Green manure and long-term fertilization effects on soil zinc and cadmium availability and uptake by wheat (Triticum aestivum L.) at different growth stages

Fumigation alters the manganese-oxidizing microbial communities to enhance soil manganese availability and increase tomato yield

Manganese is one of the essential trace elements for plants to maintain normal life activities. Soil fumigation, while effectively controlling soil-borne diseases, can also improve the cycling of soil nutrient elements. MiSeq amplicon sequencing is used to determine the composition of soil microbial communities, and structural equation modeling and the random forest algorithm are employed to conduct a correlation analysis between key manganese-oxidizing microorganisms and soil manganese availability. This experiment investigated the microbial mechanisms behind the observed increase in available manganese in soil after fumigation. The key findings revealed that Bacillus, GeoBacillus, GraciliBacillus, Chungangia, and Pseudoxanthomonas play crucial roles in influencing the variation in soil available manganese content. Fumigation was found to elevate the abundance of Bacillus. Moreover, laccase activity emerged as another significant factor impacting soil manganese availability, showing an indirect correlation with available manganese content and contributing to 58 % of the observed variation in available manganese content. In summary, alterations in the communities of manganese-oxidizing microorganisms following soil fumigation are pivotal for enhancing soil manganese availability.

Natural ageing of biochar improves its benefits to soil Pb immobilization and reduction in soil phytotoxicity

Amendments are good tools for immobilizing metal(loid) and improving phytoremediation success. However, the amendment effect is variable and depends on multiple parameters, including amendment type and ageing. Such an ageing effect is rarely studied. Our study is one of the first focusing on how biochar storage affects its effect on soil properties and metal(loid) immobilization, when biochar was applied alone or in combination with green manure. To answer this, a 33-day pot incubation experiment was set up using contaminated soil, amended with two biochars (differing in ages: old (Bo) and new (Bn)) and/or two green manures (leaves of clover or poplar) and sown with Phaseolus vulgaris (bioindicator plant). Soil pore waters, plant growth and metal(loid) accumulation were evaluated. Biochar reduced soil acidity (Bn: + 0.75 pH unit, Bo: + 0.72 unit) and Pb mobility (Bn: - 42%, Bo: - 50%), while green manures acidified the soil (- 0.30 pH unit) and immobilized Pb only after 10 days (- 44%). All amendments reduced soil phytotoxicity. Moreover, the biochar stored at room temperature for a few years demonstrated better abilities to improve soil properties, particularly for Pb immobilization, than the biochar freshly prepared. Finally, as mixtures maturated, soil parameters changed until about ten days, then tended to stabilize. Therefore, it can be concluded that (1) biochar storage will affect its chemical properties and ameliorate its effects, (2) biochar can ameliorate soil properties and immobilize metal(loid)s, while green manures tended to have adverse effects at first, and (3) soil/amendment mixtures should be left to mature about two weeks before potential plant implementation.

Appraising growth, daily intake, health risk index, and pollution load of Zn in wheat (Triticum aestivum L.) grown in soil differentially spiked with zinc

Zinc (Zn) is a vital nutrient element required for plants normal growth and development. It performs imperative functions in numerous metabolic pathways in the plants. However, potentially noxious levels of Zn in terrestrial environment can lead to inhibited photosynthesis, growth, respiratory rate and imbalanced mineral nutrition. In micronutrient malnutrition, Zn deficiency is a global human health problem owing to the human dependence on cereals grains especially wheat-based diet. Therefore, this study investigated the Zn uptake efficacy in Triticum aestivum that is grown under two different doses (100 g/kg or 200 g/kg) of various soil amendments in both pot and field experimentation. Results of this study revealed that mean Zn concentration in different wheat varieties and treatments were varied from 1.53 to 6.03 mg/kg, 11.27 to 40.65 mg/kg, 11.28 to 39.93 mg/kg, and 11.32 to 37.70 mg/kg in amended soil, root, shoot, and grains, respectively. All observed Zn values in soil and wheat parts were lower than the FAO/WHO standards. Zinc values observed for pollution load index (0.034-0.134 mg/kg), daily intake (0.00492-0.01533 mg/kg), and health risk (0.0164-0.0570 mg/kg) index were lower than 1 except bio-concentration factor. Bio-concentration factor (5.076-10.165 mg/kg) revealed that DHARABI-11 variety showed maximum Zn uptake efficacy in farmyard manure treatment. The daily intake and health risk index values also showed that Zn level in grains is safe for inhabitants consumption. Overall, study recommended that these organic amendments are a good source of fertilizers, essentially required for the sustainable management of soil and increases the Zn accumulation in wheat grains which can ultimately reduce the Zn malnutrition in human food chain.

