Water and nitrate budgets in a rendzina cropped with oilseed rape receiving varying amounts of fertilizer

Pollution of the environment by nitrogen (N) has emerged as a serious concern in agriculture, especially in the case of crops such as oilseed rape. To assess the effect of N fertilization on N dynamics, the movements of water and nitrate were determined in a rendzina near Châlons-en-Champagne (eastern France) cropped with oilseed rape with three levels of fertilizer N and in a bare control. From in situ micrometeorological measurements, actual evapotranspiration rates were computed with an energy budget and used to calibrate an evapotranspiration model based on meteorological data and crop leaf area index. Water flow below 120 cm was then deduced from periodic measurements of soil moisture contents and precipitation, and the associated nitrate leaching fluxes were calculated from the NO₃ concentration measured at the same depth. Denitrification rates and ammonia volatilization were monitored in the field after fertilizer applications, and crop assimilation of nitrogen was determined frequently during the growth cycle. A nitrate budget gave an approximation of the in situ net mineralization fluxes. The water balance was influenced by the crop and its fertilization: the crop's canopy and roots enhanced the water loss by evapotranspiration and contributed to diminish the soil water storage, whereas drainage volumes were about the same for all cropped treatments, and significantly greater in the bare soil. The rainy winter was particularly favourable to leaching, and losses were much greater (+ 41%) under the over-fertilized crop than under the non-fertilized one, but remained less (– 42%) than those under the bare control soil. Bilans hydriques et azotés d'une culture de colza sur rendzine avec différentes doses d'engrais Les pollutions de l'environnement par l'azote sont devenues une préoccupation majeure en agriculture, particulièrement dans le cas des cultures comme le colza. Pour évaluer les effets de la fertilisation azotée sur la dynamique de l'azote, les transferts d'eau et de nitrate d'une rendzine ont été mesurés près de Châlons-en-Champagne (Est de la France) sur des parcelles expérimentales de colza avec trois niveaux de fertilisation azotée et sur une parcelle témoin en sol nu. A partir de mesures micrométéorologiques in situ, l'évapotranspiration réelle a été calculée par bilan énergétique de la surface du sol, et un modèle d'évapotranspiration ayant pour entrées des données météorologiques classiques et l'indice foliaire de la culture a été calibré. Le flux net d'eau sous 120 cm a été alors déduit de mesures périodiques de teneur en eau du sol et de précipitations, et les flux de nitrate associés ont été calculés à partir des concentration mesurées à la même profondeur. Les flux de dénitrification et la volatilisation d'ammoniac ont été mesurés au champ après les apports d'engrais; l'absorption d'azote par la culture a été déterminée fréquemment pendant le cycle de croissance. Enfin, un bilan azoté a donné l'ordre de grandeur de la minéralisation nette. Le bilan hydrique a été influencé par la culture et sa fertilisation: le couvert végétal et les racines ont accentué les pertes d'eau par évapotranspiration et par conséquent le stock d'eau, tandis que la lame d'eau drainée était à peu près la même pour tous les traitements cultivés, et significativement plus élevée pour le sol nu. L'hiver particulièrement pluvieux a été très favorable au lessivage, et les pertes ont été beaucoup plus fortes (+ 41%) sous la culture sur-fertilisée que sur la culture non-fertilisée, mais elles sont restées inférieures (– 42%) à celles sous sol nu. Nomenclature     

Comparing concurrent in situ and batch‐extracted trace element concentrations

Different procedures to investigate dissolved trace element concentration at the transition from unsaturated to saturated zone in soils were compared by concurrent sampling of soil solution and solid soil material in this zone. The in situ sampled soil solution from the percolated water was used to measure in situ concentrations, while solid soil material was used to measure concentrations at two liquid–solid ratios using batch experiments on 250 sample pairs. The liquid–solid ratios were 2 L kg^–1 and 5 L kg^–1. At 5 L kg^–1, the ionic strength was adjusted with Ca(NO₃)₂ to a sample‐specific value similar to in situ, while at 2 L kg^–1, the ionic strength was not adjusted. The extracted concentrations of most trace elements exhibited a statistically significant but weak correlation (p value < 0.01) to the corresponding in situ concentrations. In the liquid–solid ratio of 2 L kg^–1 extracts, Pb and Cr showed very poor comparability with the in situ equivalent. A likely cause was the enhanced dissolved‐organic‐C release in the extract due to the lower ionic strength compared to in situ conditions in combination with effects from drying and moistening soil samples. For the other elements, correlation increased in the order As < Cu, Zn, Sb, Mo, V < Cd, Ni, Co where adjustment of the ionic strength led to slightly better results. In addition to the element‐specific shortcomings, it appeared that low concentration levels of in situ concentrations were generally underestimated by batch extraction methods. The liquid–solid ratio of 2 L kg^–1 extracts could only be used as a method to predict exceedance of thresholds if a safety margin of approximately one order of magnitude higher than the thresholds was adopted. The ability of the batch‐extraction methods to estimate in situ concentrations was equally limited.     

