m−2in the soil receiving FYM + NPK, suggesting that the Co of the soil was best maintained under this management probably because of incidental additions of Co in the manures. Furthermore, the positive Co balance in the FYM + NPK plot was partly enhanced by its larger contents of clay, Fe and pedogenic Mn oxides than in either the FYM or NPK plots. Clay, Fe and pedogenic oxides served as Co sinks in this particular savanna soil.
Generalized linear models in soil science
Authors: Lane P. W. 
Published: March 2003

SummaryClassical linear models are easy to understand and fit. However, when assumptions are not met, violence should not be used on the data to force them into the linear mould. Transformation of variables may allow successful linear modelling, but it affects several aspects of the model simultaneously. In particular, it can interfere with the scientific interpretation of the model. Generalized linear models are a wider class, and they retain the concept of additive explanatory effects. They provide generalizations of the distributional assumptions of the response variable, while at the same time allowing a transformed scale on which the explanatory effects combine. These models can be fitted reliably with standard software, and the analysis is readily interpreted in an analogous way to that of linear models. Many further generalizations to the generalized linear model have been proposed, extending them to deal with smooth effects, non‐linear parameters, and extra components of variation. Though the extra complexity of generalized linear models gives rise to some additional difficulties in analysis, these difficulties are outweighed by the flexibility of the models and ease of interpretation. The generalizations allow the intuitively more appealing approach to analysis of adjusting the model rather than adjusting the data.
Cation exchange properties of acid forest soils of the northeastern USA
Authors: Johnson C. E. 
Published: March 2003

SummaryNegative correlations between soil pH and cation exchange capacity (CEC) or base saturation in soils of the northeastern USA and Scandinavia have raised questions regarding the nature of cation exchange in acid forest soils. Using data from three small‐catchment studies and an extensive regional survey of soils in the northeastern USA, I examined relationships among total carbon, effective CEC (CECe), soil pHs(in 0.01 mCaCl2) and base saturation. Organic matter is the predominant source of soil surface charge in these coarse‐grained, glacially derived soils. Correlation coefficients (r) between total carbon and CECeranged from 0.43 to 0.74 in organic horizons and from 0.46 to 0.83 in mineral horizons. In all cases, the intercepts of functional relations between CECeand total C were near zero. In O horizons, the CECeper unit mass of organic carbon (CECe:C) was positively correlated with pHsin three of the four data sets, consistent with the weak‐acid behaviour of the organic matter. However, CECe:C was negatively correlated with pHsin mineral soils in two data sets, and uncorrelated in the other two. The CECein mineral soils represents the portion of total CEC not occupied by organically bound Al. The negative correlations between CECe:C and pHscan therefore be explained by increased Al binding at higher pHs. Aluminium behaves like a base cation in these soils. When Al was considered a base cation, the relation between base saturation and pHscould be effectively modelled by the extended Henderson–Hasselbalch equation. When modelled without Al as a base cation, however, there were no consistent relationships between pHsand base saturation across sites or soil horizons. Because of the non‐acidic behaviour of Al, it is difficult to predict the effect of ongoing reductions in acid deposition on the base status of soils in the northeastern USA.
Interpretation of humic acid coagulation and soluble soil organic matter using a calculated electrostatic potential
Authors: Weng L. , Temminghoff E. J.M. , Van Riemsdijk W. H. 
Published: March 2003

SummaryThe coagulation of humic substances and its role in controlling the solubility of organic matter in soils are not well understood. We therefore studied the physico‐chemical behaviour of purified humic acid from forest soil coagulated with Na, Ca, Cu, Al at pH 4 and 6, and then modelled the behaviour with the Non‐Ideal Consistent Competitive Adsorption Donnan (NICA‐Donnan) model. We found that the coagulation of humic acid occurs when the Donnan potential is less negative than −0.08 V. Based on this result, an empirical relation between the Donnan potential of humic acid and its concentration in solution was derived. In addition, the Donnan potential of the dissolved organic matter in the soil solution of six soil profiles from forests was calculated using the NICA‐Donnan model under the assumption that all the dissolved organic matter behaves as humic acid. The measured concentration of dissolved organic matter also decreases in a soil profile, as the calculated potential becomes less negative. The results are in many cases in semi‐quantitative agreement with the predicted concentration based on the humic acid coagulation experiment. Acid soils contain more dissolved organic matter, which may result from the presence of a fairly large fraction of more soluble organic molecules, such as fulvic acid.
Modelling the turnover of 15N‐labelled fertilizer and cover crop in soil and its recovery by maize
Authors: Hadas A. , Doane T. A. , Kramer A. W. , Van Kessel C. , Horwath W. R. 
Published: March 2003

