Sarah J. Dunham

Enhanced weathering of silicate rocks in agriculture is an option for atmospheric CO₂ removal and fertility improvement. The objective of our work is to characterise some of the agricultural consequences of a basaltic powder amendment on soil-crop systems. Two doses of basalt (80 and 160 t ha⁻¹) were applied to two types of slightly acid soils (sandy or silty clayey), derived from long-term trials at Bordeaux (INRAE, France) and Rothamsted Research (England), respectively. For each soil, half of the pots were planted with ryegrass; the other half were left bare. Thus, the experiment had twelve treatments with four replications per treatment. Soil pH increased with the addition of basalt (+0.8 unit), with a 5% equivalence of that of reactive chalk. The basalt contained macro- and micronutrients. Some cations extractable in the basalt before being mixed to the soil became more extractable with increased weathering, independent of plant cover. Plant uptake generally increased for macronutrients and decreased for micronutrients, due to increased stock (macro) and reduced availability (micronutrients and P), related to pH increases. K supplied in the basalt was responsible for a significant increase in plant yield on the sandy soil, linked to an average basalt K utilisation efficiency of 33%. Our general conclusion is that rock dust applications have to be re-evaluated at each site with differing soil characteristics.

The phosphorus (P) supply from soils is crucial to crop production. Given the complexity involved in P-cycling, a model that can simulate the major P-cycling processes and link with other nutrients and environmental factors, e.g., soil temperature and moisture, would be a useful tool. The aim of this study was to describe a process-based P module added to the SPACSYS (Soil Plant and Atmosphere Continuum System) model and to evaluate its predictive capability on the dynamics of P content in crops and the impact of soil P status on crop growth. A P-cycling module was developed and linked to other modules included in the SPACSYS model. We used a winter wheat (Triticum aestivum, cv Xi-19) field experiment at Rothamsted Research in Harpenden to calibrate and validate the model. Model performance statistics show that the model simulated aboveground dry matter, P accumulation and soil moisture dynamics reasonably well. Simulated dynamics of soil nitrate and ammonium were close to the observed data when P fertiliser was applied. However, there are large discrepancies in fields without P fertiliser. This study demonstrated that the SPACSYS model was able to investigate the interactions between carbon, nitrogen, P and water in a single process-based model after the tested P module was implemented.

Food can be an important source of inorganic As for human intake. Recent studies have focused on rice, while little information is available on As accumulation, distribution, and speciation in wheat, which is the second most important food grain cereal. Grain samples of 26 wheat cultivars grown in five field trials located in productive farming regions in Europe were therefore analyzed for As concentration and speciation. Grain from four trials contained low concentrations of total As (7.7 ± 5.4 μg kg⁻¹), reflecting low levels of As in the soils (1.3−11 mg kg⁻¹). In contrast, at one of the trial sites the As level in the soil was greater (29 mg kg⁻¹), and much higher As concentrations (69 ± 17 μg kg⁻¹) were present in the wheat grain. Milling of wheat grain into bran and white flour fraction showed the concentration of As in the bran, with a 3.8−4.7-fold higher As concentration than in the white flour. Two methods (a phosphate buffer solution and 1% HNO₃) were used to extract As species from wholemeal, bran, and white flour of wheat, with average extraction efficiencies of 65% and 88%, respectively. Only inorganic As was found in the extracts, with no methylated As being detected. The contribution of wheat to human intake of inorganic As is small for wheat crops grown in uncontaminated soils but becomes significant for those grown in soils with elevated As. In the latter case, milling can be used to reduce the As concentration in the white flour.

• Arabidopsis halleri is a well-known zinc (Zn) hyperaccumulator, but its status as a cadmium (Cd) hyperaccumulator is less certain. Here, we investigated whether A. halleri can hyperaccumulate Cd and whether Cd is transported via the Zn pathway. • Growth and Cd and Zn uptake were determined in hydroponic experiments with different Cd and Zn concentrations. Short-term uptake and root-to-shoot transport were measured with radioactive ¹⁰⁹Cd and ⁶⁵Zn labelling. • A. halleri accumulated > 1000 mg Cd kg⁻¹ in shoot dry weight at external Cd concentrations ≥ 5 µm, but the short-term uptake rate of ¹⁰⁹Cd was much lower than that of ⁶⁵Zn. Zinc inhibited short-term ¹⁰⁹Cd uptake kinetics and root-to-shoot translocation, as well as long-term Cd accumulation in shoots. Uptake of ¹⁰⁹Cd and ⁶⁵Zn were up-regulated, respectively, by low iron (Fe) or Zn status. A. halleri was much less tolerant to Cd than to Zn. • We conclude that A. halleri is able to hyperaccumulate Cd partly, at least, through the Zn pathway, but the mechanisms responsible for cellular Zn tolerance cannot detoxify Cd effectively.

Summary: Pteris vittata was the first identified arsenic (As) hyperaccumulator. Our aim was to test whether As hyperaccumulation occurs in other fern species, and whether P. vittata collected from both contaminated and uncontaminated environments accumulates As similarly. Three accessions of P. vittata , two cultivars of Pteris cretica , Pteris longifolia and Pteris umbrosa were grown with 0–500 mg As kg ⁻¹ added to the substrate. A second experiment compared As uptake by five common ferns obtained from commercial suppliers. The results show that, in addition to P. vittata , P. cretica , P. longifolia and P. umbrosa also hyperaccumulate As to a similar extent. There was little difference between different Pteris species, or between different accessions of P. vittata . By contrast, Asplenium nidus , Davallia canarensis , Polypodium aureum , Polystichum tsus‐simense do not hyperaccumulate As. This study identified three new species of As hyperaccumulators in the Pteris genus and suggests that As hyperaccumulation is a constitutive property in P. vittata .

A pot experiment was conducted to compare two strategies of phytoremediation: natural phytoextraction using the Zn and Cd hyperaccumulator Thlaspi caerulescens J. Presl & C. Presl versus chemically enhanced phytoextraction using maize (Zea mays L.) treated with ethylenediaminetetraacetic acid (EDTA). The study used an industrially contaminated soil and an agricultural soil contaminated with metals from sewage sludge. Three crops of T. caerulescens grown over 391 d removed more than 8 mg kg⁻¹ Cd and 200 mg kg⁻¹ Zn from the industrially contaminated soil, representing 43 and 7% of the two metals in the soil. In contrast, the high concentration of Cu in the agricultural soil severely reduced the growth of T. caerulescens, thus limiting its phytoextraction potential. The EDTA treatment greatly increased the solubility of heavy metals in both soils, but this did not result in a large increase in metal concentrations in the maize shoots. Phytoextraction of Cd and Zn by maize + EDTA was much smaller than that by T. caerulescens from the industrially contaminated soil, and was either smaller (Cd) or similar (Zn) from the agricultural soil. After EDTA treatment, soluble heavy metals in soil pore water occurred mainly as metal–EDTA complexes, which were persistent for several weeks. High concentrations of heavy metals in soil pore water after EDTA treatment could pose an environmental risk in the form of ground water contamination.