Soil organic matter and nutrient pools under long‐term non‐burning management of sugar cane

We employed CP/MAS ¹³C NMR spectroscopy and classical humus fractionation to evaluate the behaviour of soil organic matter (SOM) resulting from long‐term sugar cane production when harvested without burning. Soil samples were collected at two depths (0–0.2 and 0.2–0.4 m) from a tropical Entisol cropped with sugar cane for 55 years at Campos dos Goytacazes (Brazil), either with or without burning crop residues when harvesting. Continuous incorporation of sugar cane residues increased carbon (C) content and promoted changes in SOM, including increases in humins, humic acids and aromatic C moieties. Sequential extraction methods showed enhanced amounts of available forms of nitrogen (N), sulphur (S) and phosphorus (P). Moreover, ³¹P NMR analysis revealed an increase in organic P as diester phosphates of plant origin in the humic acids fraction. The increased macronutrient bioavailability of labile forms of N, P and S could be partially related to the more hydrophobic nature of SOM observed in soil samples collected from areas that were not burnt. These results show that the long‐term non‐burning management of sugar cane harvest promotes the hydrophobic character of SOM and a more conservative and sustainable management of soil fertility. Matière organique du so let stockage de nutriments en manègement de longue durée et pas brûlé de la cane au sucre Résumé Le comportement de la matière organique du sol (MOS) a étéévalué sur une plantation de canne à sucre de longue durée, sans brûlis, par spectroscopie CP/MAS ¹³C NMR et la méthode classique de fractionnement et caractérisation de l’humus. Des échantillons de sol ont été prélevés dans une plantation de canne à sucre en culture continue depuis 55 ans, installée à Campos dos Goytacazes (Brésil) sur un entisol tropical. L’échantillonnage a été réaliséà 0–0.2 m et 0.2–0.4 m de profondeur sur des parcelles sous différents modes de mise en culture: parcelles comportant des récoltes précédées de brûlis des résidus et d’autres sans brûlis. L’incorporation continue des résidus de canne à sucre a provoqué l’augmentation du carbone (C) et des variations de la matière organique du sol (MOS), avec notamment l’augmentation des teneurs en humines, acides humiques et carbone aromatique. Les méthodes d’extraction séquentielle ont permis de détecter l’augmentation des quantités d’azote (N), de soufre (S) et de phosphore (P) disponibles. En outre, l’analyse RMN ³¹P effectuée sur les fractions d’acides humiques a révélé une augmentation des quantités de phosphore organique sous forme de diester de phosphates d’origine végétale. L’augmentation de la biodisponibilité de macronutriments (formes labiles de N, P et S) pourrait partiellement être attribuée au caractère hydrophobe de la matière organique plus expressif sur les échantillons de sol prélevés dans les parcelles sans brûlis. Ces résultats montrent que la pratique de non‐brûlis des résidus, à long terme, dans les plantations de canne à sucre, favorise le caractère hydrophobe de la matière organique du sol provoquant une gestion plus conservatrice et durable de la fertilité des sols.     

Measuring bioavailable trace metals by diffusive gradients in thin films (DGT): soil moisture effects on its performance in soils

Conventional methods of measuring labile chemical species of trace metals in soil solutions, such as chemical competition following centrifuging, are inadequate if the speciation changes during sampling and extraction. A new technique, diffusive gradients in thin films (DGT), measures labile species of trace metals in natural waters and sediments in situ. A well-defined diffusive gel layer distinguishes it from other resin-based techniques. It perturbs the soil in a controlled way by introducing an in situ local sink for metal ions. Resulting fluxes to the device are quantitatively measured, allowing assessment of re-supply kinetics and in some cases measurement of in situ soil solution concentrations. We used DGT to measure fluxes of Cd, Co, Cu, Ni, Pb and Zn in a sludge-treated soil at various moisture contents (27–106%). Replicate measurements showed that the precision of DGT-measured fluxes was within 10%. For moisture contents exceeding the field capacity (42%), the DGT response reflected soil water concentrations. At smaller moisture contents, changes related to tortuosity and dilution were reflected in the measurements. This technique has the potential for in situ measurements in the field where it should provide quantitative flux data on individual soils and provide a good surrogate for bioavailable metal.     

