Parent Material Properties Research Articles

Is parent material an important factor in soil carbon and nitrogen mineralization?

Conversion of rocks and organic inputs to parent material and soil is a dynamic process controlled by physical, chemical and biological factors. Soil samples were taken from different parent materials (gypsum, marl and serpentine) in Ankara, Turkey to observe how the properties of parent material reflect on some soil characteristics. Their carbon (C) and nitrogen (N) mineralization were respectively determined by CO2 respiration method and the Parnas-Wagner method under the controlled laboratory conditions for 42 days (28 °C, 80% of field capacity). Soil CO2 respiration showed that there were significant differences between each parent material after 42 days of incubation as following: marl > gypsum > serpentine. Soil C mineralization rate in marl was the highest among the other two soils. NH4-N contents and net N mineralization of soils were significantly highest at the 11th day compared to 26th and 42nd days in all soil types (P < 0.05). NO3-N contents were statistically different from each other in the serpentine soil at all of three times (P < 0.05). Generally, no significant differences were found between soils in all N mineralization parameters in each time of incubation. Our findings showed that soil carbon mineralization was affected by the differences in parent materials, their physical and chemical properties such as texture, pH, CaCO3, C and N contents. It can be concluded that response of soil microorganisms in carbon mineralization is more active than in nitrogen mineralization in all soil types due to a low nitrogen content.

On the interaction between welding residual stresses: A numerical and experimental investigation

The interaction of weld induced residual stresses is an important issue for multi-pass and repair welding operations; effective prediction of the magnitude and location of peak residual stresses can lead to improved lifing predictions and greater understanding of the performance of components in service; however, the interaction of existing residual stress field with new ones imposed by fusion welding processes has received little attention to date. This study presents a numerical and experimental investigation into the interaction of bead-on-plate welds in thick plates of IN718 with the aim of evaluating the effects of pre-existing weld residual stresses on the final global residual stress distribution. Sequentially coupled thermo-mechanical finite element (FE) models, which have been validated through temperature measurements, optical macrography and residual stress measurements, performed using the neutron diffraction technique, have been used to investigate the interactions. The results show good correlation between the experimental and model residual stress fields, demonstrating that the FE models are capable of predicting the redistribution of existing residual stress fields subjected to fusion welding processes and that this can be achieved with the use of parent material properties throughout, without considering any material property modifications which may occur due to microstructural changes in and around the weld region. It can also be seen from the results that, even with the relatively thick plates used in the study, a plane-stress state exists in the plates with a normal stress of approximately zero in all cases.

Evaluation of surface integrity of WEDM processed inconel 718 for jet engine application

A unique superalloy, Inconel 718 has been serving for aerospace industries since last two decades. Due to its attractive properties such as high strength at elevated temperature, improved corrosion and oxidation resistance, it is widely employed in the manufacturing of jet engine components. These components require complex shape without affecting the parent material properties. Traditional machining methods seem to be ineffective to fulfil the demand of aircraft industries. Therefore, an advanced feature of wire electrical discharge machining (WEDM) has been utilized to improve the surface features of the jet engine components. With the help of trim-offset technology, it became possible to achieve considerable amount of residual stresses, lower peak to valley height, reduced density of craters and micro globules, minimum hardness alteration and negligible recast layer formation.

The influence of cattle grazing on methane fluxes and engaged microbial communities in alpine forest soils.

Recent dynamics and uncertainties in global methane budgets necessitate a dissemination of current knowledge on the controls of sources and sinks of atmospheric methane. Forest soils are considered to be efficient methane sinks; however, as they are microbially mediated they are sensitive to anthropogenic influences and tend to switch from being sinks to being methane sources. With regard to global changes in land use, the present study aimed at (i) investigating the influence of grazing on flux rates of methane in forest soils, (ii) deducing possible (a)biotic factors regulating these fluxes, and (iii) gaining an insight into the complex interactions between methane-cycling microorganisms and ecosystem functioning. Here we show that extensive grazing significantly mitigated the soil's sink strength for atmospheric methane through alterations of both microbial activity and community composition. In situ flux measurements revealed that all native, non-grazed areas were net methane consumers, while the adjacent, grazed areas were net methane producers. Whereas neither parent material nor soil properties including moisture and organic matter showed any correlation to the ascertained fluxes, significantly higher archaeal abundances at the grazed study sites indicated that small inputs of methanogens associated with cattle grazing may be sufficient to sustainably increase methane emissions.