A comparison study of physiological response and TaZIPs expression in seedlings of two wheat (Triticum aestivum L.) cultivars with contrasting grain zinc accumulation

Screening and breeding of high-Zn-accumulating wheat cultivars have received increasing attention in recent years. However, the exact mechanism of Zn uptake and accumulation in wheat is not fully understood. Here, we investigated the physiological responses and TaZIPs gene expression in a low (Zhengmai0856, ZM0856) and a high (Aikang58, AK58) grain-Zn-accumulating wheat cultivars under hydroponic conditions with different levels of Zn supply. Results showed that AK58 was a Zn sensitive cultivar with better growth advantage, while ZM0856 was a Zn tolerant cultivar with higher capacity of Zn uptake. In addition, gene expression analysis showed that, the expression levels of the TaZIP3, TaZIP5, and TaZIP7 in roots were increased in both cultivars under Zn deficiency. In shoots, TaZIP3 and TaZIP6 transcript accumulation was lower in AK58 than ZM0856, whereas TaZIP7 showed the opposite effect. Moreover, multivariate statistical analysis (Pearson's correlation and PCA) showed that the mechanisms involved in Zn uptake and translocation was closely related to subcellular biosynthesis and ZIP gene expression regulation, whereas adequate Zn supply improved the Zn uptake and root-to-shoot translocation. These novel findings might be helpful for the molecular-assisted selecting and breeding of Zn-rich wheat cultivars.

Eco-friendly soil amendments improve growth, antioxidant activities, and root colonization in lingrain (Linum Usitatissimum L.) under drought conditions

This study’s primary purpose was to investigate the possible amelioration of limited irrigation conditions by mycorrhiza (AMF), vermicompost, and green manure for lingrain plants. This experiment was accomplished as a factorial based on the completely randomized design with three replications. The first factor was green manure (without green manure and with Trifolium pratense as green manure); the second factor consisted of Rhizophagus irregularis mycorrhiza, vermicompost, a combination of mycorrhiza and vermicompost and none of them, and also the third factor was irrigation regime (full irrigation and late-season water limitation). Green manure, vermicompost, and mycorrhiza single-use enhanced the plant’s underwater limitation conditions compared to the control. However, vermicompost and green manure or mycorrhiza developed a positive synergistic effect on most traits. Combining green manure with the dual fertilizer (mycorrhiza + vermicompost) resulted in the vermicompost and mycorrhiza synergistic effects, especially under limited irrigation. Consequently, the combination of green manure, mycorrhiza, and vermicompost experienced the highest amount of leaf relative water content, root colonization, leaf nitrogen, chlorophyll a, chlorophyll b, carotenoids, antioxidant enzymes activity, grain yield, and oil yield, which would lead to more resistance of plants to limited irrigation conditions.

Effects of Soil pH and Coatings on the Efficacy of Polymer coated ZnO Nanoparticulate fertilizers in Wheat (Triticum aestivum)

This study used ZnO nanoparticles (NPs) as seed treatments and as soil amendments to enhance Zn concentrations in wheat grain. In the seed treatment experiment, seeds were treated with dextran coated (DEX-ZnO) and bare ZnO NP suspensions, in addition to ZnSO₄, at 500 mg Zn/L. In the soil amendment experiment, soil pH was adjusted to 6 and 8, then soils were spiked with 15 mg Zn/kg soil in the form of DEX-ZnO and bare ZnO NPs, as well as ZnSO₄. For the seed treatment, ZnO NPs resulted in significantly higher grain Zn concentration 96.9 ± 25.4 compared to (72.2 ± 25.4), (78.3 ± 24.3), and (81.0 ± 19.4) mg Zn/kg in the control, ZnSO₄, and DEX-ZnO NPs treatments, respectively. In the soil amendment experiment, grain Zn concentrations were the same across all Zn treatments regardless of soil pH. Plants grown at pH 6 had higher Zn accumulation and leaf and stem biomass compared to pH 8. This study demonstrates that treatment of seeds with ZnO NPs can enhance Zn content of grain using far less Zn than is typically used for soil amendments. This may help reduce the environmental impact of Zn fertilization.