Amelioration of calcareous saline sodic soils through phytoremediation and chemical strategies

Abstract. The worldwide occurrence of saline sodic and sodic soils on more than half a billion hectares warrants attention for their efficient, inexpensive and environmentally acceptable management. These soils can be ameliorated by providing a source of calcium (Ca²⁺) to replace excess sodium (Na⁺) from the cation exchange sites. Although chemical amendments have long been used to ameliorate such soils, the chemical process has become costly during the last two decades in several developing countries. As a low‐cost and environmentally acceptable strategy, the cultivation of certain salt tolerant forage species on calcareous sodic and saline sodic soils, i.e. phytoremediation, has gained interest among scientists and farmers in recent years. In a field study conducted at three calcareous saline sodic sites (pH_s=8.1–8.8, EC_e=7.8–12.5 dS m^–1, SAR=30.6–76.1) in the Indus Plains of Pakistan, we compared chemical and phytoremediation methods. There were four treatments; two involved plants: Kallar grass (Leptochloa fusca (L.) Kunth), and sesbania (Sesbania bispinosa (Jacq.) W. Wight). The other two treatments were uncropped: soil application of gypsum and an untreated control. All treatments were irrigated with canal water (EC=0.22–0.28 dS m^–1). The plant species were grown for one season (5–6 months). Sesbania produced more forage yield (34 t ha^–1) than Kallar grass (23 t ha^–1). Phytoremediation and chemical treatments resulted in similar decreases in soil salinity and sodicity, indicating that phytoremediation may replace or supplement the more costly chemical approach. The soil amelioration potential of sesbania was similar to that of the Kallar grass, which suggests that moderately saline sodic calcareous soils can be improved by growing a forage legume with market value.     

Partitioning of metals (Cd, Co, Cu, Ni, Pb, Zn) in soils: concepts, methodologies, prediction and applications – a review

Prediction of the fate of metals in soil requires knowledge of their solid–liquid partitioning. This paper reviews analytical methods and models for measuring or predicting the solid–liquid partitioning of metals in aerobic soils, and collates experimental data. The partitioning is often expressed with an empirical distribution coefficient or K_d, which gives the ratio of the concentration in the solid phase to that in the solution phase. The K_d value of a metal reflects the net effect of various reactions in the solid and liquid phases and varies by orders of magnitude among soils. The K_d value can be derived from the solid–liquid distribution of added metal or that of the soil‐borne metal. Only part of the solid‐phase metal is rapidly exchangeable with the solution phase. Various methods have been developed to quantify this ‘labile’ phase, and K_d values based on this phase often correlate better with soil properties than K_d values based on total concentration, and are more appropriate to express metal ion buffering in solute transport models. The in situ soil solution is the preferred solution phase for K_d determinations. Alternatively, water or dilute‐salt extracts can be used, but these may underestimate in situ concentrations of dissolved metals because of dilution of metal‐complexing ligands such as dissolved organic matter. Multi‐surface models and empirical models have been proposed to predict metal partitioning from soil properties. Though soil pH is the most important soil property determining the retention of the free metal ion, K_d values based on total dissolved metal in solution may show little pH dependence for metal ions that have strong affinity for dissolved organic matter. The K_d coefficient is used as an equilibrium constant in risk assessment models. However, slow dissociation of metal complexes in solution and slow exchange of metals between labile and non‐labile pools in the solid phase may invalidate this equilibrium assumption.     

Aggregate stability of a crusted soil: differences between crust and sub‐crust material,and consequences for interrill erodibility assessment. An example from the Loess Plateau of China

