P. D. Hallett

P. D. Hallett
University of Aberdeen | ABDN · Institute of Biological and Environmental Sciences

BSc Agriculture (Guelph), PhD (Birmingham)

About

214
Publications
83,214
Reads
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Citations
Introduction
Confused soil scientist who switches between being a physicist and a biologist, but usually ends up doing both at the same time. Most of my current work investigates root:soil structure interactions, ranging in scale from the rhizosphere to in-field impacts of soil management.
Additional affiliations
September 2014 - present
University of Aberdeen
Position
  • MSc Soil Science - Course Coordinator
Description
  • This is the last MSc in Soil Science in the UK. Come to Aberdeen if you would like a dedicated course taught by a range of soil scientists with different specialisations.
April 2013 - present
University of Aberdeen
Position
  • Professor of Soil Physics
Description
  • I use approaches from soil physics, materials science and engineering to quantify mechanical and hydrological processes that underlie the physical engineering of soil by biology. This knowledge is applied to food and environmental security challenges.
April 2011 - April 2013
The James Hutton Institute, Dundee, United Kingdom
Position
  • Theme Leader - Delivering Sustainable Production Systems
Description
  • The research Theme brought together a broad range of disciplines to investigate more sustainable agriculture system. I also carried out an independent research programme on soil biophysics.

Publications

Publications (214)
Article
Full-text available
Aims Recent laboratory studies revealed that root hairs may alter soil physical behaviour, influencing soil porosity and water retention on the small scale. However, the results are not consistent, and it is not known if structural changes at the small-scale have impacts at larger scales. Therefore, we evaluated the potential effects of root hairs...
Article
Background and Aims: Previous laboratory studies have suggested selection for root hair traits in future crop breeding to improve resource use efficiency and stress tolerance. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. As such, this study aims to experimenta...
Article
Full-text available
Aims Reduced tillage has been advocated as a practical measure to increase soil carbon in long-term cropping soils. We examine three medium-term experiments in sites with contrasting soil and climatic characteristics in the UK. The objectives were to determine the effects of different reduced and zero tillage practices on bulk density and soil carb...
Article
Background and aims: Previous laboratory studies have suggested selection for root hair traits in future crop breeding to improve resource use efficiency and stress tolerance. However, data on the interplay between root hairs and open-field systems, under contrasting soils and climate conditions, are limited. As such, this study aims to experiment...
Article
Tropical soils tend to harden during drying due to the generally low content of free-iron and organic carbon, combined with high fine sand and silt proportions. It was hypothesized that the change in soil physical condition induced by the addition of a leguminous mulch in cohesive tropical soil enriched with calcium may mitigate soil hardening thro...
Article
Full-text available
Leaching of nitrate from fertilisers diminishes nitrogen use efficiency (the portion of nitrogen used by a plant) and is a major source of agricultural pollution. To improve nitrogen capture, grasses such as brachiaria are increasingly used, especially in South America and Africa, as a cover crop, either via intercropping or in rotation. However, t...
Article
Biological exudates, such as plant mucilage, can greatly stabilize soils, but as the mechanical and hydrological drivers depend much on soil particle size composition, eroding and depositional areas of a slope may respond differently. Soils from an eroded midslope and a depositional footslope in an arable farm were amended with chia (Salvia hispani...
Article
Full-text available
Background and aims: root hairs play a significant role in phosphorus (P) extraction at the pore scale. However, their importance at the field scale remains poorly understood. Methods: this study uses a continuum model to explore the impact of root hairs on the large scale uptake of P, comparing root hair influence under different agricultural sce...
Article
Full-text available
Recent discoveries of polyhalite (K2SO4.MgSO4.2CaSO4.2H2O) in the UK provide an alternative to conventional fertilizer sources. This work investigated the interaction of polyhalite, commercially known as POLY4, with soil using leaching columns. Different physical forms of polyhalite (powder, crushed rock and granules) were compared to potassium chl...
Article
No-till soil management is common around the globe, but the impacts on soil structural quality varies depending on cropping practice and inherent soil properties. This study explored water repellency as a driver of soil stabilization, as affected by soil mineralogy, granulometry and organic carbon quality in three Mollisols and one Vertisol under n...
