Soil properties drive microbial community structure in a large scale transect in South Eastern Australia

Soil microbial communities directly affect soil functionality through their roles in the cycling of soil nutrients and carbon storage. Microbial communities vary substantially in space and time, between soil types and under different land management. The mechanisms that control the spatial distributions of soil microbes are largely unknown as we have not been able to adequately upscale a detailed analysis of the microbiome in a few grams of soil to that of a catchment, region or continent. Here we reveal that soil microbes along a 1000 km transect have unique spatial structures that are governed mainly by soil properties. The soil microbial community assessed using Phospholipid Fatty Acids showed a strong gradient along the latitude gradient across New South Wales, Australia. We found that soil properties contributed the most to the microbial distribution, while other environmental factors (e.g., temperature, elevation) showed lesser impact. Agricultural activities reduced the variation of the microbial communities, however, its influence was local and much less than the overall influence of soil properties. The ability to predict the soil and environmental factors that control microbial distribution will allow us to predict how future soil and environmental change will affect the spatial distribution of microbes

Microbial decomposition of organic matter and wetting–drying promotes aggregation in artificial soil but porosity increases only in wet-dry condition

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 matter and wetting and drying of soil promotes aggregation and changes in pore geometry. Using microcosms of silicate clays and sand with either rapidly decomposable glucose or slowly decomposable cellulose, the degree of aggregation (P < 0.001), was greater in glucose treatments than controls that did not receive added carbon or microbial inoculum. We link this to microbial activity through measurements in soil respiration, phospholipids and microbially derived carbon. Our results demonstrate that rapid microbial decomposition of organic matter and microbially derived carbon promote aggregation and the aggregation process was particularly strong in the wet-dry condition (alternating between 30 % and 15 % water content) with significant modification of porosity (P < 0.05) of the aggregates

Estimation and Potential Improvement of the Quality of Legacy Soil Samples for Digital Soil Mapping

Legacy soil data form an important resource for digital soil mapping and are essential for calibration of models for predicting soil properties from environmental variables. Such data arise from traditional soil survey. Methods of soil survey are generally empirical and based on the mental development of the surveyor, correlating soil with underlying geology, landforms, vegetation and air-photo interpretation. There are no statistical criteria for traditional soil sampling, and this may lead to biases in the areas being sampled. The challenge is to use legacy data for large-area mapping (e.g. national or continental) as funds are limited to resample large areas. The problem is then to assess the reliability and quality of the legacy soil databases that have been mainly populated by traditional soil survey, and if there is a possibility of additional funding for sampling, where should new sampling units be located. This additional sampling can be used to improve and validate the prediction model. Latin hypercube sampling (LHS) has been proposed as a sampling design for digital soil mapping when there is no prior sample. We use the principle of hypercube sampling to assess the quality of existing soil data and guide us to the area that needs to be sampled. First an area is defined and the empirical environmental data layers or covariates are identified on a regular grid. The existing soil data is matched with the environmental variables. The HELS spell out algorithm is used to check the occupancy of the legacy sampling units in the hypercube of the quantiles of the covarying environmental data1 . This is to determine whether legacy soil survey data occupy the hypercube uniformly or if there is over- or under-observation in the partitions of the hypercube. It also allows posterior estimation of the apparent probability of sample units being surveyed. From this information we can design further sampling. The methods are illustrated using legacy soil samples from Edgeroi, New South Wales, Australia, and from a large part of the Danube Basin.JRC.H.7-Land management and natural hazard

A global numerical classification of the soil surface layer

International audienc

Participatory approaches for soil research and management: A literature-based synthesis

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 is diverse and applied variously, ranging from data collection to inform large-scale monitoring schemes in citizen science projects to projects in which the participants define the object of study and the questions to be answered. The growth of participatory projects to tackle complex environmental and soil-related issues has generated literature that describes both the way the projects are initiated, implemented and the outcomes they achieve. We review the existing literature on participatory soil research and management. Existing studies are classified into three categories based on the degree of participation in the different phases of research. The quality of participation is further evaluated systematically through the five elements that participatory projects usually include: inputs, activities, outputs, outcomes and impacts. We found that the majority of existing participatory projects were contributory in nature, where participants contribute to generating data. Co-created projects which involve a greater level of participation are less frequent. We also found large disparities in the context in which these types of participation occurred: contributory projects were mostly documented in more economically developed countries, whereas projects that suggest greater involvement of participants were mostly formulated in developing countries in relation to soil management and conservation issues. The long-term sustained outcomes of participatory projects on human well-being and socio-ecological systems are seldom reported. We conclude that participatory approaches are opportunities for education, communication and scientific progress and that participation is being facilitated by digital convergence. Participatory projects should, however, also be evaluated in terms of their long-term impact on the participants, to be sure that the expectations of the various parties align with the outcomes. All in all, such participation adds to the quantum of soil connectivity and in this sense makes the soil more secure globally

