Portable X-ray fluorescence (pXRF) calibration for analysis of nutrient concentrations and trace element contaminants in fertilisers.

With the increasing popularity of local blending of fertilisers, the fertiliser industry faces issues regarding quality control and fertiliser adulteration. Another problem is the contamination of fertilisers with trace elements that have been shown to subsequently accumulate in the soil and be taken up by plants, posing a danger to the environment and human health. Conventional characterisation methods necessary to ensure the quality of fertilisers and to comply with local regulations are costly, time consuming and sometimes not even accessible. Alternatively, using a wide range of unamended and intentionally amended fertilisers this study developed empirical calibrations for a portable handheld X-ray fluorescence (pXRF) spectrometer, determined the reliability for estimating the macro and micro nutrients and evaluated the use of the pXRF for the high-throughput detection of trace element contaminants in fertilisers. The models developed using pXRF for Mg, P, S, K, Ca, Mn, Fe, Zn and Mo had R2 values greater or equal to 0.97. These models also performed well on validation, with R2 values greater or equal to 0.97 (except for Fe, R2val = 0.55) and slope values ranging from 0.81 to 1.44. A second set of models were developed with a focus on trace elements in amended fertilisers. The R2 values of calibration for Co, Ni, As, Se, Cd and Pb were greater than or equal to 0.80. At concentrations up to 1000 mg kg-1, good validation statistics were also obtained; R2 values ranged from 0.97-0.99, except in one instance. The regression coefficients of the validation also had good prediction in the range of 0-100 mg kg-1 (R2 values were from 0.78-0.99), but not as well at lower concentrations up to 20 mg kg-1 (R2 values ranged from 0.10-0.99), especially for Cd. This study has demonstrated that pXRF can measure several major (P, Ca) and micro (Mn, Fe, Cu) nutrients, as well as trace elements and potential contaminants (Cr, Ni, As) in fertilisers with high accuracy and precision. The results obtained in this study is good, especially considering that loose powders were scanned for a maximum of 90 seconds without the use of a vacuum pump.

Plant Available Zinc Is Influenced by Landscape Position in the Amhara Region, Ethiopia.

Zinc (Zn) is an important element determining the grain quality of staple food crops and deficient in many Ethiopian soils. However, farming systems are highly variable in Ethiopia due to different soil types and landscape cropping positions. Zinc availability and uptake by plants from soil and fertilizer sources are governed by the retention and release potential of the soil, usually termed as adsorption and desorption, respectively. The aim of this study was to characterize the amount of plant available Zn at different landscape positions. During the 2018/19 cropping season, adsorption-desorption studies were carried out on soil samples collected from on-farm trials conducted at Aba Gerima, Debre Mewi and Markuma in the Amhara Region. In all locations and landscape positions, adsorption and desorption increased with increasing Zn additions. The amount of adsorption and desorption was highly associated with the soil pH, the soil organic carbon concentration and cation exchange capacity, and these factors are linked to landscape positions. The Freundlich isotherm fitted very well to Zn adsorption (r2 0.87-0.99) and desorption (r2 0.92-0.99), while the Langmuir isotherm only fitted to Zn desorption (r2 0.70-0.93). Multiple regression models developed by determining the most influential soil parameters for Zn availability could be used to inform Zn fertilizer management strategies for different locations and landscape positions in this region, and thereby improve plant Zn use efficiency.

A comparison of soil texture measurements using mid-infrared spectroscopy (MIRS) and laser diffraction analysis (LDA) in diverse soils.

