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Context. Soils irrigated with wastewater are generally phosphorus (P)-enriched. P losses from these soils may impair surface water quality. However, wastewater applications also alter soil pH and P availability. Aims. We investigated if amending soils with aluminium (Al), iron (Fe) or calcium (Ca) sorbents could decrease the potential for P losses despite altering soil pH and potentially increasing soil P availability. Methods. Seven soils (pH 5.3-6.9) were incubated with lime, gypsum, hydrotalcite, alum sulfate, ferric sulfate, and ferric chloride at rates of 0:1, 0.25:1, 0.5:1 and 1:1 molar ratios of Al/Fe to P, and 0:1, 0.5:1, 1:1 and 5:3 for Ca to P, respectively. After 21 days pH and water extractable P (WEP) were measured. Key results. In most cases the application of Al, Fe and Ca amendments decreased WEP in proportion to the rates applied. However, poor performance was noted when amendments were mismatched to soils altering their pH into the range where high soil P availability was expected. Of the amendments used, alum and iron sulfate were the most cost-efficient. However, even when optimised and applied to critical source areas the estimated cost-effectiveness of these amendments is still poor and may only be effective in the short term. Conclusions and implications. We therefore recommend that other strategies such as inversion tillage bringing low P topsoil to the surface (and decreasing the potential for P loss by surface runoff) together with changes in the farm system to extract more P from the topsoil are the only strategies that will decrease the potential for P loss cost-effectively and in the long-term. Keywords: aluminium, dairy, effluent, grassland, iron, management, mitigation, wastewater., Introduction Irrigation with phosphorus (P)-rich dairy factory wastewater can result in the enrichment of P in the topsoil (Degens et al. 200) ; Elliott et al. 200! ; Liu and [...]

Context. Success of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is dependent on a range of soil factors including pH and soil organic carbon (OC) content. Aims. This study identified the effect of soil properties and moisture content at the time of DMPP application on the efficiency of DMPP and soil mineral N concentrations. Methods. Soil was collected from paired paddocks with contrasting management, cropping or pasture across three sites. Soil samples were pre-incubated for 7 days with moist (-85 kPa) or air dried soil to simulate sowing into soil with moisture equivalents of post seasonal break or dry sowing. Urea ammonium nitrate (UAN) was applied with and without DMPP to all soils. Key results. DMPP inhibited nitrification in all soils, although decreased inhibitory effectiveness was observed in acidic soils compared to neutral soils. Inhibition efficacy on acidic soils was improved when DMPP was applied to dry rather than wet soils. Neutral soils did not observe the same soil moisture effect having similar inhibition efficiency of DMPP observed between dry and wet soil application. Nitrogen fertilisers applied to dry soils nitrified at a greater rate than when applied to wet soils. DMPP decreased the ammonia oxidising bacteria (AOB) population while the ammonia oxidising archaea (AOA) amoA gene copy numbers were unaffected. Conclusions. This study shows that the lower soil pH and high OC contents can reduce the efficacy of DMPP. Implications. When using DMPP in Australian broad acre agriculture, knowledge of soil properties including soil pH will determine if application of DMPP is suitable for use before or after a seasonal break rainfall event. Keywords: amoA, AOA, AOB, DMPP, mineralisation, nitrification inhibitor, priming effect, pre-incubation., Introduction The biological oxidation of ammonium (N[H.sub.4.sup.+]) is performed by ubiquitous soil microorganisms called nitrifiers. Aerobic, chemoautotrophic ammonia oxidising bacteria (AOB) and archaea (AOA) oxidise N[H.sub.4.sup.+] to the intermediate hydroxylamine [...]