SummaryThe rate at which available nitrogen (N) is released from organic materials in soil is often measured by applying 15N and following its recovery by the growing crop. However, the turnover of labelled N in soil modifies the ratio of labelled to unlabelled available N and thereby affects the uptake of 15N by plants. The recovery of labelled N by maize was measured in a field experiment under three management systems, with one 15N‐labelled input in each: (1) conventional, with fertilizer side dressing, (2) low input, with vetch as a cover crop and fertilizer side dressing, and (3) organic, with vetch and composted manure. The NCSOIL model, which simulates C and N turnover in soil, was modified to include relevant processes related to the maize crop, and used to estimate the decomposition rate constant of vetch in the field by optimizing the simulated dynamics of labelled N uptake by maize against the measured results. A large input of C from mineralizable soil organic matter and root deposition was necessary to account for the recovery of fertilizer N by maize. Optimization of labelled N recovery in the low input system resulted in two optional rate constants for the decomposition of vetch: rapid decomposition (0.4 day−1) of a labile vetch pool (49% of total vetch N), or slow decomposition (0.008 day−1) of a single vetch pool. In the simulated organic system, where manure and vetch were incorporated at the same time, only a rapid decomposition of the labile component of vetch accounted well for the recovery of vetch N by maize. The prolonged recycling of N mineralized from the vetch, and its mixing with fertilizer side dressing in the low input system, reduced the recovery of vetch N even though it was mineralized rapidly. This demonstrates the difficulty in assessing the availability of N from organic materials.
Hydraulic and transport properties of the plant–soil system estimated by inverse modelling
Authors: Sonnleitner M. A. , Abbaspour K. C. , Schulin R. 
Published: March 2003

SummaryModelling soil water flow and solute transport under field conditions requires the knowledge of many parameters that are difficult to determine directly. Values determined on small isolated samples in the laboratory are often not representative of field situations. We investigated the applicability of inverse modelling to a soil–plant system in lysimeter experiments. We also tested whether parameters obtained from one experiment could be applied to another with the same soil. In a lysimeter planted with young trees, we first did a multistep drainage experiment and then a long‐term bromide tracer experiment with atmospheric boundary conditions at the soil surface. To estimate the unsaturated hydraulic properties, we linked the inverse program SUFI (Sequential Uncertainty FItting) to the flow and transport model HYDRUS5. A comparison of several scenarios showed that the resulting values of parameters depended strongly on the data used for calibration and the formulation of the objective function. The results suggested that inverse modelling could be used to identify important processes. Inversely obtained parameters gave better predictions for a second experiment when more variables were considered in the objective function and when the range of hydraulic conditions was wider. Furthermore, with retention curves directly fitted to measured water retention data we achieved acceptable results. Despite some limitations, the inverse approach was found to be a sound and useful procedure for estimating parameters of a complex system involving water uptake by roots, solute transport and unsaturated flow.
Population dynamics of the brown shrimp Crangon crangon L., in shallow areas of the German Wadden Sea
Authors: DEL NORTE‐CAMPOS A. G. C. , TEMMING A. 
Published: March 2003

AbstractSettlement, growth and mortality of the brown shrimp, Crangon Crangon L., were studied in the north Frisian Wadden Sea over a period of 19 months to fill existing gaps regarding the species' life cycle, and thereby to clarify points related to the fishery. Settlement of postlarval shrimp in the shallow areas occurred in three batches: in May; during summer; and an overwintering batch. Compared with an earlier model based on laboratory‐derived data, a new growth model based on field data predicts similar growth rates for the earlier phase of the shrimp life cycle, but higher rates for the later stages of the cohorts. Mean growth rate of the different cohorts over the size range sampled was 0.23 ± 0.08 mm day−1. Of the factors tested, only temperature significantly influenced growth rates. Preliminary estimates of instantaneous total mortality values for shrimp cohorts from these shallow areas ranged from 0.03 to 0.12 day−1. Salinity explained most of the variation in mortality rates, but this most likely indicates an indirect effect of depth on emigration. The cumulative effects of growth rates estimated from the new model and lower losses through predation could imply a higher contribution of winter eggs to the autumn fishery. This, however, needs further evaluation to properly quantify the trade‐offs between settlement and recruitment to the fishery, as well as the growth and mortality rates.
Status of the crucian carp, Carassius carassius (L.), in the UK
Authors: Wheeler A. 
Published: March 2003

SummaryThe crucian carp, Carassius carassius (L.), is a small fish of restricted distribution in the UK, which is probably only native to central and eastern England. The crucian carp is endemic to northern Europe. It has been widely confused with the introduced and congeneric goldfish, Carassius auratus (L.), and forms hybrids with that species and the introduced Cyprinus carpio L. The status of this fish has become confused with the presence of the congener and its hybrids, and it is now thought to be less frequent in occurrence than formerly.