Iron oxide nanoparticles ameliorated the cadmium and salinity stresses in wheat plants, facilitating photosynthetic pigments and restricting cadmium uptake

Cadmium and salinity are the major threats to environmental resources and agricultural practice worldwide. The present work aims green synthesis, characterization, and application of iron oxide nanoparticles for co-alleviation of Cd and salt stresses in wheat plants. The iron oxide NPs were synthesized from a native bacterial strain, Pantoea ananatis strain RNT4, yielding a spherical FeO-NPs with a size ranging from 19 to 40 nm evidenced by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images. Results showed that application of 100 mg kg^-1 of the bioengineered FeO-NPs in an original saline soil stimulated wheat plant growth, gaining 36.7% of additional length as compared with the control scenarios, via alleviating the detrimental effects of abiotic stresses and thereby reprogramming the morpho-physiological state of wheat plants. In addition, the presence of FeO-NPs in soil significantly increased the nutrient concentrations of N, P and K⁺, while reducing the Na⁺ and Cl^- components in the wheat grain. Interestingly, application of the FeO-NPs in Cd-polluted soils eventually reduced wheat plant uptake of Cd by 72.5%, probably due to the adsorption of Cd onto the large surface of NPs and thereby, constraining Cd bioavailability to the plants. It provides the first evidence that a FeO-NPs-based treatment could be a candidate agricultural strategy for mitigating the Cd and salt stresses in Cd-polluted saline soils for safe agriculture practice.

Steel mill waste effects on rice growth: comparison of chemical extractants on lead and zinc availability

Zinc deficiency is widespread in cultivated soils, limiting the grain crop production and the adequate human nutrition. Several wastes from metallurgical activity can be used as Zn source, but these materials generally also have other potentially toxic elements, such as Pb, that can be highly toxic for plants and humans. This study aimed to evaluate the efficiency of five chemical extractors (water, citric acid, DTPA, Mehlich 1, and USEPA 3051A) in better correlating with the bioavailable contents of Zn and Pb in soils treated with steel mill wastes (metallurgic press residue (MPR), filter press mud (FPM), and phosphate mud (PM)). Rice plants were cultivated in pots with 4 kg of a Haplic Eutrophic Gleisol and steel mill wastes were applied in soil at increasing doses (0, 0.5, 1, 2, 4, 8, and 16 t ha^-1). The availability of the potentially toxic elements Zn and Pb was assessed as total contents in rice shoots, grains, husks, and roots. The results showed that the USEPA 3051A method extracted greater contents of Zn and Pb from soil compared with other extractants. Due to their greater natural Pb and Zn contents, MPR and PM promoted higher contents of these elements in soils, respectively. Doses of PM influenced Zn contents in grains. After adding 16 t ha^-1 of PM, Zn content in rice grains was 0.1 mg kg^-1. However, at doses 0.5, 1, 2, and 4 t ha^-1, the average concentration of Zn in the grains was 40 mg kg^-1. The wastes MPR and FPM at 16 t ha^-1 promoted Zn concentration in grains of 42 and 45 mg kg^-1, respectively. The greatest contents of Pb in grains were found after addition of FPM at doses 0.5, 1, and 2 t ha^-1: 6.67, 4.96, and 0.45 mg kg^-1, respectively, and above 4 t ha^-1 (4, 8, and 16 t ha^-1); Pb content in grains was less than 0.3 mg kg^-1. The content of Pb in roots at 16 t ha^-1 of PM, MPR, and FPM was 18, 25, and 155 mg kg^-1, respectively, and for Zn, under the same conditions, 100, 255, and 813 mg kg^-1 for MPR, FPM, and PM, respectively. USEPA 3051A can be used to assess Pb and Zn available contents, and positive correlations with bioavailable contents of these elements in roots prove its feasibility. Further studies are necessary to state the safety of using steel mill application, including the use of other crop species, but PM is a promising waste for soil Zn fertilization.