Soil interrill erodibility is a key component of soil erosion models. However, when using aggregate stability to assess soil erodibility, samples are usually collected from the plough layer, while soil erosion occurs at the soil surface. Hence, the potential changes in erodibility caused by crusting are ignored. Moreover, soil interrill erodibility is difficult to predict accurately. This lack of predictability means that current erosion models use a constant erodibility value for a given soil, and thus do not consider potential heterogeneity of erodibility. This study was conducted to (i) assess the heterogeneity of aggregate stability for a crusted soil and (ii) relate this heterogeneity to the aggregate stability of the underlying material (sub‐crust) and to standard soil properties. A field study was conducted in a small area of the Loess Plateau in China in which the crust and the sub‐crust soils were sampled. Standard soil properties (organic matter content, sand content, silt content, clay content, cation exchange capacity (CEC), pH in water, and water content at the time of sampling) were measured as potential explanatory factors of aggregate stability. The results showed a large heterogeneity in aggregate stability among the sites, even though the sites had the same soil type. The mean weight diameter (MWD) of the crust varied between 0.33 and 2.04 mm while the MWD of the sub‐crust varied between 0.23 and 1.42 mm. Soil texture and pH were uniform among the sampling sites, whereas water content, organic matter content and CEC varied more. Even though some correlations existed (for example r = 0.57 between MWD for the slow wetting test and organic matter content), none of the standard soil properties was able to predict aggregate stability accurately. The aggregate stability of the crust was significantly greater than that of the sub‐crust. The large differences in aggregate stability imply large differences in soil interrill erodibility. Because a single soil type was investigated, this finding proves that erodibility can vary greatly in space even for a given soil type. Soil interrill erodibility should be estimated from the exact material exposed to erosive forces, the soil surface material. Using the sub‐crust would have led to greatly over‐estimated erodibility and thus to a marked bias in erosion model predictions. Résumé La stabilité structurale d'un sol encroûté : différences entre la croûte et le matériau sous‐jacent, et conséquences pour l'estimation de l'érodabilité inter‐rigole. Un exemple dans le Plateau de Loess (Chine) L'érodabilité inter‐rigole est un paramètre clef des modèles d'érosion du sol. Cependant, lorsque des tests de stabilité structurale sont utilisés pour évaluer l'érodabilité, les mesures sont habituellement réalisées sur des échantillons prélevés dans l'horizon labouré alors que l'érosion a lieu à la surface du sol. Ainsi, les changements potentiels d'érodabilité causés par la formation de croûte sont ignorés. De plus, l'érodabilité inter‐rigole reste encore difficile à prédire avec précision. Ces difficultés conduisent les modèles d'érosion à utiliser une érodabilité constante pour un type de sol donné, et donc à ne pas considérer l'hétérogénéité potentielle de l'érodabilité. Cette étude a été conduite pour (i) évaluer l'hétérogénéité de la stabilité structurale pour un sol encroûté et (ii) relier cette hétérogénéité à la stabilité structurale du matériau sous‐jacent (sous‐croûte) et aux propriétés standards du sol. Une étude de terrain a été réalisée sur un secteur de surface limitée du Plateau de L?ss (Chine). Des échantillons provenant de la croûte et de la sous‐croûte ont été collectés. Les propriétés standards (teneur en carbone organique, teneurs en sable, limon et argile, CEC, pH, et teneur en eau au prélèvement), ont été mesurées en tant que facteurs explicatifs potentiels de la stabilité structurale. Les résultats ont montré une grande hétérogénéité de la stabilité structurale entre les différents sites alors que ces derniers présentaient le même type de sol. Le MWD de la croûte variait entre 0.33 et 2.04 mm tandis que le MWD de la sous‐croûte variait entre 0.23 et 1.42 mm. La texture du sol et le pH étaient très homogènes entre les sites étudiés, tandis que la teneur en eau, la teneur en matière organique et la CEC variaient plus fortement. Bien que certaines corrélations aient été identifiées (par exemple r = 0.57 entre le MWD du test à l'humectation lente et la teneur en carbone organique), aucune de ces propriétés n'a permis de prédire précisément la stabilité structurale. La stabilité structurale de la croûte était significativement supérieure à celle de la sous‐croûte. Les grandes différences de stabilité structurale mesurées impliquent des érodabilités très contrastées. Comme un seul type de sol a été étudié, ce résultat prouve que l'érodabilité peut être très variable spatialement pour un type de sol donné. L'érodabilité inter‐rigole du sol devrait être mesurée sur le matériau exact qui subit l'érosion, c'est‐à‐dire le matériau de surface. L'utilisation du matériau sous‐jacent aurait engendré une forte surestimation de l'érodabilité et donc un biais important dans les prédictions d'un modèle d'érosion.     