The combination of high aluminium (Al) saturation and severe phosphorus (P) deficiency in subsurface soil in no-tillage (NT) systems is an obstacle hampering crop yields in Brazil. The introduction of NT without proper soil chemical correction affects crop yields in several parts of the country. The aim of this study was to evaluate the changes in soil chemical properties and response of crops to different application methods of lime and phosphate fertiliser in an Ultisol under NT. The field experiment consisted of combining surface and incorporated liming and P application (without P, surface P and P in the sowing line), plus a treatment with incorporated lime and P. The correction of soil acidity and availability of P at depth was effective with the incorporation of lime and phosphate fertiliser. Five months after lime incorporation, it was possible to increase soybean productivity by more than 40% (from 3.9 to 5.6 Mg [ha.sup.-1]). The surface application of P and limestone restricts the correction of soil fertility only in the uppermost soil layer evaluated (up to 5 cm). The relationship between soybean yield and soil chemical properties in different layers clearly demonstrates that neither the 0-10 cm soil layer nor the 0-20 cm soil layer is suitable for diagnosing soil fertility and the crop productive potential in NT system with chemical restrictions in subsurface. Further studies are need to establish critical levels of available P and Al saturation for subsurface soil layers in different soil types under no-tillage. Keywords: aluminum toxicity, crop productivity, fertilisation, lime application, phosphate chemistry, soil acidity, soybean, weathered soils., Introduction In Brazil, the cultivated area remained stable at 39 million ha between 1977 and 2001, jumping to 47 million ha in the 2004-2010 period and reached 61 million ha [...]

This study aimed to ascertain whether application of sheep urine led to the development of acidic subsurface layers of a pasture soil. Deionised water or simulated urine solution delivering urea-nitrogen (N) at 44.8 g [m.sup.-2] and potassium at 25 g [m.sup.-2] was applied to soil in either winter or spring. Treatments were applied to the soil surface within 10.3 cm internal diameter PVC tubes inserted 20 cm into the soil either under ryegrass or kept bare. Main sampling times corresponded to the completion of various soil N transformations as determined by periodic sampling. Main samplings involved the collection of above ground plant material and soil sampling in 2 cm depth increments in 0-10 cm and 5 cm intervals in 10-20 cm depths. Following treatment application, urea and ammonium-N moved to a depth no greater than 20 cm but the extent of movement was greater in winter than spring due to the influence of initial soil moisture. Following urea hydrolysis, soil pH increased in the 0-15 cm depth. Subsequent nitrification significantly acidified soil under pasture by 0.8-1.0 pFI units in the 2-8 and 2-6 cm depths in winter and spring respectively. This created a net acidic subsurface layer of 0.2-0.4 pH units compared with soil at the beginning of the experiment. Subsurface acidification was 0.5-0.7 pH units greater in bare soil compared with the presence of pasture. Transformations of N resulting from application of simulated urine solution formed acidic subsurface layers in the field regardless of the season of application. Additional keywords: acidification, acidity, nitrogen transformations, pastures, stratification, urine. Received 23 April 2020, accepted 8 July 2020, published online 6 August 2020, Introduction Soil acidification is one of the major factors limiting agricultural production in much of Australia (Helyar et ai 1990; Ridley et al. 1990) and internationally (von Uexkull and Mutert [...]

