Efficient sampling for geostatistical surveys

A geostatistical survey for soil requires rational choices regarding the sampling strategy. If the variogram of the property of interest is known then it is possible to optimize the sampling scheme such that an objective function related to the survey error is minimized. However, the variogram is rarely known prior to sampling. Instead it must be approximated by using either a variogram estimated from a reconnaissance survey or a variogram estimated for the same soil property in similar conditions. For this reason, spatial coverage schemes are often preferred, because they rely on the simple dispersion of sampling units as uniformly as possible, and are similar to those produced by minimizing the kriging variance. If extra sampling locations are added close to those in a spatial coverage scheme then the scheme might be broadly similar to one produced by minimizing the total error (i.e. kriging variance plus the prediction error due to uncertainty in the covariance parameters). We consider the relative merits of these different sampling approaches by comparing their mean total error for different specified random functions. Our results showed the considerable benefit of adding close‐pairs to a spatial coverage scheme, and that optimizing with respect to the total error generally gave a small further advantage. When we consider the example of sampling for geostatistical survey of clay content of the soil, an optimized scheme based on the average of previously reported clay variograms was fairly robust compared to the spatial coverage plus close‐pairs scheme. We conclude that the direct optimization of spatial surveys was only rarely worthwhile. For most cases, it is best to apply a spatial coverage scheme with a proportion of additional sampling locations to provide some closely spaced pairs. Furthermore, our results indicated that the number of observations required for an effective geostatistical survey depend on the variogram parameters

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

Challenge 7 : How to recognize, quantify and map soil functionality?

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Spatial evaluation of the soils capacity and condition to store carbon across Australia

International audienceThe 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 the framework for the function soil carbon storage and the two dimensions of soil capacity and soil condition. The methodology consists of (i) the selection and quantification of a small set of soil indicators for capacity and condition, (ii) the transformation of indicator values to unitless utility values via expert-generated utility graphs, and (iii) a two-level aggregation of the utility values by soil profile and by dimension. For capacity, we used a set of three indicators: total organic and inorganic carbon content and mineral associated organic carbon in the fine fraction (MAOC) estimated via their reference value using existing maps of pedogenons and current landuse to identify areas of remnant genosoils (total organic and inorganic carbon) and the 90th percentile for MAOC. For condition we used the same set of indicators, but this time using the estimated current value and comparing with their reference-state values (calculated for capacity). The methodology was applied to the whole of Australia at a spatial resolution of 90 m x 90 m. The results show that the unitless indicator values supporting the function varied greatly in Australia. Aggregation of the indicators into the two dimensions of capacity and condition revealed that most of Australia has a relatively low capacity to support the function, but that most soils are in a generally good condition relative to that capacity, with some exceptions in agricultural areas, although more sampling of the remnant genosoils is required for corroboration and improvement. The maps of capacity and condition may serve as a basis to estimate a spatially-explicit local index of Australia’s soil resilience to the threat of decarbonization

A proposal for the assessment of soil security: Soil functions, soil services and threats to soil

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-economic dimensions of capacity, condition, capital, connectivity and codification. In this paper, we highlight past and existing concepts, and make a proposal for a provisional assessment of soil security. The proposal addresses three roles of soil: soil functions, soil services and threats to soil. For each identified role, we indicate a potential, but not exhaustive, list of indicators that characterise the five dimensions of soil security. We also raise issues of quantification and combination of indicators briefly. We found that capacity and condition are theoretically easier to measure and quantify than connectivity and codification. The dimension capital might be conveniently assessed using indicators that relate to the economic value of soils. The next step is to test this proposal for which we make recommendations on potential study cases and examples. We conclude that the five dimensions of soil security can potentially be assessed quantitatively and comprehensively using indicators that characterise each role, but also found that there is need for further work to devise an operational measurement methodology to estimate connectivity of people to soil

The Theia “Digital Soil Mapping” Scientific Expertise Centre of France

International audiencepas de résum

Un projet de formation francophone en télédétection et cartographie des sols par modélisation statistique

International audienc

Un projet de formation francophone en télédétection et cartographie des sols par modélisation statistique

International audienc

The Theia "Digital Soil Mapping" Scientific Expertise Centre of France

International audienc