Alex B Mcbratney

• FAA PhD DSc DScAgr
• Managing Director at The University of Sydney

While global efforts to operationalise soil spectroscopy are progressing, cooperation is needed to fully its potential for generating digital soil information to support sustainable soil management worldwide. The Global Soil Laboratory Network's soil spectroscopy initiative (GLOSOLAN-Spec), led by the Food and Agriculture Organization of the United...

Understanding the presence and dynamics of soil inorganic carbon (SIC) is essential, given its role as a significant sink for atmospheric carbon within the global carbon cycle. In arid and semi-arid regions such as Australia, soils may contain a higher proportion of SIC compared to soil organic carbon (SOC). However, the relative magnitudes of SIC...

The Soil and Landscape Grid of Australia (SLGA) has been significantly updated and expanded. The initial version, released in 2015, provided the first continental-scale characterization of soil resources adhering to GlobalSoilMap specifications. It featured digital maps for 11 key soil attributes (including bulk density, organic carbon, soil textur...

Soil organic carbon (SOC) plays a critical role in key soil functions, yet SOC is highly vulnerable to human activities, which can shift soil from acting as a net carbon sink to becoming a net carbon source. Despite considerable efforts to monitor soil conditions , traditional evaluations often focus on temporal comparisons within similar locations...

Soil is a highly diverse natural resource crucial for the functioning of ecosystems and essential for ensuring food security, biodiversity, water quality, and climate regulation. Despite its significance, soil faces increasing degradation pressures from agriculture, urbanisation, and climate change. Previous work has classified soil into pedogenons...

Uncertainty quantification is a crucial step for the practical application of soil spectral models, particularly in supporting real-world decision making and risk assessment. While machine learning has made remarkable strides in predicting various physiochemical properties of soils using spectroscopy, predictions devoid of quantified uncertainty of...

Despite the critical role of soil microbial communities in biomass production and ecosystem functioning, previous research primarily focussed on microbial structure without functional insights, especially for rare species. This study addresses this gap by exploring the functional potential of both abundant and rare bacterial communities across vari...

Machine learning (ML) applications in soil science have significantly increased over the past two decades, reflecting a growing trend towards data-driven research addressing soil security. This extensive application has mainly focused on enhancing predictions of soil properties, particularly soil organic carbon, and improving the accuracy of digita...

Soil provides multiple and diverse functions (e.g., the provision of food and the regulation of carbon), which underpin the health of animals, humans, the environment and the planet. However, the world’s soils face existential challenges. To this end, the concept of Soil Security was developed, compelled to: “maintain and improve soils worldwide so...

Advancing the use of X-ray fluorescence (XRF) as an accessible tool for monitoring soil fertility requires an understanding of how the temporal dynamics of the ratio between total and plant-available content (T/A ratio) affects the performance of models for plant-available nutrients prediction. This study assesses the stability of XRF models in pre...

The crucial role of soil in global food production and its multifaceted contributions to ecosystem services underscore the need for a comprehensive evaluation framework. This study presents a novel approach to soil evaluation by integrating the assessment of soil functions, services, and threats into a unified metric which quantifies the capital di...

The mapping of soils in Africa is at least a century old. We currently have access to various maps depicting mapping units locally and for the continent. In the past two decades, there has been a growing interest in alternatives for generating soil maps through digital soil mapping (DSM) techniques. There are, however, numerous challenges pertainin...

In flooded paddy fields, peak greenhouse gas nitrous oxide (N2O) emission after rewetting the dry soils is widely recognised. However, the relative contribution of biotic and abiotic factors to this emission remains uncertain. In this study, we used the isotope technique (δ¹⁸O and δ¹⁵NSP) and molecular-based microbial analysis in an anoxic incubati...

The quest for a global soil classification system has been a long-standing challenge in soil science. There currently exist two, seemingly disjoint, global soil classification systems, the USDA Soil Taxonomy and the World Reference Base for Soil Resources, and many regional and national systems. While both systems are acknowledged as international,...

Aggregation is one of the key properties influencing the function of soils, including the soil’s potential to stabilise organic carbon and create habitats for micro-organisms. The mechanisms by which organic matter influences aggregation and alters the pore geometry remain largely unknown. We hypothesised that rapid microbial processing of organic...

