Damien J. Field

Soil Security: Solving the Global Soil Crisis

Soil degradation is a critical and growing global problem. As the world population increases, pressure on soil also increases and the natural capital of soil faces continuing decline. International policy makers have recognized this and a range of initiatives to address it have emerged over recent years. However, a gap remains between what the science tells us about soil and its role in underpinning ecological and human sustainable development, and existing policy instruments for sustainable development. Functioning soil is necessary for ecosystem service delivery, climate change abatement, food and fiber production and fresh water storage. Yet key policy instruments and initiatives for sustainable development have under-recognized the role of soil in addressing major challenges including food and water security, biodiversity loss, climate change and energy sustainability. Soil science has not been sufficiently translated to policy for sustainable development. Two underlying reasons for this are explored and the new concept of soil security is proposed to bridge the science–policy divide. Soil security is explored as a conceptual framework that could be used as the basis for a soil policy framework with soil carbon as an exemplar indicator.

Rare earth element trends and cerium-uranium-manganese associations in weathered rock from Koongarra, Northern Territory, Australia

At Koongarra, Australia, three drill cores form the Cahill Schist Formation containing U-ore, and regolith above it containing secondary U-ore, were studied to ascertain the distribution of rare earth elements (REEs) and U. The unaltered schist has a REE trend similar to the Post Archaean Australian Shale (PAAS), which is, therefore, used as a normalising standard. Unweathered rock from the zone of primary U mineralisation contained strong enrichment of the heavy REEs, and this pattern is retained during most of the weathering. Strongly bleached and very weathered shallow samples from this zone do not show enrichment of HREEs. In general, however, weathering appears to have little effect on the pattern of REEs in the bulk rock at this site. Zones rich in Mn oxy-hydroxides, occurring as coatings on fissure surfaces, contain large concentrations of Ce and U, with a clear Ce anomaly (Ce/Ce* = 3.8). The Ce and U apparently occur together as microcrystalline oxides within (1-2 {mu}m diameter) globules on mineral surfaces in the Mn-rich zones. 46 refs., 10 figs., 2 tabs.

A description of aggregate liberation and dispersion in A horizons of Australian Vertisols by ultrasonic agitation

A theory is proposed which is analogous to a first-order consecutive reaction to describe the stepwise breakdown of an aggregate hierarchy for Vertisols subjected to ultrasonic agitation. To explain the liberation and subsequent dispersion of microaggregates as increasing ultrasonic energy is applied the aggregate liberation and dispersion curve (ALDC) is developed. It is found that the prominence and shape of the curve is dependent on the rate constants, which explain the rate of microaggregate liberation and subsequent dispersion. From this curve it is possible to estimate the maximum mass of microaggregates, which is not only dependant on the rate constants, but also the availability of clay that form the microaggregates. The resulting ALDC for the sample also enables the estimation of the total energy applied needed to initiate dispersion of the liberated microaggregates. It is found that the relative stability of the micoraggregates are correlated with some of the chemical properties (ESP and CaCO3) of the samples.

Modelling aggregate liberation and dispersion of three soil types exposed to ultrasonic agitation

This paper reports on a study involving the application of ultrasonic agitation to 3 soil types to assess soil aggregate disruption and subsequent dispersion. The measurement of various particle size fractions resulting after the application of ultrasonic agitation for different time periods made it possible to describe the resulting aggregate disruption using the established aggregate liberation and dispersion curve (ALDC) model. Originally this model had been used to assess only the 2-20 µm fraction liberated from Vertosols. This work has shown that the model can be applied to a variety of size fractions between 2 and 100 µm in diameter and soil types, namely Chromosols and Ferrosols. By estimating the critical energy (Ecrit) required to initiate dispersion of liberated aggregates for each fraction, it is implied that the linkage between aggregates is weaker than the linkages between the materials composing the aggregates. Further, the ratio between the rate constants in the ALDC model can be used to establish if there is a stepwise breakdown of larger aggregates, a criterion required to establish the presence of an aggregate hierarchy. Finally, by assessing the aggregate distribution on a continuous scale, it is possible to recognise unique pathways of aggregate liberation and dispersion for each soil type rather than assuming that aggregates breakdown into predefined discrete size fractions. Additional keywords: soil aggregates, ultrasonic methods, soil mechanical properties, soil dynamics, aggregate distribution.