The objective of this laboratory incubation study was to assess the effectiveness and longevity of urease inhibitor N-(2-nitrophenyl) phosphoric triamide (2-NPT), along with the commonly used N-(n-butyl) thiophosphoric triamide (nBTPT), in reducing ammonia (N[H.sub.3]) emissions from cattle urine applied to pasture soils. It was hypothesised that 2-NPT would be effective as a longer-lasting inhibitor to reduce emissions after the deposition of urine during multiple grazing events. Two dairy-grazed pasture soils (Fluvisol, Rangitikei loamy sand (RLS) and Andosol, Egmont black loam (EBL)) with contrasting organic carbon levels and urease activity were used. The following treatments were applied to the soils at the start of the experiment: no inhibitor, nBTPT-low, 2-NPT-low, 2-NPT-medium and 2-NPT-high. Urine-N was applied to all the treatments at four stages: immediately before inhibitor application (Stage A), 29 days after inhibitor application (Stage B), 56 days after inhibitor application (Stage C) and 29 days and again 60 days after inhibitor application (Stage D); N[H.sub.3] emissions were measured up to Day 31 after each urine application. The low, medium and high application rates of inhibitors were determined based on achieving 0.025%, 0.050% and 0.075% of quantity of urine-N applied in Stage A respectively. For the no inhibitor treatment, the proportion of total applied N in urine that was emitted as N[H.sub.3] for the different stages ranged from 35.8% to 50.5% for RLS soil and from 14.2% to 26.7% for EBL soil. For Stage A, both inhibitors equally reduced N[H.sub.3] emissions from applied urine in both soils (23.7-27.3% for the RLS and 20.6-27.2% for the EBL). For Stage B, significant reductions (4.2-13.4%) in N[H.sub.3] emitted was observed only from RLS soil, with there being a significantly greater reduction from 2-NPT than from nBTPT, and 2-NPT continued to reduce N[H.sub.3] emissions at Stage C (5.6-7.4%). There was no reduction in emissions during Stage D by either of the inhibitors. The results of this study suggest that 2-NPT can extend the longevity of urease inhibition and reduce N[H.sub.3] emissions compared with the more commonly used inhibitor nBTPT in dairy-grazed pasture soils. Additional keywords: dairy soils, environmental degradation, nitrogen loss, nitrogen use efficiency, soil pH, urea hydrolysis. Received 11 November 2018, accepted 31 May 2019, published online 23 July 2019, Introduction The intensification and expansion of dairy farming in New Zealand (NZ) over the past three decades has resulted in a significant rise in the amount of cattle urine being [...]

The genus Drosera (sundews) is represented in British Columbia (BC), Canada, by Drosera rotundifolia (L.), Drosera anglica (Huds.), and their hybrid Drosera x obovata (Mert. & W.D.J. Koch). All three can be found in Sphagnum bogs of central BC, including those within the Aleza Lake Research Forest (ALRF) located 60 km east of Prince George. Vegetation patterns in bogs are known to be correlated with light, water, and nutrient gradients, and despite information being available on the influence of light and water on Drosera occurrence, little information is known about the role of nutrients. Here, we focused on a bog containing all three Drosera species, to determine whether nutrient levels are related to the abundance of the widespread species, D. rotundifolia. Univariate regression tree analysis between soil water chemistry and D. rotundifolia numbers indicates that D. rotundifolia is a calcifuge, preferring moderately acidic soil pH (>5.5) and relatively low calcium levels ( Key words: Drosera rotundifolia, Drosera anglica, calcium, Sphagnum peatlands, carnivorous plants. Le genre Drosera (<>) est represente en Colombie-Britannique (CB), au Canada, par Drosera rotundifolia (L.), Drosera anglica (Huds.) et leur hybride Drosera x obovata (Mert. & W.D.J. Koch). Tous trois peuvent se trouver dans les tourbieres du centre de la CB, incluant les tourbieres de la foret d'enseignement et de recherche d'Aleza Lake situee a 60 km a l'est de Prince George. Les patrons de vegetation des tourbieres sont connus pour etre correles avec les gradients de lumiere, d'eau et de nutriments, et malgre le fait que l'information sur l'influence de la lumiere et de l'eau sur la presence de Drosera soit disponible, le role des nutriments est peu connu. Les auteurs se concentrent ici sur une tourbiere comportant les trois especes de Drosera afin de determiner si les niveaux de nutriments sont relies a l'abondance de l'espece repandue D. rotundifolia. L'analyse d'un arbre de regression multivariable entre la chimie de l'eau du sol et le nombre d'individus indique que D. rotundifolia est un calcifuge, preferant les sols a pH moderement acides (5,5) et a niveaux de calcium relativement faibles ( Mots-cles: Drosera rotundifolia, Drosera anglica, calcium, tourbieres, plantes carnivores., Introduction Members of the sundew genus Drosera represent a number of scientifically important species. Widely known for their carnivorous habit, sundews are key models for ecological processes such as plant [...]

