Daniel Lee Evans

Soil is the foundation of life itself, and without healthy soils our day‐to‐day lives would be forever changed. A significant proportion of soil science focuses on the topsoil, overlooking much of the soil profile. If soil science is to fully serve society, we must expand our understanding to the full soil–bedrock continuum, extending beyond the top 30 cm into the deeper profile that includes weathered bedrock. This argument has been raised before, with many scientists calling for whole‐profile sampling and characterization, yet these calls have gone largely unheeded, and recent studies suggest we may even be narrowing our focus to shallower depths. In this opinion, we present the case for studying the full soil profile by examining its historical treatment, current paradigms, and we highlight some of the opportunities that are being missed. To fully understand and steward the systems that underpin life: we must be willing to go deeper in our sampling, in our thinking, and in our collaborations across disciplines.

Background and aims: Certain plant species, including some trees, have been observed growing not only in soil but also in soil parent materials. However, the root traits and mechanisms enabling these species to penetrate soil parent materials are not yet thoroughly understood. This systematic review aims to identify and discuss the root traits and mechanisms that allow plant roots to grow into soil parent materials. It will also draw insights from the characteristics and mechanisms that plants employ to overcome the challenges posed by compacted soils. Methods: We adhered to the 'Preferred Reporting Items for Systematic Reviews and Meta-Analyses' (PRISMA) guidelines for our methodology. Results: We identified increased root radial pressure, investment in root biomass, fine root development, root trematotropism, mycorrhizal associations, root hairs, and root exudates as key traits aiding plants in soil penetration. The mentioned root traits and mechanisms have also been shown to help plants overcome compacted soil, except for mycorrhizal associations. Conclusion: The key root traits and mechanisms identified in this review lay the groundwork for a deeper understanding of root-soil parent material interactions and plant adaptations in changing physical environments. This enhances our ability to select the next generation of robust and resilient crops capable of thriving in complex root-soil parent material interactions. Future research on root-parent material interactions in food crops holds promise for improving our understanding of how crops can grow beyond traditional soil limitations (such as soil depth).

Intensifying effects of global climate change have spurred efforts to enhance carbon sequestration and the long‐term storage of soil organic carbon (OC). Current soil carbon models predominantly assume that inputs of OC are biospheric, that is, primarily derived from plant decomposition. However, these overlook the contribution of OC from soil parent material, including petrogenic organic carbon (OC_petro) from OC‐bearing (meta‐)sedimentary bedrock. To our knowledge, no soil carbon model accounts for the inputs of OC_petro to soils, resulting in significant gaps in our understanding about the roles OC_petro plays in soils. Here, we call for cross‐disciplinary research to investigate the transport and stability of OC_petro across the bedrock–soil continuum. We pose four key questions as motivation for this effort. Ignoring the inputs of OC_petro to soils has significant implications, including overestimating biospheric carbon stocks and turnover times. Furthermore, we lack information on the role that OC_petro may play in priming microbial communities, as well as the impacts of land management on OC_petro stocks.

Over the past decade, both national (UK) and multilateral (EU) climate legislation have significantly accelerated research efforts to mitigate soil carbon emissions, enhance soil organic carbon (OC) sequestration, and promote long-term OC storage. However, these efforts face substantial challenges. Increasing demands on land use and the resulting land-cover changes often lead to significant net losses of OC. Furthermore, climate warming exacerbates OC losses through accelerated decomposition processes. Although the soil carbon reservoir has a finite capacity, its potential is limited by an arbitrary boundary: the lower limit of soil profiles, separating them from the underlying zone of soil parent material. Soil parent materials consist of consolidated substrates (e.g., weathered rock) and unconsolidated ones (e.g., alluvium) from which soils primarily develop. Emerging evidence indicates that soil parent materials has stores of biogenic organic carbon. However, our understanding of the stability of carbon at the interface between soil parent materials and soils remains limited. This presentation explores the stability of organic carbon within soil parent materials, focusing specifically on the effects of priming on OC stability.

Soil moisture plays a vital role in agriculture, drought management, and flood prevention. It is essential for plant growth and sustainable farming practices. In flood-prone areas, soil's ability to retain water helps absorb excess moisture and reduce runoff, mitigating flood risks. Therefore, effective soil moisture monitoring is crucial for informed irrigation and water management decisions. Various methods exist for measuring soil moisture, both in-situ and remote. In-situ techniques, like volumetric and gravimetric sampling, provide real-time data but are limited to specific locations unless interpolation is applied. On the other hand, remote sensing offers broader spatial coverage but often with lower resolution and accuracy. While remote sensing can validate ground-based data, it is less effective for capturing short-term changes, such as those resulting from irrigation, at fine temporal scales.To address these challenges, we are developing UAV-RADAR, the first multiband Synthetic Aperture Radar (SAR) mounted on a drone. Unlike conventional SAR platforms (e.g., Sentinel-1), UAV-RADAR provides rapid, high-resolution, and scalable soil moisture data tailored to specific agricultural and environmental contexts. Its customizable flight plans enable detailed pre- and post-treatment analyses, capturing temporal changes with unprecedented flexibility.In this presentation, we will showcase our current research and development of UAV-RADAR to date, demonstrating its capability to measure soil moisture across diverse soil types, landscapes, and agricultural practices. Using data from proof-of-concept experiments carried out in England and Wales, we will show soil moisture maps and demonstrate their applications. We will highlight use cases, and explore how UAV-RADAR can contribute to initiatives like the International Soil Moisture Network.