Context The Tea Bag Index (TBI) evaluates the rate of organic matter decomposition using Lipton tea bags. However, this tea bag cannot be easily found in Australia, having to be imported from Europe. The 90-day incubation period also poses problems for school and citizen science projects, such as missing tea bags and organism-induced damage. Aims...

Soil microbial diversity mediates a wide range of key processes and ecosystem services influencing planetary health. Our knowledge of microbial biogeography patterns, spatial drivers and human impacts at the continental scale remains limited. Here, we reveal the drivers of bacterial and fungal community distribution in Australian topsoils using 138...

The soil security concept has been put forward to maintain and improve soil resources inter alia to provide food, clean water, climate change mitigation and adaptation, and to protect ecosystems. A provisional framework suggested indicators for the soil security dimensions, and a methodology to achieve a quantification. In this study, we illustrate...

Context Legacy data from prior studies enable preliminary analysis for soil security assessment which will inform future research questions. Aims This study aims to utilise the soil security assessment framework (SSAF) to evaluate the capacity of soil in fulfilling various roles and understand the underlying drivers. Methods The framework entails...

Australia is home to a diverse range of unique native fauna and flora. To address whether Australian ecosystems also harbour unique viruses, we performed meta-transcriptomic sequencing of 16 farmland and sediment samples taken from the east and west coasts of Australia. We identified 2460 putatively novel RNA viruses across 18 orders, the vast majo...

Soil is a central component to seven existential challenges humanity currently faces, including food, water and energy security, climate change abatement, biodiversity protection, human health and ecosystem services delivery. Soils, however, are under threat and securing soil has become an eighth existential challenge. Soil security can be understo...

Various machine‐learning models have been extensively applied to predict soil properties using infrared spectroscopy. Beyond the interpretability and transparency of these models, there is an ongoing discussion on the reliability of predictions generated for soil spectra of soil properties. In this review, we contribute to this discussion by advoca...

Australia is home to a diverse range of unique native fauna and flora. To address whether Australian ecosystems also harbour unique viruses, we performed meta-transcriptomic sequencing of 16 farmland and sediment samples taken from the east and west coasts of Australia. We identified 2,562 putatively novel viruses across 15 orders, the vast majorit...

The intensification of human pressures on soil can reduce pedodiversity and decrease soil multifunctionality impacting soil security. Mapping genosoils (least modified soils within a soil class or soil map unit by contemporary drivers of soil change) and phenosoils (variants resulting from land use history and management) can be a preliminary step...

Soil organic carbon (SOC) is the largest terrestrial carbon pool. SOC is composed of a continuous set of compounds with different chemical compositions, origins, and susceptibilities to decomposition that are commonly separated into pools characterised by different responses to anthropogenic and environmental disturbance. Here we map the contributi...

We introduce a new dataset of high-resolution gridded total soil organic carbon content data produced at 30 m × 30 m and 90 m × 90 m resolutions across Australia. For each product resolution, the dataset consists of six maps of soil organic carbon content along with an estimate of the uncertainty represented by the 90% prediction interval. Soil org...

Human societies face six existential challenges to their sustainable development. These challenges have been previously addressed by a myriad of concepts such as soil conservation, soil quality, and soil health. Yet, of these, only soil security attempts to integrate the six existential challenges concurrently through the five biophysical and socio...

Real-time crop canopy nitrogen concentration (CNC) and aboveground biomass (AGB) sensing capability can enable precision agriculture with significant economic and ecological benefits. Canopy spectral response in visible near-infrared (VNIR, 400-979 nm) has been widely used to estimate CNC and AGB of canopies but is often confounded by the soil back...

Participatory approaches to data gathering and research which involve farmers, laypeople, amateur soil scientists, concerned community members or school students have attracted much attention recently, not only to enable scientific progress but also to achieve social and educational outcomes. Non-expert participation in soil research and management...

Soil organic carbon (SOC) storage and redistribution across the landscape (through erosion and deposition) are linked to soil physicochemical properties and can affect soil quality. However, the spatial and temporal variability of soil erosion and SOC remains uncertain. Whether soil redistribution leads to SOC gains or losses continues to be hotly...

Many areas in the world suffer from relatively sparse soil data availability. This results in inefficient implementation of soil-related studies and inadequate recommendations for improving soil management strategies. Commonly, this problem is tackled by collecting new soil data which are used to update legacy soil surveys. New soil data collection...