Article
Full-text available
Water storage and flow in shallow subsurface drives runoff generation, vegetation water use and nutrient cycling. Modelling these processes under non-steady state conditions is challenging, particularly in regions like the subtropics that experience extreme wet and dry periods. At the catchment-scale, physically-based equations (e.g., Richards equa...
Article
Full-text available
The use of limited organic resources to build resilience to drought in semi-arid regions was investigated using systems modelling. The study focussed on Halaba in Ethiopia, drawing on biophysical and socioeconomic data obtained from a survey of farms before, during and after the 2015/16 El Niño event. Using a simplified weather dataset to remove no...
Article
Microbial transport in soil affects pathogen retention, colonization, and innoculant delivery in bioremediating agricultural soils. Various bacteria strains residing in the fluid phases of soils are potential contaminants affecting human health.We measured the transport of hydrophilic Escherichia coli (E. coli) and hydrophobic Rhodococcus erythropo...
Article
Full-text available
Subtropical regions have clay-rich, weathered soils, and long dry periods followed by intense rainfall that produces large fluctuations in soil water content (SWC) and hydrological behavior. This complicates predictions of spatio-temporal dynamics, as datasets are typically collected at too coarse resolution and observations often represent a durat...
Article
Full-text available
The use of limited organic resources to build resilience to drought in semi-arid regions was investigated using systems modelling. The study focussed on Halaba in Ethiopia, drawing on biophysical and socio-economic data obtained from a survey of farms before, during and after the 2015/16 El Niño event. Using a simplified weather dataset to remove n...
Article
Plants have a large impact on the physical behaviour of soil, partly due to seed and root exudates that alter mineral:organic matter associations. In this study we explored how the decomposability of residues in soil interacts with seed or root exudate compounds to influence microbial respiration, mechanical behaviour and hydrological properties. S...
Article
Engineered water repellent soils have great potential as construction materials for seepage barriers. By adjusting the water repellency of the soil, an impermeable or semi-permeable seepage barrier can be constructed to suit various engineering applications, such as impervious materials to contain water or semi-permeable materials to allow vegetati...
Article
Full-text available
Aims Rhizodeposits collected from hydroponic solutions with roots of maize and barley, and seed mucilage washed from chia, were added to soil to measure their impact on water retention and hysteresis in a sandy loam soil at a range of concentrations. We test the hypothesis that the effect of plant exudates and mucilages on hydraulic properties of s...
Article
The development of soil sustainability is linked to the improved management of soil biota, such as earthworms, and crop residues to improve soil physical structure, enhance microbial activities, and increase nutrient cycling. This study examined the impacts of maize residue (65.8C/N ratio, dry biomass 0.75 kg m ⁻² ) incorporation and earthworms (70...
Presentation
Full-text available
Polyhalite (K2SO4.MgSO4.2CaSO4.2H2O) is increasingly becoming of interest as a fertilizer with the discovery of the world’s largest resource of over 2.5 billion tonnes in North Yorkshire, UK. The nutrient content of polyhalite from this deposit is 14% K2O, 17% CaO, 6% MgO and 19% S. Important to understanding the agronomic performance of polyhalite...
Article
Root tensile strength controls root reinforcement, but a range of factors including root moisture and diameter have such a large impact that it is difficult to make predictions. In this study, we measured how variable root moisture content affects the relationship between root diameter and root tensile strength of herbaceous plants. Fresh roots of...
Article
Long-term fertilization has a considerable effect on the dynamics of soil organic carbon (SOC). However, quantifying the contribution of fertilization practices to SOC is still a challenge. In this study, we selected a 30-yr fertilization experiment planted with a shift from C 3 to C 4 crops. Our objectives were (i) to determine temporal dynamics o...
Article
Nitrate accumulation has been reported in the top 1 m and subsurface soil (> 1 m) across arid to semi-humid regions, but not in humid regions. Nitrate inventories through the whole regolith, referred to collectively as soil and saprolite, in humid regions have received little attention to date, likely due to previously assumed low nitrification rat...
Article
Full-text available
Soil adjacent to roots has distinct structural and physical properties from bulk soil, affecting water and solute acquisition by plants. Detailed knowledge on how root activity and traits such as root hairs affect the 3D pore structure at a fine scale is scarce and often contradictory. Roots of hairless barley (Hordeum vulgare L. cv ‘Optic’) mutant...