Spectroscopic methods for the determination of soil texture are faster and cheaper than the standard methods, but how do the results compare? To address this question, laser diffraction analysis (LDA) and mid-infrared spectroscopy (MIRS) analysis have been compared to conventional sieve-pipette measurements of texture in diverse European and Kenyan soils. To our knowledge this comparison between LDA and MIRS has not been made previously. It has used soils with a broad range of organic carbon (OC) contents to investigate whether, as in other techniques, clay-OC aggregation affects the estimation of clay with MIRS. The MIRS predictions of clay content were much better than the LDA measurements, but both techniques gave good measurements of sand content. The MIRS over-estimated clay at low clay content and under-estimated at high clay content (calibration set R2 = 0.83). The LDA over-estimated clay by ~ 60% (calibration set R2 = 0.36), indicating that the widely used clay threshold of < 8 µm was too high, and < 4 µm was found to be more accurate. In samples with < 5% OC content, both the LDA and MIRS gave very good clay predictions (R2 = 0.88 and 0.81, respectively). But in predictions of clay content in samples with > 5% OC the LDA under-estimated (R2 = < 0.1) and MIRS over-estimated (R2 = 0.34) clay content. In soils with OC removed, the MIRS prediction of clay content improved, indicating interference between over-lapping spectral regions for organic and mineral constituents. Unlike granulometric measurements of texture such as the LDA, MIRS analysis is not subject to the limitations imposed by the shape and density of particles. It was concluded that in typical agricultural soils with < 5% OC and < 60% clay content, both techniques could be used for cheap, fast and reliable estimates of soil texture.

Simulation of Phosphorus Chemistry, Uptake and Utilisation by Winter Wheat.

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.

Differences in EDTA-assisted metal phytoextraction between metallicolous and non-metallicolous accessions of Rumex acetosa L.

Two common sorrel (Rumex acetosa) accessions, one from a Zn-Pb contaminated site (CS accession) and the other from an uncontaminated site (UCS accession), were hydroponically exposed to a mixture of heavy metals (Pb(2+) + Zn(2+) + Cd(2+)) with and without EDTA at an equimolar rate. The metallicolous CS accession showed a higher tolerance to metal treatment in the absence of the chelating agent, whereas the UCS accession was especially tolerant to EDTA treatment alone. Combination of metal and EDTA treatment resulted in a higher Pb accumulation in shoots of both accessions although plants hardly showed phytotoxic symptoms. Cd and Zn uptake was not augmented by EDTA addition to the polymetallic medium. Chelant-assisted Pb accumulation was 70% higher in the CS accession than in the UCS accession, despite the fact that the former accession evapotranspired less water than the UCS accession. These results support the existence of a non-selective apoplastic transport of metal chelates by R. acetosa roots, not related to transpiration stream.

Effects of chelates on plants and soil microbial community: comparison of EDTA and EDDS for lead phytoextraction.

Most studies on chelate-induced phytoextraction have focused on EDTA-mediated Pb phytoextraction. But EDTA and the formed EDTA-Pb complexes have low biodegradability and high solubility in soil, resulting in an elevated risk of adverse environmental effects. EDDS is an easily biodegradable chelating agent that has recently been proposed as an environmentally sound alternative to EDTA. Consequently, a greenhouse experiment, using a completely randomized factorial design with four replications, was carried out to compare the potential of EDTA and EDDS for chelate-induced Pb phytoextraction with Cynara cardunculus, as well as to investigate the toxicity of these two chelates to both cardoon plants and soil microorganisms. The effects of chelate addition on soil microbial communities were studied through the determination of a variety of biological indicators of soil quality such as soil enzyme activities, basal and substrate-induced respiration, potentially mineralizable nitrogen, and community level physiological profiles. EDTA was much more efficient than EDDS for the enhancement of root Pb uptake and root-to-shoot Pb translocation. In a soil polluted with 5000 mg Pb kg(-1), as a result of the addition of 1 g EDTA kg(-1) soil, a value of 1332 mg Pb kg(-1) DW shoot was obtained. EDDS application resulted in a shoot Pb accumulation of only 310 mg kg(-1)DW. Plants treated with EDDS showed lower values of biomass than those treated with EDTA. EDDS proved to be rapidly degraded, and less toxic to the soil microbial community in control non-polluted soils. Pb-polluted EDDS-treated soils showed significantly higher values of basal and substrate-induced respiration than those treated with EDTA. Although EDDS had a lower capacity to enhance Pb phytoextraction than EDTA, it has the advantage of rapid biodegradation.

Assessment of the phytoextraction potential of high biomass crop plants.