Evaluating soil salinity status from bulk electrical conductivity and permittivity

In the range of volumetric water content, θ, from about 0.12 cm³ cm^–3 to saturation the relation between bulk electrical conductivity, C_b, and bulk electrical permittivity, ε, of mineral soils was observed to be linear. The partial derivative ?C_b/?ε appeared independent of the moisture content and directly proportional to soil salinity. We found that the variable X_s = ?C_b/?ε determined from in situ measurements of C_b(θ > 0.2) and ε(θ > 0.2) can be considered as an index of soil salinity, and we call it the ‘salinity index’. Knowing the index and sand content for a given soil we could calculate the electrical conductivity of the soil water, C_w, which is a widely accepted measure of soil salinity. The two variables from which the salinity index can be calculated, i.e. C_b and ε, can be read simultaneously from the same sensor by time-domain reflectometry. Quantities and symbols a constant /dS m^–1 b constant c constant /dS m^–1 C _b electrical conductivity of bulk soil /dS m^–1 C _b′ constant equal to 0.08 dS m^–1 C _s electrical conductivity of a solution used to moisten soil samples /dS m^–1 C _w electrical conductivity of soil water defined as the soil salinity /dS m^–1 C _wref reference salinity (that truly existing) resulting from the procedure of moistening samples, expressed as C_s + C_r/dS m^–1 C _r baseline value of C_s due to residual soluble salts present in the soil /dS m^–1 d constant D dry soil bulk density /g cm^–3 l slope r ratio S sand content /% by weight t time /s X _s salinity index /dS m^–1 X _si initial salinity index when distilled water is used to moisten soil samples /dS m^–1 Y a moisture-independent salinity-dependent variable /dS m^–1 z coordinate along direction of flow of the soil solution ε′ constant equal to 6.2 ε relative bulk electrical permittivity (dielectric constant) of the soil θ volumetric water content determined thermogravimetrically using oven-drying /cm³ cm^–3     

Selection and characterization of wheat genotypes for saline soils prone to water‐logging

Wheat (Tritcum aestivum L.) genotypes were screened and characterized for performance under salt stress and/or water‐logging. In a solution‐culture study, ten wheat genotypes were tested under control, 200 mM–NaCl salt stress and 4‐week water‐logging (nonaerated solution stagnated with 0.1% agar), alone or in combination. Shoot and root growth of the wheat genotypes was reduced by salinity and salinity × water‐logging, which was associated with increased leaf Na⁺ and Cl^– concentrations as well as decreased leaf K⁺ concentration and K⁺ : Na⁺ ratio. The genotypes differed significantly for their growth and leaf ionic composition. The genotypes Aqaab and MH‐97 were selected as salinity×water‐logging‐resistant and sensitive wheat genotypes, respectively, on the basis of their shoot fresh weights in the salinity × water‐logging treatment relative to control. In a soil experiment, the effect of water‐logging was tested for these two genotypes under nonsaline (EC = 2.6 dS m^–1) and saline (EC = 15 dS m^–1) soil conditions. The water‐logging was imposed for a period of 21 d at various growth stages, i.e., tillering, stem elongation, booting, and grain filling alone or in combinations. The maximum reduction in grain yield was observed after water‐logging at stem‐elongation + grain‐filling stages followed by water‐logging at grain‐filling stage, booting stage, and stem‐elongation stage, respectively. Salinity intensified the effect of water‐logging at all the growth stages. It is concluded that the existing genetic variation in wheat for salinity × water‐logging resistance can be successfully explored using relative shoot fresh weight as a selection criterion in nonaerated 0.1% agar–containing nutrient solution and that irrigation in the field should be scheduled to avoid temporary water‐logging at the sensitive stages of wheat growth.     

Methodologically controlled variations in laboratory and field pH measurements in waterlogged soils

We have tested the reliability and consistency of conventional pH measurements made on water‐soil mixtures with respect to sieving, drying, ratio of water to soil, and time of shaking prior to measurement. The focus is on a waterlogged soil where the preservation potential of archaeological artefacts is critical. But the study includes agricultural and forest soils for comparison. At a waterlogged site, laboratory results were compared with three different field methods: calomel pH probes inserted in the soil from pits, pH measurements of soil solution extracted from the soil, and pH profiles using a solid‐state pH electrode pushed into the soil from the surface. Comparisons between in situ and laboratory methods revealed differences of more than 1 pH unit. The content of dissolved ions in soil solution and field observations of O₂ and CO₂ concentrations were used in the speciation model PHREEQE in order to predict gas exchange processes. Changes in pH in soil solution following equilibrium in the laboratory could be explained mainly by CO₂ degassing. Only soil pH measured in situ using either calomel or solid‐state probes inserted directly into the soil was not affected by gas exchange processes. Variations on the order of 0.2–0.5 pH unit in different laboratory methods could not be explained by degassing and seem to be soil‐type specific and strongly influenced by drying and shaking. Further attention should be given to standardization of pH measurements, particularly before pH measurements from different soil types are compared.     

