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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 experimentally elucidate some of the impacts that root hairs have on plant performance on a field scale. Methods A field experiment was set up in Scotland for two consecutive years, under contrasting climate conditions and different soil textures (i.e. clay loam vs. sandy loam). Five barley (Hordeum vulgare) genotypes exhibiting variation in root hair length and density were used in the study. Root hair length, density and rhizosheath weight were measured at several growth stages, as well as shoot biomass, plant water status, shoot phosphorus (P) accumulation and grain yield. Key Results Measurements of root hair density, length and its correlation with rhizosheath weight highlighted trait robustness in the field under variable environmental conditions, although significant variations were found between soil textures as the growing season progressed. Root hairs did not confer a notable advantage to barley under optimal conditions, but under soil water deficit root hairs enhanced plant water status and stress tolerance resulting in less negative leaf water potential and lower leaf abscisic acid concentration, while promoting shoot P accumulation. Furthermore, the presence of root hairs did not decrease yield under optimal conditions, while root hairs enhanced yield stability under drought. Conclusions Selecting for beneficial root hair traits can enhance yield stability without diminishing yield potential, overcoming the breeder’s dilemma of trying to simultaneously enhance both productivity and resilience. Therefore, the maintenance or enhancement of root hairs can represent a key trait for breeding the next generation of crops for improved drought tolerance in relation to climate change.

This article describes the phenomenon of soil water repellency, starting from the fundamental principals of water transport and storage in soil. Soil water repellency is a reduction in the rate of wetting and retention of water in soil caused by the presence of hydrophobic coatings on soil particles. For crop production and the maintenance of amenity turf, water repellency can stress plants resulting in poorer yield quality or grass 'playability' , respectively. The biological causes of water repellency, primarily the influence of fungi, will be discussed, as an understanding of the source of the problem will be beneficial in developing solutions. Exacerbation of repellency through climate change and the use of 'engineered' soils for amenity surfaces will be demonstrated using research findings from around the globe. In developing solutions to soil water repellency, its positive benefits, if maintained at very low levels, need to be considered. Water repellency is a key process in the physical stabilisation of soil and its impact on evaporation also needs to be considered. Before developing a rapid solution to repellency based only on water transport rates, a holistic understanding of the impacts on soil water relations is essential.

Soil degradation is a worsening global phenomenon driven by socio‐economic pressures, poor land management practices and climate change. A deterioration of soil structure at timescales ranging from seconds to centuries is implicated in most forms of soil degradation including the depletion of nutrients and organic matter, erosion and compaction. New soil–crop models that could account for soil structure dynamics at decadal to centennial timescales would provide insights into the relative importance of the various underlying physical (e.g. tillage, traffic compaction, swell/shrink and freeze/thaw) and biological (e.g. plant root growth, soil microbial and faunal activity) mechanisms, their impacts on soil hydrological processes and plant growth, as well as the relevant timescales of soil degradation and recovery. However, the development of such a model remains a challenge due to the enormous complexity of the interactions in the soil–plant system. In this paper, we focus on the impacts of biological processes on soil structure dynamics, especially the growth of plant roots and the activity of soil fauna and microorganisms. We first define what we mean by soil structure and then review current understanding of how these biological agents impact soil structure. We then develop a new framework for modelling soil structure dynamics, which is designed to be compatible with soil–crop models that operate at the soil profile scale and for long temporal scales (i.e. decades, centuries). We illustrate the modelling concept with a case study on the role of root growth and earthworm bioturbation in restoring the structure of a severely compacted soil.

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 no-till management and with different levels of cropping intensity. The studied soils were located along a west-east textural gradient in the northern part of the Pampean region of Argentina. Cropping intensity treatments evaluated in each one of the soils were: Poor Agricultural Practices (PAP) close to a monoculture, Good Agricultural Practices (GAP) involving a diverse crop rotation and more targeted inputs, and the soil in the surrounding natural environment (NE) as a reference. NE had the greatest aggregate stability (MWD) of all cropping intensities, with GAP being more stable than PAP for Mollisols and PAP being greater than GAP for the Vertisol. This trend matched the Repellency Index (R index), with greater R index associated with greater MWD, including the difference between the Mollisols and Vertisol. However, the persistence of water repellency, measured by the Water Drop Penetration Time (WDPT) test followed the trend NE > GAP > PAP regardless of soil type. The increases in R index and MWD were related to higher intensification as measured by the Crop Sequence Index, and decreased with greater soybean occurrence in the sequence. Both WDPT and R index were closely related to aggregate stability, particularly for Mollisols. These results highlight the importance of considering the inherent soil characteristics texture and mineralogy to understand aggregate stabilization mediated by water repellency. Good correlations between soil water repellency, organic carbon fractions and aggregate stability were found. Under no-till, crop rotations can be altered to increase soil stability by inducing greater water repellency in the soils. The findings suggest that water repellency is a major property influencing soil structure stabilization, thus providing a useful quality indicator.