A hydroponic screening method was used to identify high biomass crop plants with the ability to accumulate metals. Highest values of shoot accumulation were found in maize cv. Ranchero, rapeseed cv. Karat, and cardoon cv. Peralta for Pb (18 753 mg kg(-1)), Zn (10 916 mg kg(-1)), and Cd (242 mg kg(-1)), respectively. Subsequently, we tested the potential of these three cultivars for the phytoextraction of a metal spiked compost, finding out that, in cardoon and maize plants, increasing Zn and Cd concentrations led to lower values of root and shoot DW. By contrast, rapeseed shoot growth was not significantly affected by Cd concentration. Finally, a metal polluted soil was used to check these cultivars' phytoextraction capacity. Although the soil was phytotoxic enough to prevent the growth of cardoon and rapeseed plants, maize plants phytoextracted 3.7 mg Zn pot(-1). We concluded that the phytoextraction performance of cultivars varies depending on the screening method used.

Chelate-induced phytoextraction of metal polluted soils with Brachiaria decumbens.

Chelate-induced phytoextraction with high biomass plant species has been proposed for the clean-up of heavy metal polluted soils. In the current work, the effect of the application of two different chelating agents, i.e. EDTA and EDDS, on the metal phytoextraction capacity of Brachiaria decumbens was studied. Although EDTA was, in general, more effective in soil metal solubilization, EDDS, a chelate less harmful to the environment, was more efficient inducing metal accumulation in B. decumbens shoots than EDTA. Indeed, in a moderately heavy metal polluted soil, EDDS caused a 2.54, 2.74 and 4.30-fold increase in Cd, Zn, and Pb shoot metal concentration, respectively, as compared to control plants. In this same soil, EDTA caused a 1.77, 1.11 and 1.87-fold increase in Cd, Zn, and Pb shoot metal concentration, respectively, as compared to control plants. EDDS was also more effective than EDTA in stimulating the translocation of metals from roots to shoots. B. decumbens plants were able to grow in the metal polluted soils showing no visible symptoms of phytotoxicity, which suggests their metal tolerance. Finally, B. decumbens, a fast-growing, high biomass, aluminum tolerant plant species, that has a well-established agronomic system, fulfills most of the requirements for chemically-induced phytoextraction.

Plants against the global epidemic of arsenic poisoning.

Due to the growing current trend around the world of drinking water from underground sources, in an attempt to replace heavily polluted surface water supplies, arsenic is causing a global epidemic of poisoning with hundreds of millions of people now being thought at serious risk in many countries. Phytoremediation (bioremediation mediated by plants) has been proposed as an effective tool in arsenic cleanup. Actually, some plants (most notably, the Chinese brake fern Pteris vittata) have been reported to be suitable for arsenic phytoremediation. In this respect, transgenic plants are being developed to improve their capacity to accumulate arsenic. Most interestingly, rhizofiltration (use of plants to absorb or adsorb pollutants from water) is being considered for the ex situ and in situ remediation of arsenic-contaminated water. Similarly, some plants show great potential to remove arsenic from polluted soil.

Phytoremediation: a technology using green plants to remove contaminants from polluted areas.

Phytoremediation is an emerging cost-effective, non-intrusive, esthetically pleasing, and low cost technology using the remarkable ability of plants to concentrate elements and compounds from the environment and to metabolize various molecules in their tissues. Phytoremediation technology is applicable to a broad range of contaminants, including metals and radionuclides, as well as organic compounds like chlorinated solvents, polychlorobiphenyls, polycyclic aromatic hydrocarbons, pesticides/insecticides, explosives, and surfactants. The use of plants to transport and concentrate metals from the soil into the harvestable parts of roots and above-ground shoots, usually called 'phytoextraction', has appeared on the scene as a valid alternative to traditional physicochemical remediation methods that do not provide acceptable solutions for the removal of metals from soils. Positive results are becoming available regarding the ability of plants to degrade certain organic compounds. Nonetheless, despite the firm establishment of phytoremediation technology in the literature and in extensive research study and in small-scale demonstrations, full-scale applications are currently limited to a small number of projects. At present, the phytoremediation of metal pollutants from the environment could be approaching commercialization.