Washing procedure for mixed‐bed ion exchange resin decontamination for in situ nutrient adsorption

Abstract

Mixed‐bed cation + anion exchange resin bags are frequently used to assess in situ nutrient availability in forest soils, and have demonstrated their utility for comparing the impacts of different disturbances associated with treatments. They are generally installed in organic or mineral soil horizons for a certain time period, then recovered and extracted, to inform about nutrient availability during that period. For the method to be effective, the ion exchange sites of resins must be clear from any contaminants prior to installation in the soil. A washing procedure to be conducted before in situ burial of mixed‐bed resins was developed and is described. The IONAC NM‐60 H⁺/OH^‐ resins are consecutively washed with 2 N NaCl, deionized water, and 0.1 N NaOH. Finally, resins are rinsed with deionized water and stored moist and cold until bag preparation and burial in the soil.     

Reclamation of saline calcareous soils using vegetative bioremediation as a potential approach

Vegetative bioremediation of saline calcareous soil (EC_1:1 11.01 dS m^?1) was practised through growing fodder beet (Beta Beta vulgaris var. magnum) and millet (Panicum spp.) in soil columns. Beet was grown at a planting density of 4427 plants m^?2, whereas millet was grown at two planting densities: 5202 (M1) and 8928 (M2) plants m^?2. Some plants were irrigated with 233 μ S cm^?1 water throughout the experiment (70 days), while for others non-saline water was replaced with saline water (2.52 dS m^?1) at the middle of the experiment. The control was leaching of uncropped soil. Beet had higher ash content and efficiently extracted higher amount of salts (particularly Na and Cl) along with their aboveground biomass than millet under the two irrigation regimes. Millet grown at high planting density had higher ash content and extracted higher amount of salts (particularly Cl) than those at low planting density. Bioremediation, particularly in the case of millet (M1), considerably enhanced soil hydraulic conductivity as compared with leaching treatment; thus, facilitating the removal of some soluble salts beyond the root zone. Accordingly, soil electrical conductivity was considerably decreased by 54–69% compared with the untreated soil. It is concluded that mainly fodder beet is a potential candidate for efficient bioremediation of saline calcareous soils.

     

Sodium removal from a calcareous saline–sodic soil through leaching and plant uptake during phytoremediation

Saline–sodic and sodic soils are characterized by the occurrence of sodium (Na⁺) to levels that can adversely affect several soil properties and growth of most crops. As a potential substitute of cost‐intensive chemical amelioration, phytoremediation of such soils has emerged as an efficient and low‐cost strategy. This plant‐assisted amelioration involves cultivation of certain plant species that can withstand ambient soil salinity and sodicity levels. It relies on enhanced dissolution of native calcite within the root zone to provide adequate Ca²⁺ for the Na⁺ Ca²⁺ exchange at the cation exchange sites. There is a lack of information for the Na⁺ balance in terms of removal from saline–sodic soils through plant uptake and leaching during the phytoremediation process. We carried out a lysimeter experiment on a calcareous saline–sodic soil [pH of saturated soil paste (pH_s) = 7.2, electrical conductivity of the saturated paste extract (EC_e) = 4.9 dS m⁻¹, sodium adsorption ratio (SAR) = 15.9, CaCO₃ = 50 g kg⁻¹]. There were three treatments: (1) control (without application of a chemical amendment or crop cultivation), (2) soil application of gypsum according to the gypsum requirement of the soil and (3) planting of alfalfa (Medicago sativa L.) as a phytoremediation crop. The efficiency of treatments for soluble salt and Na⁺ removal from the soil was in the order: gypsum ≈ alfalfa > control. In the phytoremediation treatment, the amount of Na⁺ removed from the soil through leaching was found to be the principal cause of reduction in salinity and sodicity. Copyright © 2003 John Wiley & Sons, Ltd.     