THERMOPHYSICAL PROPERTIES OF 904L AUSTENITIC STEEL

This paper presents the results of the structural investigations and thermophysical properties of 904L steel parent material. Experimental studies on the structure of 904L steel proved a pure austenitic structure. Both the experimental research and analysis of the thermophysical properties of 904L steel were complemented with the results of the thermal conductivity calculations for the tested material. The paper presents a brief description of the measurements, the procedures for evaluating the data, and a set of the obtained results.

Flax fiber-reinforced composite lattice cores: A low-cost and recyclable approach

Lightweight, low cost, and recyclability are priorities in various material selections. In this study, flax fiber-reinforced lattice cores with redesigned lattice geometry were developed and manufactured by vacuum-assisted resin infusion and slot assembly method. An orthotropic constitutive model of the redesigned lattice cores was proposed, and the elastic compliance matrix was expressed with lattice geometry and properties of parent materials. Then, lattice structures with composites and foam sandwich trusses were fabricated and compressed, respectively. Specific nominal stiffness and strength values of the latter were approximately 1.5× and 2× those of their monolithic counterparts. Subsequently, mechanical property sensitivity of defects formed during processing was simulated, and the results provided additional insights to optimize the lattice design. A property-cost chart was specially created, and flax fiber-reinforced lattice cores proved to be promising candidates for automotive lightweight industry because of their economy and recyclability.

Relationship between Soil Properties and Plant Diversity in Semiarid Grassland

In ecological studies, soil-plant interaction is an important environmental factor. Soil chemical and physical properties affect plant richness and diversity. This study was carried out to investigate the relationship between soil physical and chemical properties, and plant diversity indexes (Shannon-Weiner and Simpson) in semiarid grassland. Plant diversity indexes and soil properties were determined using 34 quadrats (5x5m) on different parent materials (chrome, marble, serpentine, red chalk and red chalk mostra) in semiarid grasslands in the Central Anatolia Region in Turkey. Plant samples were collected and recorded periodically from April to September (the vegetation period) in 2014 for each quadrat. In order to determine the plant richness and diversity indexes, 3 sub-quadrats (1x1m) were randomly added into each of 34 (5x5 m) quadrats. To evaluate the relationship between plant diversity indexes and soil properties, composite soil samples were collected from the four corners, and the center of each quadrat 0-30 cm in depth, and which was mixing of those subsamples. Soil sand-silt-clay contents, soil reaction (pH), bulk density (BD), electrical conductivity (EC), CaCO3 and soil organic matter (SOM) contents were measured. Relationship between plant diversity indexes measured in different months during vegetation period and soil properties of different parent material was statistically analysed using correlation analysis in SPSS 20.0. Modest correlation coefficient was found between the Simpson diversity index and SOM content, sand-silt-clay content, pH and EC for different months in vegetation period.

Comparison of Parent and Butt-Fusion Material Properties of Unimodal High-Density Polyethylene

The U.S. nuclear power industry is seeking U.S. Nuclear Regulatory Commission (USNRC) approval to use high-density polyethylene (HDPE) in safety-related applications. The USNRC had granted approval for the use of HDPE for safety-related service water applications, with limitations, to Catawba (Duke Energy Corp., Catawba, SC) and Callaway (Union Electric Co., Callaway, MO) based on separate relief requests submitted by the licensees. The nuclear industry continues to show increasing interest in utilizing HDPE in safety-related piping systems. In order to evaluate and maintain the structural integrity of HDPE pipes, the material properties and the fracture resistance behavior must be fully characterized. Although there has been extensive work on material property development of HDPE, most of the investigations have been focused on the parent (base) material. Hence, the material property and fracture resistance behavior of the butt-fusion region have not been comprehensively investigated. In this paper, tensile, dynamic mechanical analysis (DMA), and slow crack growth (SCG) tests were performed for unimodal PE 4710 HDPE material. Specimens were machined from both parent piping material and butt-fusion regions. The test results indicate that the tensile and DMA properties show no significant differences between parent and butt-fusion joint materials. However, in terms of SCG resistance, the time to failure for butt-fusion joint material was an order of magnitude lower than that of the parent material.