Challenges for Soil Organic Carbon Research

The soil body is the largest terrestrial pool of organic carbon globally. Lately, research related to soil organic carbon has been a main focus worldwide, motivated by the potential the soil inhabits to become a manageable sink for atmospheric carbon dioxide and thus to mitigate climate change and the known benefits of increased soil organic carbon for the functioning of soils. Here, challenges are highlighted for soil organic carbon research that we are currently facing. Knowledge on soil organic carbon dynamics in the soil system is briefly reviewed, followed by an elaboration on how soil organic carbon dynamics and soil organic carbon stocks have been modelled in space and time and where modelling needs to go.

Securing our soil

Abstract Through the recognition and interplay of biochemicophysical (pedologic and edaphic), economic, social and policy dimensions, soil security is a wider and more integrative concept than previous policy- and management-focused notions such as soil conservation, soil care, soil quality, soil health and soil protection. It is the soil homolog of food, water and energy security. In this way, global significance of soil for sustainable development is emphasized. Through the five dimensions of soil security, the value of soil in addressing at least six of the current global existential challenges is formulated, and the intrinsic import of soil security as an equally essential worldwide pragmatic requirement is resolved. The immediate quest is for a multidisciplinary understanding to qualify and quantify the five dimensions effectively and efficiently so that the security of soil in fields, catchments or watersheds, regions, countries, continents and globally can be measured, maintained or improved through appropriate management and policy, and monitored on an ongoing basis.

Comparison of four methods for liberating various aggregate fractions in Vertosols to study their morphology

Topsoil samples from 3 Vertosols located at Narrabri, Warren, and Dalby were treated with 4 aggregate liberation methods to determine their suitability for analysis by scanning electron microscopy (SEM). In addition to the ability of each method to liberate aggregates for assessment, the potential for consequent morphological deformation was also considered. It was found that the aggregate slaking in water and modified wet sieving methods were suitable for liberating aggregates >100 μm in diameter, whereas the ultrasonic agitation method readily liberated aggregates 250, 100–250, 20–100, 2–20, and <2 μm in diameter.

Relationships between field texture and particle-size distribution in Australia and their implications

This paper aims to establish the means and ranges of clay, silt, and sand contents from field texture classes, and to investigate the differences in the field texture classes and texture determined from particle-size analysis. The results of this paper have 2 practical applications: (1) to estimate the particle size distribution and its uncertainty from field texture as input to pedotransfer functions, and (2) to examine the criteria of texture contrast soils in the Australian Soil Classification system. Estimates of clay, silt, and sand content for each field texture class are given and this allows the field texture classes to be plotted in the texture triangle. There are considerable differences between field texture classes and particle-size classes. Based on the uncertainties in determining the clay content from field texture, we establish the probability of the occurrence of a texture contrast soil according to the Australian Soil Classification system, given the texture of the B2 horizon and its overlying A horizon.

Synthesis: Goals to Achieve Soil Security

To work towards achieving soil security in the next two decades, participants identified goals to secure soil so that it can contribute to solving other global issues. Specific goals for each dimension were designed to achieve the overall objective of soil security, catalyse research and practice and contribute to soil policy.

Soil Security: A Rationale

The concept of soil security has strategic value in that it can serve to focus and guide the development of policies addressing the six global existential challenges, such that interventions for one challenge result in favourable effects on other challenges. Soil security arises from both top-down (global challenge) and bottom-up (societal value) considerations. We envision it as a homologous concept to those of food and water security. The major goal is to measure and manage the five dimensions of capability, condition, capital, connectivity and codification.