Similarities in chemical composition of soil organic matter across a millennia-old paddy soil chronosequence as revealed by advanced solid-state NMR spectroscopy

This study examined the chemical composition of soil organic matter (SOM) along a 2,000-year paddy soil chronosequence in eastern China by use of advanced solid-state nuclear magnetic resonance (NMR) spectroscopy as well as Fourier transform infrared spectroscopy (FTIR), aiming to identify changes in the chemical composition of SOM over a millennium timescale. The results showed that soil organic carbon concentration in the surface soil reached a steady state after 100 years of rice (Oryza sativa L.)–wheat (Triticum sp.) cropping on coastal tidal flats. The ¹³C NMR spectra and fractions of structural groups or components of the whole SOM samples differed little along the chronosequence, suggesting a similar chemical composition in SOM samples regardless of the duration of rice cultivation. The FTIR spectral pattern and relative intensities of some resolved functional groups or components of whole SOM were also similar along the soil chronosequence. The similarities in chemical composition of SOM can be attributed to the rice–wheat cropping system, in which SOM has undergone ongoing turnover under periodical fresh plant material input and wet–dry cropping alternation, leading to a similar chemical composition of bulk SOM.     

Suitability of the ESS laboratory method to determine the equilibrium soil solution composition of agricultural soils,and suggestions for simplification of the experimental procedure

The proper selection of the background electrolyte is of special importance studying element availability and mobility in the laboratory. The determination of the background solution composition can be done with the equilibrium soil solution method ESS (Matschonat and Vogt, 1997). The ESS method is a procedure to find out a salt solution of major cations and anions that does not undergo changes in its composition when brought into contact with a specific soil sample. This composition is experimentally approximated in an iterative procedure until certain quality criteria are fulfilled. We tested if the ESS method, which was developed for forest soils, can successfully be applied also to agricultural soils. The solution composition was confirmed by an independent method. We used samples of a glasshouse and an arable loess soil. Because the ESS method is relatively time and work consuming, we tested modifications which should simplify the procedure: the use of dried and frozen samples instead of field fresh soil, an approximation according to the solution's electric conductivity only, and the modeling of cation exchange to omit iteration steps. The ESS method caused slight overestimation (10–25 %) in cation concentrations, but in general, these were well met. Individual anion concentrations, however, were not buffered in this soil and could not unequivocally be determined. We recommend to adjust the anion concentrations in the ESS procedure according to their proportions in an initial water extract. As ion concentrations are functions of the soil : solution ratio, any method based on addition of water to the soil, like the so‐called soil saturation extract (Germany: Bodensättigungsextrakt), runs a risk to seriously underestimate ion concentrations at field conditions. The ESS method may therefore be especially well suited for soils with a low water content. The use of frozen soil gave good results and the omission of iteration steps by cation exchange modeling was promising and will be explored with the aim to operationalize it in forthcoming work.     

Sustainable Management of Landfill Leachate by Irrigation

Leachate from domestic landfills is a significant environmentalhazard. In the urban environment, irrigation of recreational turf and parkland with nitrogen-rich landfill leachate providesboth low-cost treatment that minimises pollution of surroundingwaters and a valuable water resource. Of particular interest isthe capacity of the turf-soil system to ameliorate the ammonium-rich leachate. To address this issue, a two-year field trial was completed at the Newington Landfill irrigating with saline,ammonium-rich leachate. The field trial suggested that in situ bioremediation is sustainable provided that management strategies such as dilution of leachate to reduce solution electrical conductivity to 3.6 dS m^-1 are adopted. Furthermore, pollution due to leaching of nitrogen can be minimised by managing the soil to enhance in situ denitrification of applied nitrogen. The management regimes adopted during the Newington field trial enabled nitrogen application rates in excess of 1400 kg NH₄ ⁺ha^-1 yr^-1. However, the capacity of the system to ameliorate the leachate appears limited by soil salinity and sodicity rather than the control of nitrogen leaching by denitrification,suggesting that rates of up to 3500 kg NH₄ ⁺ha^-1 yr^-1 may be viable if the salinity hazard can be effectively managed.     

Polyethersulfone Membrane Filters for Sampling Soil Water from In Situ Soils and Intact Soil Columns for Phosphate Analysis