The distribution of tropical forest biomass across the landscape is poorly understood, particularly in increasingly common secondary tropical forests. We studied the landscape-scale distribution of edaphic properties, plant community characteristics, and aboveground biomass (AGB) in secondary tropical dry forests in northwest Costa Rica. We used structural equation modeling to examine conceptual models of relationships among these factors, with data from 84 0.1 ha plots. Stand age and soils explained 33%-60% of the variation in community-weighted mean values of foliar traits including specific leaf area, foliar nitrogen, phosphorus, and δ[sup.13]C. Aboveground biomass ranged from 1.7 to 409 Mg x [ha.sup.-1] among plots between 5 and >100 years old. Stand age alone explained 46% of the variation in AGB among plots, while a model including age, soil pH, traits, and forest type explained 58%. Stand age was the most important variable explaining the distribution of AGB and community characteristics in secondary forests. We speculate that plot size, landscape heterogeneity, disturbance history, and stand dynamics contribute to the unexplained variation in AGB across the landscape. Key words: aboveground biomass, succession, plant functional traits, structural equation modeling, tropical dry forest, secondary forest. La repartition de la biomasse de la foret tropicale dans le paysage est mal connue, particulierement dans les forets tropicales secondaires de plus en plus courantes. Nous avons etudie la repartition a l'echelle du paysage des proprietes edaphiques, des caracteristiques des communautes vegetales et de la biomasse aerienne (BA) dans les forets tropicales secondaires seches du nord-ouest du Costa Rica. Nous avons utilise la modelisation par equation structurelle pour examiner des modeles conceptuels des relations entre ces facteurs avec des donnees provenant de 84 placettes de 0,1 ha. L'age du peuplement et les sols expliquaient 33%-60% de la variation de la valeur moyenne des traits foliaires ponderee par les communautes incluant la surface foliaire specifique, la teneur en azote et en phosphore des feuilles et δ[sup.13]C. La BA variait de 1,7 a 409 Mg x [ha.sup.-1] parmi les placettes ou l'age du peuplement se situait entre 5 et >100 ans. L'age du peuplement seul expliquait 46% de la variation de la BA dans les placettes, tandis qu'un modele qui incluait l'age, les caracteristiques et le pH du sol ainsi que le type forestier expliquait 58%. L'age du peuplement etait la plus importante variable pour expliquer la repartition de la BA et les caracteristiques des communautes dans les forets secondaires. Nous croyons que la dimension de la placette, rheterogeneite du paysage, les perturbations passees et la dynamique du peuplement contribuent a la partie inexpliquee de la variation de la BA dans le paysage. [Traduit par la Redaction] Mots-cles: biomasse aerienne, succession, traits fonctionnels des plantes, modelisation par equation structurelle, foret tropicale seche, foret secondaire., Introduction Tropical forests store more carbon than boreal or temperate forests and are central to our understanding of both the global carbon cycle and the climate system (Bonan 2008). Despite [...]