Soil inorganic carbon (SIC) contributes to up to half of the terrestrial C stock and is especially significant in arid and semi-arid environments, yet has not been explored as much as soil organic carbon (SOC). SIC plays an important role in agriculture, CO2 sequestration and emission and climate regulation. To address this, a comprehensive review...

Soil inorganic carbon (SIC) contributes to up to half of the terrestrial C stock and is especially significant in arid and semi-arid environments, yet has not been explored as much as soil organic carbon (SOC). SIC plays an important role in agriculture, CO2 sequestration and emission and climate regulation. To address this, a comprehensive review...

Microorganisms play pivotal roles in soil processes. Metabolically related microorganisms constitute functional groups, and diverse microbial functional groups control nutrient cycling in soils. This study explored environmental (i.e., rainfall, temperature) and soil factors driving the distribution of bacterial functional groups involved in soil c...

Soil organic carbon (SOC) is the largest terrestrial carbon pool. SOC is composed of a continuum set of compounds 10 with different chemical composition, origin and susceptibilities to decomposition, that are commonly separated into pools characterised by different responses to anthropogenic and environmental disturbance. Here we map the contributi...

Soil organic carbon (SOC) sequestration is the transfer of CO2 from the atmosphere into soil organic matter. It, therefore, relies on photo- synthesis and plant-derived carbon (C) input, which usually occurs through biomass production. Janzen et al. (2022) reminded us that when calculating SOC sequestration potential, we should recognise the source...

Mapping soil classes can support the understanding of soil origin and development, subsequently the soil classes can be used to support monitoring and assessing soil change due to human influence. Pedogenon was proposed as a conceptual soil taxon derived from a set of quantitative state variables representing the soil-forming factors for a given re...

A fifty-four per cent of the global population is estimated to live disconnected from the natural environment. Furthermore, a large majority of our community unknown how significant is the soil in their life, e.g. the provider of food, energy and medicine, etc. Strengthening this connection is one relevant action toward Soil Security, referred to a...

Improving the amount of organic carbon in soils is an attractive alternative to partially mitigate climate change. However, the amount of carbon that can be potentially added to the soil is still being debated, and there is a lack of information on additional storage potential on global cropland. Soil organic carbon (SOC) sequestration potential is...

Since the early 2000s, digital soil maps have been successfully used for various applications, including precision agriculture, environmental assessments and land use management. Globally, however, there are large disparities in the availability of soil data on which digital soil mapping (DSM) models can be fitted. Several studies attempted to tran...

Recent reviews have identified major themes within regenerative agriculture—soil health, biodiversity, and socioeconomic disparities—but have so far been unable to clarify a definition based on practice and/or outcomes. In recent years, the concept has seen a rapid increase in farming, popular, and corporate interest, the scope of which now sees re...

Soils deliver multiple ecosystem services (ES) that are essential for life on Earth, such as – among others - water and climate regulation, nutrient cycling, and biomass production. Understanding society's perception of the benefits provided by soils can provide valuable insights regarding the human-nature relation. However, despite soil's many con...

An increasing number of soil spectral libraries are being developed at larger extents, including at national, continental, and global scales. However, the prediction accuracy of these libraries was often fairly poor when used on local scales. This study evaluates different strategies to improve the model accuracy of a regional spectral library for...

Quantitative assessment of soil functions requires the characterization of soil capability and condition. Mid-infrared (MIR) spectroscopy has been suggested as a viable alternative to the wet chemistry method. However, the extensive set of soil properties that can be well predicted have yet to be explored. The USDA MIR spectral library contains app...

Although soil degradation has become a global phenomenon that might severely threaten the provision of a large range of ecosystem services, not much is known about the economic value of soil functions such as carbon sequestration and rainfall water infiltration. Knowing these values would be an important input into the recently developed concept of...

Not only do soils provide 98.7% of the calories consumed by humans, they also provide numerous other functions upon which planetary survivability closely depends. However, our continuously increasing focus on soils for biomass provision (food, fiber, and energy) through intensive agriculture is rapidly degrading soils and diminishing their capacity...

Soil microbial interactions are crucial in performing ecosystem functions. The microbial co-occurrence network could shed a new understanding of microbial functioning as affected by land management. Current studies on microbial community interactions mainly considered surface soils, thus the understanding of the microbial interactions and functions...