Abstract

Porous plates or cups are commonly used to collect soil solution samples in field studies or from intact soil columns. Some commonly used materials for porous plates may adsorb soil solution constituents such as phosphorus (P). An alternative to using a porous plate is to use a membrane filter with a known pore size and bubble point. The objective of this study was to evaluate the utility of polyethersulfone membranes (pore size 0.45 µm and bubble point >200 kPa) to extract soil solution from in situ soils and intact soil columns for phosphate analysis. In situ soil solution samplers were constructed from modified reusable polysulfone membrane filter holders equipped with polyethersulfone membranes (47 mm diameter). A ?10 kPa vacuum was maintained in the samplers, which enabled soil solution collection at soil water potentials of 0 to ?4 kPa in loamy sand, 0 to ?10 kPa in sandy loam, and 0 to ?12 kPa in sandy clay loam soils. In a laboratory study, soil solution samplers continued to hold a vacuum to ?77 kPa soil water potential. Soil solution samplers were further evaluated in a field study at 45‐, 90‐, and 135‐cm depths in two soils. Samplers operated with relatively few difficulties for the first 12 months of field evaluation. Membranes apparently dried during periods of low soil water potential but increases in soil moisture were sufficient to rewet the membrane. Sampler failures in the field increased during 13–18 months because aged vacuum tubing and root interferences with samplers at 45 cm. Improvements in sampler design may improve the durability for implementation in long‐term field experiments. Membrane filters worked near flawlessly to maintain unsaturated conditions in intact soil columns. The filter units facilitated easy collection of soil water from the intact soil columns without altering the chemical composition of the percolate.     

Effects of seasonal rainfall and water table movement on the soil solution composition of tropical peatland

ABSTRACT

Understanding the composition of the soil solution of tropical peatlands is important because it directly affects nutrient availability and environmental degradation. The objectives of this study were to investigate temporal fluctuations in the soil solution composition in tropical peatlands in West Kalimantan and Riau, Indonesia and identify the factors controlling these fluctuations. In each site, we established four study plots consisting of three plots under oil palm (Elaeis guineensis Jacq.) plantation and one plot under uncultivated land as the control. Triplicate soil solution samples were collected at 50 and 200 cm depths, fortnightly. During the drought, the pH at 50 cm was low (3.7–4.0), which was influenced by oxidation reactions such as organic acids and NO₃^? generations. The pH at a depth of 200 cm was high (5.9–6.8), due to reduction reactions such as denitrification. High cation concentrations at both depths would result from organic matter decomposition and the limited downward movement of water. Rewetting the West Kalimantan peatland caused a sharp decrease in pH and ionic concentrations at 50 and 200 cm depths, because of the transportation of ions from the upper acidified layer. However, the lower rainfall levels in Riau than West Kalimantan resulted in a gradual decrease in pH and Ca²⁺ concentration. The higher pH levels and ion concentrations in West Kalimantan than in Riau would be influenced by the enhanced microbial activity due to water supply from the risen water table in this site. This study showed that seasonal rainfall and water table movement were the main factors controlling the fluctuations in the chemical composition of soil solutions.     

Rainforest litter quality and chemical controls on leaf decomposition with near‐infrared spectrometry

Plant‐litter chemical quality is an important driver of many ecosystem processes, however, what actually constitutes high‐ or low‐quality litter (chemical potential for fast and slow decomposition, respectively) is often interpreted by the indices available. Here, near‐infrared spectroscopy (NIRS) was used to explore leaf‐litter chemical quality and the controls on decomposition in the tropical rainforest region of north Queensland Australia. Leaf‐litter samples from litterfall collections and litterbag studies were used. NIRS was used to calibrate the chemical compositions of the material (N, P, C, Mg, Ca, acid detergent fiber, acid detergent lignin, α‐cellulose, and total phenolics) from a smaller sample set covering the spectral range in the full set of samples. Calibrations were compared for both separate (local) and combined models, for litterbags, and litterfall. Coefficients of determination (r²) in the local models ranged from 0.88 (litterbag Mg) to 0.99 (litterfall N), with residual prediction deviation ratios > 3 for all constituents except Mg (≈ 2.5). Mass loss in the litterbags was strongly related to the NIR spectra, with model r²'s of 0.75 (in situ leaves) and 0.76 (common control leaf). In situ decomposability was determined from modeling the initial NIR spectra prior to decomposition with litterbag exponential‐decay rates (model r² of 0.81, n = 85 initial samples). A best subset model including litter‐quality, climate, and soil variables predicted decay better than the NIR decomposability model (r² = 0.87). For litter quality alone the NIR model predicted decay rate better than all of the best predictive litter–chemical quality indices. The decomposability model was used to predict in situ decomposability in the litterfall samples. The chemical variables explaining NIR decomposability for litterfall were initial P, C, and phenolics (linear model r² = 0.80, n = 2471). NIRS is a holistic technique that is just as, if not more accurate, than litter–chemical quality indices, when predicting decomposition and decomposability, shown here in a regional field study.