Soil organic carbon is essential for sustaining soil health and functioning and for achieving the United Nations Sustainable Development Goals. However, soil carbon research to date has focused predominantly on the surface horizons of soil, with fewer studies accounting for the carbon stored down the whole soil profile. Rarer still are assessments of the organic carbon (OC) stored in soil parent materials, in spite of their pervasive presence beneath almost all soil profiles. As a result, our understanding about the storage, functioning, and long‐term stability of OC within soil parent materials is sparse. This exacerbates the challenge of maximizing soil carbon sequestration and achieving Net Zero Carbon targets that require, in the first instance, a holistic account of all carbon pools and sequestration processes, including those that take place across the transition between soils and their parent materials. This study aims to establish the foundation of an evidence base by comparing the stocks of OC measured down agricultural soil profiles with the stocks in their associated parent materials. Sampling of soil and saprolite (i.e., weathered rock) was conducted across three lithologies in the United Kingdom, and thermogravimetric analysis was used to determine both the total OC content and its relative stability (i.e., labile or recalcitrant fractions). OC stocks within saprolite were statistically similar to those measured in overlying soil profiles. This was especially the case for shallow soils where the saprolite is within the effective rooting depth of crops. The ratios of labile to recalcitrant carbon indicated that the OC within saprolite was predominantly persistent but labile when saprolite was close to the land surface. These findings underscore the importance of including soil parent materials in soil carbon studies and opens up new opportunities to design strategies that enhance soil carbon sequestration within the soil parent material zone.

Terrestrial environments and their ecosystems demand healthy, sustainable, and resilient soils. Over the past couple of decades, significant efforts have been made to safeguard global soils, yet the materials and resources responsible for soil formation have been widely overlooked. The transition from bedrock to soil – a zone often described as ‘soil parent material’ – holds an exciting yet untapped potential for helping us address some of the largest environmental challenges, including climate change and the biodiversity crisis. In this award lecture, I will present a strand of my research programme ‘Building Tomorrow’s Soils’ which seeks to establish how soil parent materials enhance the sustainability, health, and resilience of soil systems. First, with a focus on carbon sequestration, I will highlight how the bedrock–soil transition zone has the potential to be a long-term store of organic carbon. I will then present research which shows that some soil parent materials release petrogenic (i.e. rock-derived) organic carbon into soils. These understudied inputs of organic carbon to soils are currently absent from most, if not all, soil carbon models, which threatens our ability to optimize soil carbon management in the long-term. Finally, I will argue that developing a mechanistic understanding about this transition zone – this underexplored material which is neither rock nor soil in structure and function, but a blend of both – requires a similarly cross-disciplinary approach.

Soil parent material is a fundamental natural resource for the generation of new soils. Through weathering processes, soil parent materials provide many of the basic building blocks for soils and have a significant bearing on the physico-chemical makeup of the soil profile. Parent materials are critical for governing the stock, quality, and functionality of the soil they form. Most research on soil parent materials to date has aimed to establish and measure the processes by which soil is generated from them. Comparatively little work has been performed to assess the rates at which soil parent materials erode if they are exposed at the land surface. This is despite the threat that the erosion of soil parent materials poses to the process of soil formation and the loss of the essential ecosystem services those soils would have provided. A salient but unanswered question is whether the erosion of soil parent materials, when exposed at the land surface, outpaces the rates at which soils form from them. This study represents one of the first to detect and measure the loss of soil parent material. We applied Uncrewed Aerial Vehicle Structure-From-Motion (UAV-SfM) photogrammetry to detect, map, and quantify the erosion rates of an exposed saprolitic (i.e., weathered bedrock) surface on an agricultural hillslope in Brazil. We then utilized a global inventory of soil formation to compare these erosion rates with the rates at which soils form in equivalent lithologies and climatic contexts. We found that the measured saprolite erosion rates were between 14 and 3766 times faster than those of soil formation in similar climatic and lithological conditions. While these findings demonstrate that saprolite erosion can inhibit soil formation, our observations of above-ground vegetation on the exposed saprolitic surface suggests that weathered bedrock has the potential to sustain some biomass production even in the absence of traditional soils. This opens up a new avenue of enquiry within soil science: to what extent can saprolite and, by extension, soil parent materials deliver soil ecosystem services?