The research was carried out to determine the effect of basin‐based conservation agriculture (CA) on selected soil quality parameters. Paired plots (0.01 ha) of CA and conventional tillage based on the animal‐drawn mouldboard plough (CONV) were established between 2004 and 2007 on farm fields on soils with either low (12–18% – sandy loams and sandy clay loams) or high clay levels (>18–46% – sandy clays and clays) as part of an ongoing project promoting CA in six districts in the smallholder farming areas of Zimbabwe. We hypothesized that CA would improve soil organic carbon (SOC), bulk density, aggregate stability, soil moisture retention and infiltration rate. Soil samples for SOC and aggregate stability were taken from 0 to 15 cm depth and for bulk density and soil moisture retention from 0 to 5, 5 to 10 and 10 to 15 cm depths in 2011 from maize plots. Larger SOC contents, SOC stocks and improved aggregate stability, decreased bulk density, increased pore volume and moisture retention were observed in CA treatments. Results were consistent with the hypothesis, and we conclude that CA improves soil quality under smallholder farming. Benefits were, however, greater in high clay soils, which is relevant to the targeting of practices on smallholder farming areas of sub‐Saharan Africa.

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Toxic trace element (TTE) contamination in urban soils may pose potential health risks, especially in cities with previous industrial activities. This study aimed to investigate soil contamination in urban allotments in Sheffield, the uptake of TTEs in autumn and spring sown onions (Allium cepa), and their potential risks on human health via consumption of the crops. Paired soil and plant samples were taken in triplicates from four private allotments to assess potentially elevated levels of lead (Pb), zinc (Zn), copper (Cu), arsenic (As), and chromium (Cr). These elements in soils exceeded the ambient background levels for England. Both Pb and As exceeded some UK and EU soil tolerable limits. Concentration factors (CF) were calculated as the ratio of trace element in the plant as compared to that in the soil, and uptake rates were in the order Zn>Cu>Cr>Pb>As. Concentrations were higher for most TTEs in spring sown onions (SSO), and had significantly higher CF (p<0.05) for Pb and Cr than autumn sown onions (ASO), whereas the opposite was true for As. Toxic elements in plants did not exceed FAO/WHO intake limits when considering TTE content per plant and consumption rates. Human health risk assessment calculations using target hazard quotients (THQ) and hazard indexes (HI) indicated that consuming onions alone did not pose an immediate health risk.

Non-invasive techniques are essential to deepen our understanding of root-soil interactions in situ. Neutron computed tomography (NCT) is an example of such techniques that have been successfully used to study these interactions in high resolution. Many of the studies using NCT however, have invariably focused on lupine plants and thus there is limited information available on other more commercially important staple crop plants such as wheat and rice. Also considering the high neutron sensitivity to hydrogen (e.g. water in roots or soil organic matter), nearly all previous in-situ NCT studies have used a relatively homogeneous porous media such as sand, low in soil organic matter and free from soil aggregates, to obtain highquality images. However to expand the scope of the use of NCT to other more commercially important crops and in less homogenous soils, in this study we focused on wheat root growth in a soil that contained a considerable amount of soil organic matter (SOM) and different sized aggregates. As such, the main aims of this research were (1) to unravel wheat (Triticum aestivum cv. Fielder) root system architecture (RSA) when grown in an aggregated sandy loam soil (<4 mm) with 4% SOM content, (2) Map in 3D, soil water distribution after a brief drying period and (3) to understand how the root system interacts with soil moisture 2 distribution brought about by soil structural heterogeneity. To achieve these, wheat seedlings were grown for 13-days in aluminium tubes (100 mm height and 18 mm diameter) packed with soil and imaged for the first time at the IMAT neutron beamline (in the Rutherford Appleton Laboratory, UK). To the best of our knowledge, this is also the first study to use NCT to study wheat root architectural development. Our study proved that NCT can successfully be used to reveal wheat RSA in a heterogeneous aggregated soils with moderate amounts of SOM. Lateral root growth within the soil column was increased in regions with increased finer soil separates. NCT was also able to successfully map water distribution in a 3D and we show that large macro-aggregates preferentially retained relatively higher soil moisture in comparison to the smaller soil separates within our samples (Fig. 1). This highlights the importance large macro-aggregates in sustainable soil management as they may be able to provide plants water during periodic dry spells. More in situ investigations are required to further understand the impact of different aggregate sizes on RSA and water uptake. Figure 1: NCT image of a 13-day old wheat seedling root growing in an aggregated sandy loam soil. The colour map indicates water distribution within the soil column.

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