Pedometrics is concerned with the application of mathematical and statistical methods to the study of the distribution and genesis of soils. Here, we describe the main areas that pedometric research addresses: distribution of the soil pattern in character space, spatial and spatio-temporal soil variation, quantitative evaluation of the utility and...

Background and objectives Flour millers often produce several flour types from a single wheat grist. Consequently, different specifications characterize each flour. For example, French standards specify six different flour types, each classified by ash content. The proportional blending of different flour streams from a single wheat grist achieves...

Pedometrics, the application of mathematical and statistical methods to the study of the distribution and genesis of soils, has broadened its scope over the past two decades. The primary focus of pedometricians has traditionally been on spatial and spatio-temporal soil inventories with numerical soil classification, geostatistical modelling of spat...

Soil organic carbon sequestration (SOCseq) is considered the most attractive carbon capture technology to partially mitigate climate change. However, there is conflicting evidence regarding the potential of SOCseq. The additional storage potential on existing global cropland is missing. SOCseq is region-specific and conditioned by management but mo...

Citizen science is becoming a significant contribution to large scale soil surveys. TeaComposition is a citizen science project introducing the Tea Bag Index (TBI) method to students in Australia to support research on soil decomposition using tea bags (green and rooibos). Soil microbial driven decomposition is an essential soil function that relea...

Background and objectives Flour millers are faced with constraints of having to meet proximate specifications, usually defined by supply contracts, while trying to maximise yield. The study investigated the application of response surface methodology (RSM), in a commercial scale flour mill, as a means of maximizing yield while meeting quality const...

Soil ecosystem services (ES) provide multiple benefits to human well-being, but the failure to appreciate them has led to soil degradation issues across the globe. Despite an increasing interest in the threats to soil resources, economic valuation in this context is limited. Importantly, most of the existing valuation studies do not account for the...

While the use of pesticides continues to rise worldwide, our understanding of the pervasiveness of associated contamination and the health risks humans may be exposed to remain limited to small samples size, based on the geographic scales, the exposed population, or the pesticide types. Using our recent mapping of global pesticide use, we quantify...

Digital convergence is helping us to better understand and study the soil. Fixed and mobile sensors, and wireless communication systems aided by the internet produce cheap and abundant streams of digital soil data that can readily be used for modeling and information generation. Here, we explore the ways in which digital science and technology have...

The assessment of changes in soil condition and capability requires the identification of a reference state specific to each soil class. This study develops a framework for mapping soil classes that can be used as a reference state. It identifies soil classes that should have undergone similar historic anthropedogenesis, and differentiate, within e...

Soil is a complex system in which biological, chemical and physical interactions take place. The behaviour of these interactions changes in spatial scale from the atomic to the global, and in time. To understand how this system works, soil scientists usually rely on incremental improvements in the knowledge by refinement of theories through hypothe...

Self-citation is a common practice in soil science publications, but can we find a common behaviour in soil science papers, and are there outliers? Here we investigate self-referencing (referencing earlier papers on which a researcher is an author or co-author) for papers published in nine leading soil science journals (Soil Biology and Biochemistr...

Soil entities are generally defined based on soil properties, using morphological, genetic, or utilitarian criteria. Alternatively, soil entities could be characterized by groupings of homogeneous soil-forming factors under the assumption that the dominant soil-forming processes occurring over a time period within each group are similar, and theref...

In this study, a map of soil parent material is created to support the delineation of soil properties and classes of the Narrabri Shire, NSW. Currently, available information in this study area is geological and lithological maps at a scale of 1:250 000 to 1:1 000 000. These maps are not detailed, and the description in some areas is not accurate....

Pesticides are widely used to protect food production and meet global food demand but are also ubiquitous environmental pollutants, causing adverse effects on water quality, biodiversity and human health. Here we use a global database of pesticide applications and a spatially explicit environmental model to estimate the world geography of environme...

Biochar is recommended as a soil amendment for its positive influence on soil hydrological properties, which results in improved soil fertility and crop yield. Much research in the last decade has been conducted in field and laboratory conditions on the effect of biochar on the hydraulic properties of soil. However, reported results in the literatu...

Soil slaking is a highly relevant property in erosion risk management and soil physics in general. Despite its importance and close relation with known soil chemical and physical properties such as soil organic carbon content, pH, sodium content, and soil aggregate stability, it is still underutilized mainly due to the lack of practical methodologi...

