Environment and Rural Affairs Monitoring & Modelling Programme ERAMMP report-70: The use of remote sensing to assess soil erosion, poaching and disturbance features

Soil is a finite resource. Within the concepts of natural capital and ecosystem services, the erosion and compaction of soil are considered to be major threats to both ‘soil stock’ and ‘soil function’. Principal drivers of erosion include slope angle and length, precipitation quantity and intensity and vegetation coverage. Soil compaction (primarily caused by repeated movements by vehicles or poaching by animals leading to exposed soils) may reduce soil function in terms of water and gaseous movement and exacerbate N2O emission, as well as potentially creating pathways for erosion to occur. However, producing national scale assessments of soil erosion is expensive and difficult, whilst soil compaction, or disturbance remains largely unconsidered in assessments. Soil erosion is a compliance issue, however, the work outlined in this report is not aligned with any regulatory or compliance process such as outlined in Good Agriculture and Environmental Conditions 5 (Welsh Govt, 2022); it is purely a research project for the monitoring and assessment of soils. Many methods for measuring soil erosion exist and are used over a range of different spatial scales. These include plot experiments, field or catchment studies. However, widespread quantification of erosion rates are time consuming and still remain spatially restricted. Other approaches are more suited to national scale assessments. Modelling approaches, usually based on the ‘Universal Soil Loss Equation’ or its variants can provide an indication as to where long-term erosion is most likely to occur under certain land-use and climatic conditions and are useful for looking at potential change. Walk-over-surveys have the potential to measure area and sometimes volumes of soil erosion, but are also time consuming to undertake. However, they do provide the most repeatable basis for widespread or national scale monitoring. The use of earth observation presented here, combined with field survey, may be an effective and less time-consuming approach for the assessment of national scale soil erosion, but its benefits and limitations need to be explored. This study reports on (i) a desk-based soil erosion and disturbance survey undertaken using high resolution aerial images (0.25 m); and (ii) a subsequent ground survey of the aerial photo survey undertaken as part of the 2021 ERAMMP field survey

Multiple soil map comparison highlights challenges for predicting topsoil organic carbon concentration at national scale

Soil organic carbon (SOC) concentration is the fundamental indicator of soil health, underpinning food production and climate change mitigation. SOC storage is highly sensitive to several dynamic environmental drivers, with approximately one third of soils degraded and losing carbon worldwide. Digital soil mapping illuminates where hotspots of SOC storage occur and where losses to the atmosphere are most likely. Yet, attempts to map SOC often disagree. Here we compare national scale SOC concentration map products to reveal agreement of data in mineral soils, with progressively poorer agreement in organo-mineral and organic soils. Divergences in map predictions from each other and survey data widen in the high SOC content land types we stratified. Given the disparities are highest in carbon rich soils, efforts are required to reduce these uncertainties to increase confidence in mapping SOC storage and predicting where change may be important at national to global scales. Our map comparison results could be used to identify SOC risk where concentrations are high and should be conserved, and where uncertainty is high and further monitoring should be targeted. Reducing inter-map uncertainty will rely on addressing statistical limitations and including covariates that capture convergence of physical factors that produce high SOC contents

Quantifying the impact of microbes on soil structural development and behaviour in wet soils

There is evidence that microbial populations play an important role in altering soil pore geometry, but a full understanding of how this affects subsequent soil behaviour and function is still unclear. In particular the role of microorganisms in soil structural evolution and its consequence for pore morphological development is lacking. Using a combination of bio-chemical measurements and X-ray Computed Tomography (CT) imaging, a temporal comparison of microscale soil structural development in contrasting soil environments was made. The aim was to quantify the effect of microbial activity in the absence of other features likely to cause soil deformation (e.g. earthworms, roots etc.) on soil structural development in wet soils, defined by changes in the soil porous architecture i.e. pore connectivity, pore shape and pore volume during a 24 week period. Three contrasting soil textures were examined and changes compared between field soil, sterilised soil and a glucose enhanced soil treatment. Our results indicate that soil biota can significantly alter their microhabitat by changing soil pore geometry and connectivity, primarily through localised gaseous release. This demonstrates the ability of microorganisms to modify soil structure, and may help reveal the scope by which the microbial-rich rhizosphere can locally influence water and nutrient delivery to plant roots

Do development and learning really decrease memory? On similarity and category-based induction in adults and children

In a recently published study, Sloutsky and Fisher [Sloutsky, V. M., & Fisher, A.V. (2004a). When development and learning decrease memory: Evidence against category-based induction in children. Psychological Science, 15, 553–558; Sloutsky, V. M., & Fisher, A. V. (2004b). Induction and categorization in young children: A similarity-based model. Journal of Experimental Psychology: General, 133, 166–188.] demonstrated that children have better memory for the items that they generalise to than do adults. On the basis of this finding, they claim that children and adults use different mechanisms for inductive generalisations; whereas adults focus on shared category membership, children project properties on the basis of perceptual similarity. Sloutsky & Fisher attribute children’s enhanced recognition memory to the more detailed processing required by this similarity-based mechanism. In Experiment 1 we show that children look at the stimulus items for longer than adults. In Experiment 2 we demonstrate that although when given just 250 ms to inspect the items children remain capable of making accurate inferences, their subsequent memory for those items decreases significantly. These findings suggest that there are no necessary conclusions to be drawn from Sloutsky & Fisher’s results about developmental differences in generalisation strategy

Analytical modelling of soil porosity and bulk density across the soil organic matter and land-use continuum

The thin layer of soil at the earth’s surface supports life, storing water and nutrients for plant uptake. These processes occur in the soil pore space, often half the soil volume, but our understanding of how this volume responds to environmental change is poor. Convention, has been to predict soil porosity, or its reciprocal bulk density (BD), from soil texture using pedotransfer functions (PTFs). A texture based approach, invariant to environmental change, prevents feedback from land use or climate change to soil porosity. Moreover, PTFs are often limited to mineral soils with < 20% soil organic matter (SOM) content. Here, we develop an analytical model to predict soil porosity, or BD, as a function of SOM. We test it on two comprehensive, methodologically consistent, temperate national-scale topsoil data sets (0–15 cm) (Wales, n = 1385; Great Britain, n = 2570). The purpose of the approach is to generate an analytical function suitable for predicting soil porosity change with SOM content, while providing insight into the main grain-scale factors determining the porosity emergence. The newly developed function covering the entire SOM gradient allows for impacts of land use, management or climate change to feedback on soil porosity or bulk density through decadal dynamic changes in SOM