Prediction of Distribution of Soil Cd Concentrations in Guangdong Province, China

Heavy metals are one of the principal soil pollution sources. Contaminated soils affect the quality of agricultural products, and then threaten human health. Prediction of the contaminants distribution in the soil is the foundation of pollution evaluation and risk control. A total of 1000 soil profiles were collected to investigate the spatial variation of soil cadmium (Cd) concentration in Guangdong province. These datasets were divided into two groups, about 900 samples for model training and the other 100 for model validation. Six frequently used GIS spatial interpolation methods including Spline, Natural Neighbor, Ordinary Kriging, Inverse Distance Weighted, Local Polynomial Interpolation and Radial Basis Function, and Cubist which is a type of rule-based model were compared to determine their suitability parameters for estimating soil Cd concentration. Nine different resolutions including 2000, 1500, 1000, 800, 500, 300, 200, 150, and 90 m were selected to calculate, evaluate and compare their accuracy. The results showed that, 1 Quantitative assessment of the continuous surfaces showed that there was a large difference in the accuracy of the seven methods. Cubist was superior to GIS-based spatial interpolation methods at all resolutions. Cubist was the best tool for mapping the spatial distribution of Cd in soils with thirty-seven specific predictors relevant to the source and behavior of Cd (parent material, land use, soil type, soil properties, population density, gross domestic product per capita, and the lengths and classes of the roads surrounding the sampling sites, climatic factors, etc.) at 300 m×300 m resolution. The second was Spline, its accuracy was optimal at the 1500 m×1500 m resolution. 2 Results of Cubist suggested that the soil Cd spatial distribution was primarily dependent on the properties of soil regional parent materials. And soil samples with higher Cd concentration mainly located in Carboniferous and Quaternary areas. 3 Spatially, Cd concentrations were higher in the Pearl River Delta region and north of Guangdong Province. Many hotspots existed throughout the Pearl River Delta region due to transportation and pollution of the river. The major anthropogenic inputs of heavy metals to soils and the environment were metalliferous mining and smelting in the north of Guangdong Province. The soil Cd geometric mean concentration of 0.147 mg·kg-1 was lower than that of China, however it varied from zero to 6.056 mg·kg-1. The areas with soil Cd concentrations greater than 1.0 and 3.0 mg·kg-1 were 160 km2 and 2140 km2 respectively, accounting for 0.09% and 1.18% of the total area of Guangdong Province.

Soil parent material-A major driver of plant nutrient limitations in terrestrial ecosystems.

Because the capability of terrestrial ecosystems to fix carbon is constrained by nutrient availability, understanding how nutrients limit plant growth is a key contemporary question. However, what drives nutrient limitations at global scale remains to be clarified. Using global data on plant growth, plant nutritive status, and soil fertility, we investigated to which extent soil parent materials explain nutrient limitations. We found that N limitation was not linked to soil parent materials, but was best explained by climate: ecosystems under harsh (i.e., cold and or dry) climates were more N-limited than ecosystems under more favourable climates. Contrary to N limitation, P limitation was not driven by climate, but by soil parent materials. The influence of soil parent materials was the result of the tight link between actual P pools of soils and physical-chemical properties (acidity, P richness) of soil parent materials. Some other ground-related factors (i.e., soil weathering stage, landform) had a noticeable influence on P limitation, but their role appeared to be relatively smaller than that of geology. The relative importance of N limitation versus P limitation was explained by a combination of climate and soil parent material: at global scale, N limitation became prominent with increasing climatic constraints, but this global trend was modulated at lower scales by the effect of parent materials on P limitation, particularly under climates favourable to biological activity. As compared with soil parent materials, atmospheric deposition had only a weak influence on the global distribution of actual nutrient limitation. Our work advances our understanding of the distribution of nutrient limitation at global scale. In particular, it stresses the need to take soil parent materials into account when investigating plant growth response to environment changes.

Evaluating SoilGen2 as a tool for projecting soil evolution induced by global change

To protect soils against threats, it is necessary to predict the consequences of human activities and global change on their evolution on a ten to hundred year time scale. Mechanistic modelling of soil evolution is then a useful tool. We analysed the ability of the SoilGen model to be used for projections of soil characteristics associated to various soil threats: vertical distributions of <2μm fraction, organic carbon content (OC), bulk density and pH. This analysis took the form of a functional sensitivity analysis in which we varied the initial conditions (parent material properties) and boundary conditions (co-evolution of precipitation and temperature; type and amount of fertilization and tillage as well as duration of agriculture). The simulated scenario variants comprised anthroposequences in Luvisols at two sites with one default scenario, six variants for initial conditions and 12 variants for boundary conditions. The variants reflect the uncertainties to our knowledge of parent material properties or reconstructed boundary conditions.We demonstrated a sensitivity of the model to climate and agricultural practices for all properties. We also conclude that final model results are not significantly affected by the uncertainties of boundary conditions for long simulations runs, although influenced by uncertainties on initial conditions.The best results were for organic carbon, although improvements can be reached through calibration or by incorporating a dynamic vegetation growth module in SoilGen. Results were poor for bulk density due to a fixed-volume assumption in the model, which is not easily modified. The <2μm fraction depth patterns are reasonable but the process of clay new formation needs to be added to obtain the belly shape of the Bt horizon.After calibration for organic carbon under agriculture, the model is suitable for producing soil projections due to global change.