Article
Full-text available
Background and aimsAlternate wetting and drying (AWD) saves water in paddy rice production but could influence soil physical conditions and root growth. This study investigated the interaction between contrasting rice genotypes, soil structure and mechanical impedance influenced by hydraulic stresses typical of AWD. Methods Contrasting rice genotyp...
Poster
Full-text available
Investigating the impact of using polyhalite (commercially known as POLY4) on soils high in sodium.
Poster
Full-text available
Leaching column study investigating the movement of nutrients through the soil from different forms of polyhalite (commercially known as POLY4)
Article
Full-text available
Most water and nutrients essential for plant growth travel across a thin zone of soil at the interface between roots and soil, termed the rhizosphere. Chemicals exuded by plant roots can alter the fluid properties, such as viscosity, of the water phase, potentially with impacts on plant productivity and stress tolerance. In this paper, we study the...
Article
Full-text available
The extent (determined by the repellency indices RI and RIc) and persistence (determined by the water drop penetration time, WDPT) of soil water repellency (SWR) induced by pines were assessed in vastly different geographic regions. The actual SWR characteristics were estimated in situ in clay loam soil at Ciavolo, Italy (CiF), sandy soil at Culbin...
Conference Paper
Plant roots mechanically reinforce the soil due to their tensile strength, whilst extraction of water by roots for transpiration increases soil water suction in the profile and hence increases effective stress. Relatively little is known about the relative effectiveness of different plant species in their ability to mechanically and hydraulically r...
Article
Full-text available
The deposition of organic matter (OM), which is known for its high potential water repellency, on biopore walls can enhance preferential flow through these pores. In this study OM composition determined with DRIFT spectroscopy was related to soil water repellency (SWR) determined with Sessile Drop method (SDM), Wilhelmy-plate method (WPM), and sorp...
Article
Understanding root-reinforcement of vegetated slopes is hindered by the cost and practicality of full scale tests to explore global behaviour at the slope scale, and the idealised nature of smaller-scale testing to date that has relied on model root analogues. In this study we investigated the potential to use living plant roots in small scale expe...
Article
Full-text available
Background and aim: Plant exudates greatly affect the physical behaviour of soil, but measurements of the impact of exudates on compression characteristics are missing. Our aim is to provide these data and explore how plant exudates may enhance the restructuring of compacted soils following cycles of wetting and drying. Methods: Two soils were a...
Article
Full-text available
We hypothesized that plant exudates could either gel or disperse soil depending on their chemical characteristics. Barley (Hordeum vulgare L. cv. Optic) and maize (Zea mays L. cv. Freya) root exudates were collected using an aerated hydroponic method and compared with chia (Salvia hispanica L.) seed exudate, a commonly used root exudate analogue. S...
Poster
Full-text available
Polyhalite is an evaporite mineral with the chemical formula K2SO4.MgSO4.2CaSO4.2H2O. Previous work on granulated polyhalite (POLY4) indicated differences in mechanical behaviour of polyhalite treated soils under laboratory conditions for tensile strength. The current work investigates the effect of polyhalite at the mesocosm scale on the susceptib...
Article
Full-text available
The parameters in Richards’ equation are usually calculated from experimentally measured values of the soil water characteristic curve and saturated hydraulic conductivity. The complex pore structures that often occur in porous media complicate such parametrisation due to hysteresis between wetting and drying and the effects of tortuosity. Rather t...
Article
Full-text available
Using rhizosphere-scale physical measurements we test the hypothesis that plant exudates gel together soil particles and on drying they enhance soil water repellency. Barley and maize root exudates were compared with chia seed exudate, a commonly used root exudate analogue. Sandy loam and clay loam soils were treated with root exudates at 0.46 and...
Data
Fig. S1 Assessment of the WEKA segmentation process. Fig. S2 Normalised cumulative pore size distribution (PSD) over distance from the root surface. Table S1 Performance of iterative WEKA segmentation process Methods S1 Segmentation procedure.