In digital soil spectroscopy, similarity or distance metrics between soil spectra are necessary for a large number of applications, such as for assessing the reliability of a spectrometer over repeated scans, to search for a similar soil sample based on spectra from a large database, to classify spectra into groups of similar characteristics or mor...

Measurement protocols for the same material often vary from laboratory to laboratory. Similarly, while the same spectrometer or sensor can be used between laboratories, the difference in terms of sensor or spectrometer manufacturer is likely to introduce additional variation in the recorded spectrum.

Usually, spectra are obtained for all the soil samples available, but only a subset of these samples are sent to the laboratory for chemical and physical analysis. The reason is that spectra are fast and cheap to retrieve, while a single soil analysis (e.g. for soil clay) is relatively slow, and significantly more costly, to obtain. One must select...

The most common way of estimating soil properties from pre-processed spectra is by calibrating a statistical model. If the response of the spectra at a particular wavelength follows the Beer-Lambert law, the degree of reflectance at a particular wavelength is proportional to the concentration of a soil property. In this case, a linear model can be...

This book provides a didactic overview of techniques for inferring information from soil spectroscopic data, and the codes in the R programming language for performing such analyses. It is intended for students, researchers and practitioners looking to infer soil information from spectroscopic data, focusing mainly on, but not restricted to, the in...

Hypotheses are of major importance in scientific research. In current applications of machine learning algorithms for soil mapping the hypotheses being tested or developed are often ambiguous or undefined. Mapping soil properties or classes, however, does not tell much about the dynamics and processes that underly soil genesis and evolution. When t...

Soil is a three-dimensional volume with property variability in all three dimensions. In Digital Soil Mapping (DSM), the variation of soil properties down a profile is usually harmonised by the use of the equal-area spline depth function approach. Soil observations at various depth intervals are harmonised to predetermined depth intervals. To creat...

There is a growing interest in the use of soil composition as a form of evidence in food provenance, forensics, biosecurity, and archaeology. Given a soil sample of unknown origin, we should like to know the likely geographical source of that material. In this study, we investigated whether data provided from a rapid and non-destructive sensor can...

R provides a convenient and flexible data-analytic environment for soil spectral data. R is a programming language and a software facility for data manipulation, statistical analysis and graphics. R is an implementation of the S language developed at Bell Laboratories (Venables et al. 2009) in the 1980s. While R is an integrated environment for dat...

This chapter describes the datasets and R packages used in the book. A total of five datasets are provided and described. They originate from several studies and are made available through a book-associated R package. Most R functions used in this book are either provided in the text or available online in R packages.

Soil aggregate stability is a useful indicator of soil physical health and can be used to monitor condition through time. A novel method of quantifying soil aggregate stability, based on the relative increase in the footprint area of aggregates as they disintegrate when immersed in water, has been developed and can be performed using a smartphone a...

Digital Soil Mapping and Assessment (DSMA) has progressed from challenging traditional soil science paradigms, through small scale prototyping, to large-scale implementation capturing quantitative measures of soil attributes and functions. This paper considers the future for DSMA in the context of a highly uncertain world where high-quality knowled...

Mapping soil resources at a national scale in large countries such as India is a challenge because of limited soil data available and efforts to collect them. Legacy soil information shows promise; but, there are still challenges that need to be addressed. In this study, we deliver the first digital maps of key soil properties down to 2 m depth acr...

Human disturbances to soils can lead to dramatic changes in soil physical, chemical, and biological properties. The influence of agricultural activities on the bacterial community over different orders of soil and at depth is still not well understood. We used the concept of genoform and phenoform to investigate the vertical (down to 1 m depth) soi...

Soil structure is an important physical property that can be degraded by soil tillage, but methods for quantifying soil structure are both few and time consuming. We developed a method for multistripe laser triangulation (MLT) scanning to quantify soil structure that can be accomplished quickly (15 min of scanning per A horizon exposure) in the fie...

The uptake of machine learning (ML) algorithms in digital soil mapping (DSM) is transforming the way soil scientists produce their maps. Within the past two decades, soil scientists have applied ML to a wide range of scenarios, by mapping soil properties or classes with various ML algorithms, on spatial scale from the local to the global, and with...

Australia has advanced the science and application of Digital Soil Mapping (DSM). Over the past decade, DSM in Australia has evolved from being purely research focused to become 'operational', where it is embedded into many soil-agency land resource assessment programs around the country. This has resulted from a series of 'drivers', such as an inc...