Parent material influence on soil response to vegetation change, Southeastern Minnesota, U.S.A.

Soil morphology changes dramatically across the former transition from forest to grassland in the Midwestern U.S.A. That vegetation boundary shifted as a result of Holocene climatic change and fire suppression following Euroamerican settlement, but the timescale of soil response to those vegetation changes and the factors that influence it are poorly known. On steep colluvial slopes of southeastern Minnesota, Mollisols with thick, dark A horizons typically associated with grassland are found today under deciduous forest. Soils with much thinner and/or lighter-colored A horizons occur immediately up- and downslope of the forest-covered Mollisols. Most of the soils with thick A horizons are not in topographic settings found to favor organic matter accumulation in other landscapes. Principal component analysis highlights important axes of textural and mineralogical variation among horizons of these soils, often related to parent material properties. Soils with and without thick A horizons are separated along one principal component heavily loaded by high pH, reflecting the presence of dolomite fragments in the hillslope sediment that soils with thick, dark A horizons formed in. Stable C isotope analysis reveals that the Mollisols with thick, dark A horizons under forest had C input from vegetation with abundant C4 grasses in the past. Public land survey data also indicate replacement of grassland or savanna by forest since 1854 on colluvial slopes where forest-covered Mollisols occur today. We propose that the soils with thick, dark A horizons under forest today reflect a lagged response to vegetation change, from grassland or savanna to closed forest. Their thick A horizons and some C4-derived organic matter may be preserved because dolomite weathering releases abundant Ca++ and Mg++ that favor aggregation and organic matter stabilization. Soils with thin A horizons just up- or downslope may also have formed partly under grasses, but have responded more quickly and/or more substantially to vegetation change.

INFLUENCE OF LITHO-MORPHOGENETIC, HYDROLOGIC AND ANTHROPOGENIC FACTORS ON SORPTIVE AND BUFFER PROPERTIES OF SOILS OF EROSIONAL-DENUDATIONAL VALLEYS: CASE STUDY FROM SŁAWIEŃSKA PLAIN

The aim of the study has been to assess the role of litho-morphogenetic, hydrologic and anthropogenic factors influencing spatial variability of sorptive and buffer properties of the soils of erosional-denudational valley incised in hollow sediments flat-dipping glacial till in the area of Slawienska Plain. Parent material properties, water - as a causative agent of erosion and ions carrier, as well as the quantity and the properties of organic matter were basic factors influencing spatial variability of sorptive and buffer properties of the examined soils. The sorption capacity of Stagnic Dystric Cambisols of the high plain formed of strongly acid, silt-clay hollow sediments ranged from 8.74 to 22.12 cmol(+) kg-1. Acidic cations dominated in the sorption complex of the soils, but its percentage decreased with depth. Colluvic Regosols of the slopes had a lower content of clay and organic matter in relation to the soils of the high plain which was reflected in a lower sorption capacity. The cation exchange capacity of Colluvic Gleysols and Mollic Gleysols of the bottom of the valley ranged from 7.21 to 25.68 cmol(+) kg-1 and was positively related to the content of soil organic matter and clay. The high base saturation of the soils (97.2–100.0%) was an effect of the influence of supplying water. Calcium dominated among base cations. The soils of the high plain and slopes had high buffering capacity of basis and low of acids. Higher buffering capacity of acids found in the soils of the valley bottom was an effect of almost full saturation of soil sorption complex with exchangeable basis.