: Atmospheric pollution levels in China are increasing quickly. Experience from other polluted regions shows that tree growth could be affected, but long-term effects of N deposition and soil acidification on Chinese forests remain mostly unknown. Soil acidification and N deposition were simulated for Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations managed for three consecutive 20-year rotations in southeastern China. A factorial experiment combined four rain pH levels (2.5, 4.0, 5.6, and 7.0), four N deposition rates (1, 7.5, 15, and 30 kg N * [ha.sup.-1] * [year.sup.-1]), and two site qualities (poor and rich). Results indicate that atmospheric pollution effects are not immediate, but after one to two rotations, soil acidification effects could reduce ecosystem C pools significantly (-25% and -11% in poor and rich sites, respectively). N deposition rates above 15 kg N * [ha.sup.-1] * [year.sup.-1] could offset some of the negative effects of soil acidification and lead to more ecosystem C (19 and 28 Mg C * [ha.sup.-1] more in poor and rich sites, respectively, than in low N deposition). However, at high N deposition rates (> 15 kg N * [ha.sup.-1] * [year.sup.-1]), N leaching losses could greatly increase, reaching 75 kg N * [ha.sup.-1] * [year.sup.-1]. Moderate N deposition could increase tree biomass production and soil organic mass, resulting in increased ecosystem C, but these gains could be associated with important N leaching. Atmospheric pollution could also result in the long term in nutrient imbalances and additional ecological issues (i.e., biodiversity loss, eutrophication, etc.) not studied here. Resume: Les niveaux de pollution atmospherique augmentent rapidement en Chine. L'experience d'autres regions aux prises avec la pollution montre que la croissance des arbres pourrait etre ralentie mais les effets a long terme des depots azotes (N) et de l'acidification des sols dans les forets chinoises sont pratiquement inconnus. L'acidification du sol et les depots de N ont ete simules dans des plantations de sapin de Chine (Cunninghamia lanceolata (Lamb.) Hook.) amenagees pendant trois rotations consecutives d'une duree de 20 ans dans le sudest de la Chine. Une experience factorielle a combine quatre niveaux de pluie acide (pH 2,5, 4,0, 5,6 et 7,0), quatre taux de deposition de N (1, 7,5, 15 et 30 kg N * [ha.sup.-1] * [year.sup.-1]) et deux qualites de station (pauvre et riche). Les resultats montrent que les effets de la pollution atmospherique ne sont pas imme-diats, mais qu'apres une a deux rotations, les effets de l'acidification du sol pouvaient reduire de facon significative les reserves de carbone (C) de l'ecosysteme (-25 et -11 % respectivement dans les stations pauvres et riches). Les taux de deposition de N plus eleves que 15 kg N * [ha.sup.-1] * [year.sup.-1] pouvaient attenuer certains des effets negatifs de l'acidification du sol et ont mene a plus de C de l'ecosysteme (19 et 28 Mg C * [ha.sup.-1] de plus respectivement dans les stations pauvres et riches qu'a-vec un faible taux de deposition de N). Cependant, les pertes de N par lessivage pouvaient augmenter de facon importante, jusqu'a 75 kg N * [ha.sup.-1] * [an.sup.-1], lorsque le taux de deposition de N etait eleve (> 15 kg N * [ha.sup.-1] * [year.sup.-1]). Un taux de deposition de N modere pouvait augmenter la production de biomasse des arbres et la masse de sol organique, ce qui a entraine une augmentation du C de l'ecosysteme, mais ces gains pouvaient etre associes a un lessivage important de N. La pollution atmosphe-rique pourrait aussi entrainer des desequilibres nutritifs a long terme et d'autres problemes d'ordre ecologique (c.-a-d. perte de biodiversite, eutrophisation, etc.) qui n'ont pas ete etudies ici. [Traduit par la Redaction], Introduction Concern about the possible effects of acid rain in China emerged in the late 1970s (Fan and Wang 2000), with the first reports appearing in the international literature in [...]