A global numerical classification of the soil surface layer

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, there remain various examples of their shortcoming in accounting of topsoil features, local applications and communication with established regional classification systems. This calls for a numerical soil classification that addresses these discrepancies and achieves harmonization with existing national systems. In this paper, we report on the development of a natural layer classification system — as opposed to the classification of soil profile entities, as a first step towards achieving a comprehensive global numerical soil classification not based on a priori defined classes. We implemented a modelling approach with a set of predicted key soil properties available globally for the soil surface layer with the same depth range of 0–5 cm. The set of properties was partitioned into a number of homogeneous and disjoint classes using the k-means clustering algorithm. Next, we investigated the pattern of variation of the clusters in association with the soil property map with principal component analysis. A three-component nomenclature system is derived in a transformed space of the class-specific centroids to account for the uneven distribution of the centroids in the principal component space. We show that it is possible to build a data-based objective numerical taxonomic classification of soil layers, and that existing sets of key soil properties, predicted separately, coalesce into identifiable clusters or classes and manifest discernible spatial and/or pedological patterns. This grouping of key soil properties to logical categories is a possible step to better define diagnostic horizon features and suggest new ones. The general-purpose map of soil surface layer classes of the world also has potential applications in assessing soil change and designing monitoring surveys

Description and spatial inference of soil drainage using matrix soil colours in the Lower Hunter Valley, New South Wales, Australia

Soil colour is often used as a general purpose indicator of internal soil drainage. In this study we developed a necessarily simple model of soil drainage which combines the tacit knowledge of the soil surveyor with observed matrix soil colour descriptions. From built up knowledge of the soils in our Lower Hunter Valley, New South Wales study area, the sequence of well-draining → imperfectly draining → poorly draining soils generally follows the colour sequence of red → brown → yellow → grey → black soil matrix colours. For each soil profile, soil drainage is estimated somewhere on a continuous index of between 5 (very well drained) and 1 (very poorly drained) based on the proximity or similarity to reference soil colours of the soil drainage colour sequence. The estimation of drainage index at each profile incorporates the whole-profile descriptions of soil colour where necessary, and is weighted such that observation of soil colour at depth and/or dominantly observed horizons are given more preference than observations near the soil surface. The soil drainage index, by definition disregards surficial soil horizons and consolidated and semi-consolidated parent materials. With the view to understanding the spatial distribution of soil drainage we digitally mapped the index across our study area. Spatial inference of the drainage index was made using Cubist regression tree model combined with residual kriging. Environmental covariates for deterministic inference were principally terrain variables derived from a digital elevation model. Pearson’s correlation coefficients indicated the variables most strongly correlated with soil drainage were topographic wetness index (−0.34), mid-slope position (−0.29), multi-resolution valley bottom flatness index (−0.29) and vertical distance to channel network (VDCN) (0.26). From the regression tree modelling, two linear models of soil drainage were derived. The partitioning of models was based upon threshold criteria of VDCN. Validation of the regression kriging model using a withheld dataset resulted in a root mean square error of 0.90 soil drainage index units. Concordance between observations and predictions was 0.49. Given the scale of mapping, and inherent subjectivity of soil colour description, these results are acceptable. Furthermore, the spatial distribution of soil drainage predicted in our study area is attuned with our mental model developed over successive field surveys. Our approach, while exclusively calibrated for the conditions observed in our study area, can be generalised once the unique soil colour and soil drainage relationship is expertly defined for an area or region in question. With such rules established, the quantitative components of the method would remain unchanged

Simulation of soil thickness evolution in a complex agricultural landscape at fine spatial and temporal scales

Hedgerow networks in the landscape are adapted objects that can be used to study soil redistribution processes within the landscape. In hedged landscapes, water erosion redistributes soil, but hedges act as barriers to the physical transfers of soil particles. The most systematic effect is the increase in the thickness of A-horizons uphill from the hedges. A field experiment was carried out within an old agricultural area with a high density of hedges. A high resolution digital elevation model and a soil thickness map were created to investigate the effect of hedges on soil reorganization. The aims of this paper are to use this pedological knowledge for a better understanding of process dynamics, to simulate quantitatively the effect of hedgerow network on soil organization and redistribution, and to test different scenarios of land management on soil redistribution dynamics. The simulation uses a mechanistic model where the change in soil thickness over time depends on the transport of soil through a diffusive transport and a water erosion process. We tested the suitability of the model to operate on a DEM with grid size of 1 m and a simulation time of less than 1200 years. We performed the simulations on theoretical and actual DEMs with and without the hedgerow network. The effect of different land use and management scenarios on soil redistribution was tested. Those scenarios were applied on a DEM of real landscape, with the addition and removal of hedge on the DEM. The results suggest that the combination of diffusive transport and water erosion could significantly modify the topography and soil redistribution over a few centuries. The simulations show that hedges modify soil distribution and landforms by favouring deposition in the uphill position and soil erosion in the downhill position in agreement with field observations