Article
We hypothesized that plant exudates could either gel or disperse soil depending on their chemical characteristics. Barley (Hordeum vulgare L. cv. Optic) and maize (Zea mays L.cv. Freya) root exudates were collected using an aerated hydroponic method and compared to chia (Salvia hispanica L.) seed exudate, a commonly used root exudate analogue. Sand...
Technical Report
Full-text available
Three long term and one newer soil management experiments from eastern Britain were used to answer several key questions relevant for cereal growers. The questions focused on soil physical and chemical conditions (including possible carbon accumulation) for crop growth and comparing cultivar, yield and economic performance under different tillage r...
Article
Full-text available
In this paper, we provide direct evidence of the importance of root hairs on pore structure development at the root–soil interface during the early stage of crop establishment. This was achieved by use of high‐resolution (c. 5 μm) synchrotron radiation computed tomography (SRCT) to visualise both the structure of root hairs and the soil pore struct...
Article
Full-text available
This study used a combined tracer approach of isotopically labelled carbon (C) and rare earth oxides (REO) to determine soil aggregate transfer paths following input of organic matter. A model quantifying aggregate turnover rates over time was verified by a controlled incubation study. Four natural soil aggregate size ranges (<0.053 mm, 0.053–0.25...
Article
Full-text available
Key message: QTL mapping identifies a range of underlying and unrelated genes with apparent roles in raspberry fruit ripening and softening that show characteristic developing fruit expression profiles. Fruit softening is an important agronomical trait that involves a complex interaction of plant cell processes. We have used both qualitative and q...
Article
A stable isotope (¹³C-residue, ¹⁵N-NO3– fertiliser) approach combined with measurements of soil pore space gas concentrations was used to investigate spatial and temporal mechanisms of residue carbon (C) affecting denitrification. Whilst relationships between residue addition and N2O fluxes have previously been well characterised, the influence of...
Conference Paper
Full-text available
The ‘Soil Platforms’ project (AHDB Project 3786 - Platforms to test and demonstrate sustainable soil management: integration of major UK field experiments) works with some of the longest running contemporary UK soil tillage experiments. The four sites within the ‘Soil Platforms’ project are at Mid Pilmore (Perthshire, Scotland, established 2003), t...
Conference Paper
Full-text available
Mouldboard ploughing affects soil bulk density, aeration, drainage, thermal regimes, and soil microorganisms (Sun et al., 2011). Tillage breaks up plant residues, may degrade previously protected organic matter and potentially release CO2 to the atmosphere (Farina et al., 2011). Reduced tillage through either no till or non-inversion tillage to sha...
Conference Paper
Full-text available
Vegetation as a means to improve slope stability is well recognised and incorporated in geotechnical and ecological engineering practice to protect slopes against shallow landslides. Much of the research in this area has quantified root reinforcement of soil shear behaviour at prescribed soil depths in either the laboratory or the field. Costs and...
Article
In many agricultural catchments of Europe and North America, pesticides occur at generally low concentrations with significant temporal variation. This poses several challenges for both monitoring and understanding ecological risks/impacts of these chemicals. This study aimed to compare the performance of passive and spot sampling strategies given...
Article
Full-text available
The remarkable complexity of soil and its importance to a wide range of ecosystem services presents 133 major challenges to the modeling of soil processes. Although major progress in soil models has 134 occurred in the last decades, models of soil processes remain disjointed between disciplines or 135 ecosystem services, with considerable uncertain...
Article
Full-text available
We reviewed soil modeling and the role of soil processes in quantifying ecosystem services. Key challenges were identified and the establishment of a soil modeling consortium to advance soil modeling activities, provide a data-model platform, perform model intercomparison and foster communication amongst Earth science disciplines is proposed.
Article
Full-text available
We reviewed soil modeling and the role of soil processes in quantifying ecosystem services. Key challenges were identified and the establishment of a soil modeling consortium to advance soil modeling activities, provide a data-model platform, perform model intercomparison and foster communication amongst Earth science disciplines is proposed.
Article
Gelifluction, thixotropy and yield stress were measured from < 5 g soil samples taken from Signy, Alectoria, Greenwich, Wiencke and Livingston islands in the maritime Antarctic using a temperature-controlled rotational rheometer. The small sample size that this method permitted is compatible with sampling from sensitive sample locations. An oscilla...