Ontario's hardwood forests are currently subjected to high levels of air pollution, but critical levels at which point adverse effects may occur are poorly known. In this study, we sampled 35 hardwood plots dominated by sugar maple (Acer saccharum Marsh.) located along a contrasting climate, soil acidity, and air pollution gradient in southern Ontario to explore relationships between these potential ecosystem stressors and ecosystem responses. Foliar sulfur (S) and nitrogen (N) contents were positively correlated with modeled deposition, and foliose lichen species richness was negatively correlated with modeled air pollution levels (S deposition, N deposition, and atmospheric ozone AOT40), whereas foliar calcium, magnesium, and manganese contents were correlated with A-horizon soil acidity. Forest floor S and N contents and C/N ratios were related to soil pH, with high S and N contents and low C/N ratios occurring on the more acidic soil in the northern part of the region, which receives the lowest modeled loadings of S and N deposition and experience colder and wetter climate. Forest health as determined by canopy condition was not related to indices of air pollution, climate, or soil acidity, and no relationship was found among air pollution, soil acidity, and ground vegetation species richness or diversity. Resume: Les forets feuillues ontariennes sont actuellement exposes a des niveaux eleves de pollution de l'air mais les niveaux critiques susceptibles d'avoir des effets nefastes sont mal connus. Dans cette etude, nous avons echantillonnes 35 parcelles feuillues dominees par l'erable a sucre (Acer saccharum Marsh.), etablies dans le sud de l'Ontario de telle sorte que les conditions climatiques, l'acidite du sol et la pollution de l'air variaient graduellement, pour etudier les relations entre ces stress potentiels et les reactions de l'ecosysteme. La teneur en azote (N) et soufre (S) des feuilles etait positivement correelee avec les depots modelises et la richesse en especes de lichens foliaces etait negativement correlee avec les niveaux modelises de pollution de l'air (depots de S et N, ozone AOT40), tandis que la teneur en calcium, magnesium et manganese des feuilles etait correlee avec l'acidite du sol dans l'horizon A. Dans la couverturemorte, S, N et le rapport C/N etaient relies au pH du sol; la teneur en S et N etait elevee et le rapport C/N etait faible sur les sols plus acides dans la partie nord de la region qui recevait les plus faibles quantites modelisees de depots de S et N et ou le climat etait plus froid et plus humide. Sur la base de l'etat du couvert, l'etat de sante de la foret n'etait pas relie aux indices de pollution de l'air, ni au climat, ni a la diversite du sol et aucune relation n'a ete observee entre la pollution de l'air, l'acidite du sol et ou la richesse en especes de la vegetation au sol. [Traduit par la Redaction], Introduction Chronic exposure to ground-level ozone, acid deposition, and deposition of nitrogen (N) compounds exert multiple stresses on forested communities. Because of concerns over the impacts of air pollutants on [...]

Although chlorites are an important source of Mg and micronutrients in soils, little is known about their weathering behavior in acidic environments. The effect of organic (acetic, oxalic, citric) and inorganic (hydrochloric, nitric, sulfuric) acids on the dissolution of ripidolite was studied at 25[degrees]C over an acid concentration range of 0.03 to 10 mM. The increasing ripidolite dissolution with increasing acid concentration can be described by the same empirical equation for all six acids used in this study. Because proton and ligand promoted dissolution mechanisms are additive, the influence of ligands can be calculated by subtracting the influence of protons from the total dissolution of ripidolite. We assume that the influence of [Cl.sup.-] in HCl systems can be neglected. Greater dissolution of ripidolite in the presence of the other acids at the same pH is attributed to the accompanying anion. At pH 3.5 and an anion concentration of [10.sup.-3.5] mol [L.sup.-1], the relative effectiveness of the acids used in this experiment in promoting dissolution was nitric (enhancement factor: 0.97) [congruent to] hydrochloric (1.00) [congruent to] acetic (1.01) < sulfuric (1.19) < citric (2.70) < oxalic acid (3.27). The dissolution of ripidolite was nonstoichiometric with a preferential release of Si relative to Al, Fe, and, in some cases, Mg at low proton and ligand concentrations for all six acids. At higher acid concentrations the dissolution becomes almost stoichiometric in the presence of inorganic acids, whereas in the presence of oxalic acid Al, Fe, and Mg were released preferentially relative to Si. In the presence of citric acid, Fe is released preferentially relative to Si. The alteration of chlorites in soils and the amount of released elements into the soil solution therefore depends on the composition of acidifying agents in soils.

Perennial grass growth forms the basis of beef production systems in northern Australia. To improve pasture productivity the woody legume Stylosanthes has been introduced into these native pastures. However, the growth of legumes has been recognised to be a major factor in soil acidification, thereby reducing soil fertility. In order to determine impacts of Stylosanthes scabra (stylo) or Urochloa mosambicensis (urochloa) residues on soil pH, acid neutralising capacity (ANC), and C and N mineralisation, their tops and roots were incubated at a rate equivalent to 10 t dry matter/ha at 25°C for 25 days in topsoil samples of a Mottled-Subnatric Yellow Sodosol from a long-term field experiment under urochloa or under stylo cover. The amount of C[O.sub.2]-C released during the first 2 days of incubation was correlated with the decrease in dissolved organic C. Plant material addition immediately raised the pH and ANC relative to the control. This was related to the amount of ash alkalinity of the plant residues added to the soil. Since the ash alkalinity is a measure for the organic anion content of plant material, it was concluded that the pH buffering was due to protonation of organic anions. During incubation, net N mineralisation was only observed in the urochloa soil amended with stylo leaves. In all other treatments, N added in the residues was immobilised by microorganisms due to the high availability of easily degradable C-sources. Consequently, there was no further change in pH or ANC during incubation, since no significant amounts of [H.sup.+] were produced or consumed during N conversion processes. Additional keywords: ash alkalinity, C:N ratio, DOC, nitrification, soil acidification, organic anions/base cations., Introduction Perennial grass growth forms the basis of beef production systems in northern Australia. Stylosanthes (stylo), a tropical woody legume shrub, has been introduced into these native pastures in order [...]