Effect of Welding Thermal Cycles on Microstructure and Mechanical Properties of Simulated Heat Affected Zone for a Weldox 1300 Ultra-High Strength Alloy Steel

In the present study, the investigation of weldability of ultra-high strength steel has been presented. The thermal simulated samples were used to investigate the effect of welding cooling time t8/5 on microstructure and mechanical properties of heat affected zone (HAZ) for a Weldox 1300 ultra-high strength steel. In the frame of these investigation the microstructure was studied by light and transmission electron microscopies. Mechanical properties of parent material were analysed by tensile, impact and hardness tests. In details the influence of cooling time in the range of 2,5 ÷ 300 sec. on hardness, impact toughness and microstructure of simulated HAZ was studied by using welding thermal simulation test. The microstructure of ultra-high strength steel is mainly composed of tempered martensite. The results show that the impact toughness and hardness decrease with increase of t8/5 under condition of a single thermal cycle in simulated HAZ. The increase of cooling time to 300 s causes that the microstructure consists of ferrite and bainite mixture. Lower hardness, for t8/5 ≥ 60 s indicated that low risk of cold cracking in HAZ for longer cooling time, exists.

A New Approach to the Land Capability Classification: Case Study of Turkey

Land capability classification is one of the very important issues in terms of sustainable land use. Many land capability classifications have been prepared and applied especially in the developed countries such as USA, UK and France. Most of the land capability classification systems and mapping are an adaptation of the US Department of Agriculture method. Up to now the criteria that are taken into consideration in the land capability classification are topography especially inclination of slope and soil properties, in general. In a mountainous country or regions topographic-geomorphic unites, climate and parent material are factors that must be taken into consideration in order to establish land capability classification. All these criteria are used in this study. The aim of this study is to reestablish a land classification according to the geomorphic units, climate and parent material factors in Turkey. According to these criteria, seven land capability classes were determined. Moreover, the subclass are identified according the parent material properties that mostly outcropped on the mountainous areas.

IDENTIFICATION OF THE HYDROGEOCHEMICAL PROCESSES IN GROUNDWATER OF GLEYSOLS AND RETISOLS TOPOSEQUENCE OF THE OPALENICA PLAIN

Hydrogeochemical investigation was carried out in the toposequence of Gleysols and Retisols within the Opalenica Plain. Groundwater samples from the study area were collected every two or four weeks from 2002 to 2006 in pre-cleaned 1-L polyethylene bottle from 2 representative wells. The results of research indicated that the quantity of dissolved components in groundwater was connected with wells location in the relief and the properties of soil parent materials. The groundwater of soil located higher in the slope (Retisols) was characterized by smaller concentrations of the analysed components, when compared with the composition of groundwater from lower sites of the slope (Gleysols). The groundwater chemistry is mainly controlled by weathering of carbonate minerals as well as silicate weathering. Moreover, the research results indicate that evaporation process can influence the chemical composition of groundwater in the lower part of the slope.

Ground State Reactions of nC60 with Free Chlorine in Water.

Facile, photoenhanced transformations of water-stable C60 aggregates (nC60) to oxidized, soluble fullerene derivatives, have been described as key processes in understanding the ultimate environmental fate of fullerene based materials. In contrast, fewer studies have evaluated the aqueous reactivity of nC60 during ground-state conditions (i.e., dark conditions). Herein, this study identifies and characterizes the physicochemical transformations of C60 (as nC60 suspensions) in the presence of free chlorine, a globally used chemical oxidant, in the absence of light under environmentally relevant conditions. Results show that nC60 undergoes significant oxidation in the presence of free chlorine and the oxidation reaction rates increase with free chlorine concentration while being inversely related to solution pH. Product characterization by FTIR, XPS, Raman Spectroscopy, TEM, XRD, TOC, collectively demonstrates that oxidized C60 derivatives are readily formed in the presence of free chlorine with extensive covalent oxygen and even chlorine additions, and behave as soft (or loose) clusters in solution. Aggregation kinetics, as a function of pH and ionic strength/type, show a significant increase in product stabilities for all cases evaluated, even at pH values approaching 1. As expected with increased (surface) oxidation, classic Kow partitioning studies indicate that product clusters are relatively more hydrophilic than parent (reactant) nC60. Taken together, this work highlights the importance of understanding nanomaterial reactivity and the identification of corresponding stable daughter products, which are likely to differ significantly from parent material properties and behaviors.

