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Background and aim: Soil structure is an important indicator of the quality of soil, but detecting the early signs of soil degradation from soil structure is difficult. Developing precise instruments able to diagnose soil structure quickly is therefore critical to improve management practices. Here, the objective is to develop an instrument analysing the roughness of surfaces resulting from the fracture of soil cores, and to test the instrument's ability to detect changes in soil structure cause by crop type and tillage. We have designed and constructed a 3D laser profilometer suitable for analysing standard soil cores. The 3D soil profiles were first assembled into a 3D surface using image analysis before roughness indicators could be computed. The method was tested by analysing how soil surface roughness was affected by crop varieties (barley and bean) and tillage (conventional tillage and no tillage). Results showed the method is precise and could reliably detect an influence of crop type and tillage on the roughness indicator. It was also observed that tillage reduced the difference in soil structure between the different cultures. Also, the soil in which barley grew had significantly lower roughness, irrespective of the tillage method. This could indicate that the roughness indicator is affected by biopores created by the root system. In conclusion, roughness indicators obtained from the fracture of soil cores can be easily obtained by laser profilometry and could offer a reliable method for assessing the effect of crop types and soil management on soil quality. [ABSTRACT FROM AUTHOR]

Intercropping is a farming practice involving two or more crop species, or genotypes, growing together and coexisting for a time. On the fringes of modern intensive agriculture, intercropping is important in many subsistence or low-input/resource-limited agricultural systems. By allowing genuine yield gains without increased inputs, or greater stability of yield with decreased inputs, intercropping could be one route to delivering 'sustainable intensification'. We discuss how recent knowledge from agronomy, plant physiology and ecology can be combined with the aim of improving intercropping systems. Recent advances in agronomy and plant physiology include better understanding of the mechanisms of interactions between crop genotypes and species - for example, enhanced resource availability through niche complementarity. Ecological advances include better understanding of the context-dependency of interactions, the mechanisms behind disease and pest avoidance, the links between above- and below-ground systems, and the role of microtopographic variation in coexistence. This improved understanding can guide approaches for improving intercropping systems, including breeding crops for intercropping. Although such advances can help to improve intercropping systems, we suggest that other topics also need addressing. These include better assessment of the wider benefits of intercropping in terms of multiple ecosystem services, collaboration with agricultural engineering, and more effective interdisciplinary research. [ABSTRACT FROM AUTHOR]

To penetrate soil, a root requires pressure both to expand the cavity it is to occupy, σn, and to overcome root-soil friction, σf. Difficulties in estimating these two pressures independently have limited our ability to estimate the coefficient of soil-root friction, μsr. We used a rotated penetrometer probe, of similar dimensions to a root, and for the first time entering the soil at a similar rate to a root tip, to estimate σn. Separately we measured root penetration resistance (PR) Qr. Root PR was between two to four times σn. We estimated that the coefficient of root-soil friction ( μsr) was 0.21-0.26, based on the geometry of the root tip. This is slightly larger than the 0.05-0.15 characteristic of boundary lubricants. Scanning electron microscopy showed that turgid border cells lined the root channel, supporting our hypothesis that the lubricant consisted of mucilage sandwiched between border cells and the surface of the root cap and epidermis. This cell-cell lubrication greatly decreased the friction that would otherwise be experienced had the surface of the root proper slid directly past unlubricated soil particles. Because root-soil friction can be a substantial component of root PR, successful manipulation of friction represents a promising opportunity for improving plant performance. [ABSTRACT FROM AUTHOR]

Within-year changes in parameters of the single-porosity van Genuchten model and the dual-porosity bi-exponential model for water retention characteristics were determined for a shallow Entisol in farmland and forestland. Tension infiltration data showed that soil macropores were the main contributing pores to fast drainage under both land uses in the rainy summer. For regions with shallow soils underlain by fractured parent rocks, it is important to understand the characteristics of soil water retention and hydraulic conductivity. This knowledge could support the development of strategies to manage water for crops. A farmland and a forestland with thin Entisols, located in hilly central Sichuan on the Yangtze River's upper reaches, were chosen as experimental fields. A variety of parameters related to hydraulically effective macroporosity (pore radius >125 µm), the single-porosity van Genuchten model, and the dual-porosity bi-exponential (BE) model for water retention characteristics were determined. Tension infiltration data showed that soil macropores were the main pores (accounting for 87.9-99.7%) contributing to fast drainage at all tested soil depths under both land uses in the rainy summer, in spite of their very low percentage of the total porosity (0.61-3.06%). The available soil water content, determined as the drainable soil textural porosity using the bi-exponential model (ϑtxt-BE), was found to be very low (0.032-0.091 m³ m-3) and negatively (P < 0.05) related to the initial soil water content at the time of sampling, resulting in high vulnerability of the crops grown on the farmland to drought. Plowing operations and periodical drying appeared to be the two main factors controlling the within-year change in soil hydraulic properties. For agricultural soils showing a bimodal pore size distribution, the soil's capacity to hold crop-available water in textural pores, which may vary with the time of year, rather than the total soil water content should be analyzed to inform decisions on irrigation operations including required amounts. [ABSTRACT FROM AUTHOR]