In the analysis of tert-butyldimethylsilyl derivatives (TBDMS) of alkyl methylphosphonic acids (RMPA) and methylphosphonic acid (MPA), from soils by gas chromatography/mass spectrometry (GC/MS), the detection yields are generally low, due to the suppression of TBDMS derivatization by the soil matrix components and the adsorption of RMPA and MPA to the soils. An ion-exchange pretreatment of the aqueous soil extract can be used to overcome the former factor by removing interfering compounds. A pretreatment method is described for improving the detection yields due to the latter factor, using an alkaline extraction procedure. The recovery was estimated quantitatively using capillary electrophoresis. The soil samples tested included volcanogenous immature soils and showed a low aqueous extraction recovery and GC/MS detection yields. The inclusion of sodium hydroxide in the extraction solvent dramatically increased the recovery. Using a 0.1 M sodium hydroxide solution, the recovery was in excess of 68%. Interfering components were removed from the alkaline soil extract by solid-phase extraction of the acids on a silica-based strong anion exchanger. The alkaline soil extract was neutralized with hydrofluoric acid and applied to the cartridge in the fluoride form. After washing with water, MPA and RMPA could be eluted with methanolic ammonia nearly quantitatively. Using the established pretreatment method, MPA and RMPA were detected from all the soil samples in more than 67% yield.

Research has been conducted on the rhizobial populations. The diversity within these populations investigated along with increasing acidity stress gradients in a Brazilian soil and the distribution of the rhizobial genotypes within these populations are discussed.

Research has been conducted on the denitrifying and dinitrogen-fixing microorganisms' biodiversity. The amplifying segments of genes coding for nitrogenase reductase and for various denitrification steps have been investigated and the total bacterial life in the acid forest soil has been analyzed via the gene segment coding for the 16s rRNA which has been amplified from this soil's DNA by PCR.

Field investigations of Rassam et al. in 2001 have highlighted the effects of infiltration, drainage, and evapotranspiration on the dynamics of water flow and solute transport in acid sulfate (AS) soils. In this work, HYDRUS-2D is adopted as the modeling tool to elucidate the trends observed in that field experiment. Hypothetical simulations have shown that the relative contribution of drains to lowering the water table is significant only when closely spaced drains are installed in coarse textured soils, evapotranspiration being the main driving force in all other cases. AS soils reaction products that are close to a drain are readily transportable during infiltration and early drainage, but those produced farther away from it near the midpoint between drains are only slowly transported during a prolonged drainage process. Simulating the field trial of Rassam et al. has shown that drain depth and evapotranspiration significantly affect solute fluxes exported to the ecosystem. Managing AS soils should target minimal drain depth and density. Partial or full lining of the drains should be considered as a management option for ameliorating the environmental hazards of AS soils. DOI: 10.1061/(ASCE)0733-9437(2002)128:2(107) CE Database keywords: Numerical models; Water flow; Acids; Soils; Drainage.