Tree or soil? Factors influencing humus form differentiation in Italian forests

We aim to investigate the occurrence of forest humus forms (Moder, Amphi and Mull) in relation to environmental factors describing parent material, climate and tree species. Boosted regression trees (BRTs) were applied as modeling tool to analyze data of 238 plots of the BioSoil database covering the whole Italian forest territory. Though predictive ability was not very high, especially for the Amphi form, we could gain significant insight into factors controlling humus form differentiation. In the BRT analysis, the diversity of tree species was the most important predictor for Moder and Mull models and specific plant effects were evidenced. However, our results showed that the geographic distribution of Italian forest species was influenced by soil and climate conditions, partly explaining the high weight of tree species as factor. The importance of the soil nutritional status, due to parent material properties, in driving humus form differentiation was stated, highlighting the key role played by pH and calcium content, with the hitherto understated importance of phosphorus. This study further clarified the functioning of the still poorly understood Amphi form. Reduced effective soil volume (EfVol) combined with seasonality appeared to constrain pedofauna activity in otherwise favorable and nutrient rich systems, favoring the evolution of Amphi instead of Mull forms.

Fabric and properties of mineral soils underlying a shallow peat mantle in Estonia

The morphology and chemical characteristics of mineral soils underlying modern peaty (histic) and shallow peat soils (or histosols) are analyzed in pedoecological conditions of Estonia. The underlying shallow peat mantle gley soils have been formed on different geological origin (glaciolacustrine, glacial, glaciofluvial, marine) parent materials. The peat mantle overlying gley soils has accumulated in the process of landscape paludification during the post glacial period. Using the Estonian Soil Classification (ESC), the peat layer thickness of peaty soils is 10–30 cm and of shallow peat soils, 30–100 cm. The studied peaty soils may be characterized as polygenetic soils. Depending on parent material properties (calcareousness, acidity, texture) and feeding water the peaty soils are divided into two types specified by ESC as peaty gley soils and peaty podzols, and by WRB as Histic Gleysols and Histic Podzols. The mineral soils underlying peat soils may be defined as paleosols. The development of such soils has proceeded according to the chronosequence: gley soils or protosols → peaty soils → fen soils → transitional bog soils → bog soils, whereas mineral paleosols may be found under fen, transitional bog and bog soils. The peat soils studied in this research work, classified by ESC as drained shallow transitional (mesotrophic) bog soils and by WRB as Drainic Dystric Ombric Hemic Fibric Histosols, are located on the edges of bog areas and are fed mostly by mesotrophic surface seepage water. In comparative analysis of three soil groups (peaty gley soils, peaty podzols and shallow peat soils) (i) their location on the landscape, the geological origin of their parent materials and morphology of the mineral layers are characterized; (ii) the vertical distribution of organic carbon and total nitrogen contents, and different characteristics of soil acidity are analyzed, and (iii) their catenal position or associated soils are characterized. In the case of peaty soils, the three types of mineral soil profiles (eluvial, eluvio-accumulative and accumulative) which underlie the peat cover were elucidated. Under thicker peat layers, i.e. under shallow peat soils, mostly humus accumulative profiles were found. In all analyzed sites, in the course of progressive paludification (among this peatification) the peaty soils have been formed from gley soils. The formation of the peaty soil stage was followed by the fen soil stage. Depending on the feeding water, some of these soils developed in the direction of bog soils, with an intermediary transitional bog stage. Artificial drainage is of great importance in the development of peat cover, which influences first the decomposition of top layer peat.

Phosphorus sorption, supply potential and availability in soils with contrasting parent material and soil chemical properties

SummarySoil phosphorus (P) management requires a more targeted and soil‐specific approach than is currently applied for agronomic recommendations and environmental evaluation. Phosphorus buffering capacities control the supply of P in the soil solution and were measured across Irish soils with contrasting parent material and chemical properties. Langmuir sorption buffer capacities (MBCs) and binding energies (b) were strongly correlated with soil pH and extractable aluminium (Al). A broken‐line regression fitted to the relationship between MBC and Al derived a change‐point value for Al above which MBC increased linearly. Soils above the change point were predominantly acidic to neutral with non‐calcareous parent material, with larger buffering capacities and binding energies than calcareous soils. Ratios of Mehlich3‐Al and P (Al:P) were used to relate buffering capacity to supply potential in non‐calcareous soils. Large ratios of Al:P were associated with poor P availability, characteristic of strongly P‐fixing soils. Threshold values of iron‐oxide paper strip P (FeO‐P) and Morgan's P revealed Al:P ratios where soils began to supply P in available form. The change‐point for Morgan's P fell within the current target index for P availability; however, the confidence interval was more compatible with previous agronomic P indices used in Ireland. Relationships between Morgan's P and measures of extractable P, M3‐P and Olsen P, deviated in calcareous soils at large soil P contents, indicative of P precipitation processes dominating in these soils. Identifying differences in soil P buffering capacity at the laboratory scale would improve agronomic and environmental assessment at field and catchment scales.