Drains are introduced into acid sulfate (AS) soils grown to sugar cane to prevent waterlogging and drain runoff water. Drains have the potential to promote deleterious reactions and facilitate the transport of the resulting reaction products into the ecosystem. A field experiment was carried out to investigate the hydrology of an AS soil field and monitor the quality of its drainage water. Results have shown that in such low-conductivity soils, a steep water-table draw-down occurs close to the drain. Farther away from the drain, water-table dynamics are predominantly driven by evapotranspiration. The concentration of sulfate ions in the drainage water showed a steep decline during infiltration followed by a moderate surge during drainage. A laboratory leaching column experiment has revealed an increasing sulfate concentration away from the drain. The column experiment confirmed earlier findings of Rassam and Cook, who conducted hypothetical numerical simulations and showed that solutes from low-conductivity AS soils are mainly leached from soils located close to the drain. DOI: 10.1061/(ASCE)0733-9437(2002)128:2(100) CE Database keywords: Drainage; Soils; Acids; Environmental issues; Agricultural wastes.

Electron spin resonance spectroscopy and nuclear magnetic resonance studies indicate that under acidic pH humic substances reduce vanadium (V) to vanadium (IV), with the vanadium(IV) ion bound to the oxygen donor at the carboxylic acid sites of the humic substances. At neutral pH, vanadate is stabilized with its binding to humic substances. The binding of vanadium to humic substances is determined by the concentration of vanadium and the pH of the medium.

The effects of soil acidity on rates of nitrogen release from various ureaform fractions are discussed. The cold water soluble, hot water soluble and the soluble in hotwater but not cold water fractions of a ureaform were analyzed of nitrogen content. Fitting linear increase and plateau models estimated the rate of nitrogen release. Adjustments in rates of applications were found to be necessary for the successful use of ureaform fertilizers.

A test experiment involving the the relative effects of acidity and ionic strength on the chemistry of leachates from fresh, intact forest floor covers is discussed. Acidic and nonacidic treatments were conducted at each concentration. The chemical composition of field-extracted soil solutions were compared with laboratory leachates. Results indicate that the ionic strength ofincoming leaching water determined the downward movement of acidity in soils.

The influence of solution acidity and concentration on ion transport in an allophanic Andisol under saturated and unsaturated conditions is discussed. Anion-exchange capacity, cation-exchange capacity and the exchange isotherms were measured under different acidity conditions and concentrations. The resulting measurements were compared with breakthrough curves. The effect of both solution parameters were found to be significant.

Acid-subsoil amelioration is complicated by differences in the efficacy of lime and gypsum across the diverse soil environments in which the problem occurs. This study was conducted to explain long-term growth responses to lime and gypsum on a Plinthic Paleudult of mixed clay mineralogy. In a 10-season experiment that monitored treatment effects on profile chemical properties, we compared the effects of (i) incorporating 15 Mg [ha.sup.-1] of lime to different depths, (ii) incorporating 25 Mg [ha.sup.-1] of lime to about 0.5 m, and (iii) conventionally incorporating 15 Mg [ha.sup.-1] of lime plus 10 Mg [ha.sup.-1] of gypsum. Even at the highest application rate, lime had minimal effects on acidity below the depth of incorporation. Gypsum, however, markedly improved the rooting environment to a depth of 0.75 m. Sulfate sorption against extraction with dilute Ca[Cl.sub.2] was accompanied by [pH.sub.w] increases of [approximately equals] 0.4 units, by similar increases in [Delta]pH ([pH.sub.w] - [pH.sub.s]), by depressions in exchangeable acidity of as much as 1.5 [cmol.sub.c] [L.sup.-1], and by decreases in acid saturation of more than 30%. The rate of subsoil amelioration was, however, much slower than that reported in more intensely weathered soils of similar texture. Only in the sixth season were benefits evident in the 0.60- to 0.75-m horizon, and acidity in the 0.75- to 0.90-m horizon actually increased significantly. It is speculated that this resulted from N[O.sub.3] accumulation and ionic strength-induced dissolution of interlayer Al. These findings indicate that acid-subsoil amelioration in soils with Al-hydroxy-interlayer minerals requires greater quantities of gypsum than soils that are dominantly kaolinitic.

Abstract It is well established that in the moderately acidic soils of southern Australia, the 0-2 cm layer commonly has a higher pH than soil layers between 2 and 10 [...]