Effects of exogenous sulfur on maize (Zea mays L.) growth and Cd accumulation in Cd-contaminated plastic shed soil

Cadmium (Cd) pollution in plastic shed soils has become increasingly severe, posing a great threat to human health and social stability. Phytoremediation of cadmium pollution is an environmentally friendly and inexpensive remediation method. In this study, maize (Zea mays L.) was selected as the phytoremediation crop by a potted method, and the bioavailability of cadmium was investigated by adding exogenous elemental sulfur. The relationships among the sulfur content, maize growth, cadmium accumulation, and soil parameters were systematically studied. The results showed that, with the supplement of sulfur, the soil pH and activities of soil enzymes (urease, catalase, and sucrase) decreased gradually, and the available heavy metals (Cd, Cr, Zn, and Cu) in soil showed an upward trend. The optimal cadmium enrichment was achieved under T2 by increasing both the biomass of the maize plant and the cadmium concentration in roots and stems. However, T3 and T4 significantly inhibited the growth of maize roots and shoots, leading to a much lower plant biomass compared with that of CK (sulfur-free treatment) and T2. In addition, the cumulative cadmium was not increased because of the low accumulation of cadmium in some parts of the plant. Correlation analyses showed that the sulfur content was negatively correlated with soil pH and maize biomass (P < 0.01), and the cadmium content of whole maize was positively correlated with the dry weight of maize (P < 0.05) and the cadmium content in roots and stems (P < 0.01). In summary, to optimize cadmium phytoremediation of the plastic shed soil, an appropriate concentration of sulfur should be selected in practical applications to ensure that the biomass of the maize is maximized, and the cadmium concentration in different parts of the maize is increased or stabilized.

Increased soil pH and dissolved organic matter after a decade of organic fertilizer application mitigates copper and zinc availability despite contamination

Long-term organic fertilizer (OF) application on agricultural soils is known to induce soil Cu and Zn contamination, along with pH and organic matter changes, which in turn alter the soil Cu and Zn availability. Our study was aimed at assessing Cu and Zn availability in long-term OF-amended soils by distinguishing the importance of increased contamination levels versus pH and organic matter changes in soil. Seventy-four soil samples were collected over time from fields corresponding to three soil types upon which no, mineral, or organic fertilization had been applied over a decade, and thus exhibited a gradient of Cu and Zn contamination, pH, and organic matter concentration. Soil Cu and Zn contamination (i.e. total and DTPA-extractable Cu and Zn concentration), soil solution chemistry (i.e. pH and dissolved organic matter concentration and aromaticity) and Cu and Zn availability (i.e. total concentration and free ionic activity in solution and DGT-available concentration in soil) levels were measured. The Windermere humic aqueous model (WHAM) was used to estimate Zn²⁺ activity and dissolved organic matter (DOM) binding properties in soil solution. Regardless of the soil type, organic fertilization increased Cu and Zn contamination in soil, in addition to the pH and the DOM concentration, aromaticity and binding properties in soil solution. The pH increase prompted a decrease in the total Zn concentration and Zn²⁺ activity in soil solution. The concomitant pH increase and DOM concentration, aromaticity and binding properties boosted the total Cu concentration but decreased the Cu²⁺ activity in soil solution. DGT-available Cu and Zn varied very little between the three fertilization modalities. Our results suggest that pH and DOM changes were able to regulate Cu and Zn availability in long-term OF amended soils by exerting a protective effect that offset the concomitant increase in soil Cu and Zn contamination.

Humic Acid Reduces the Available Cadmium, Copper, Lead, and Zinc in Soil and Their Uptake by Tobacco

Tobacco (Nicotiana tabacum L.) is a crop that is able to accumulate metals. In this study, humic acid was selected as a Cd, Cu, Pb, and Zn passivator, and added to calcareous field soil in amounts of 6.4, 10.3, and 14.8 kg·ha−1. Its impact on the soil fractions of the metals in the soil was extracted by the Community Bureau of Reference (BCR) sequential extraction method, and their accumulation of the metals in tobacco leaves was investigated. Application of 14.8 kg·ha−1 humic acid decreased the DTPA-extracted concentrations of Pb, Cd, Zn, and Cu by 39%, 37%, 29%, and 18%, respectively, as compared with untreated soil. The fractions of Cd, Pb, Cu, and Zn in soil were extracted by the BCR sequential extraction method, and the relationship between the difference metal fractions in the soil and the metal contents in the plant materials were analyzed. The exchangeable fractions of Cd, Pb, Cu, and Zn and the reducible fractions of Pb and Cu are the main bioavailable fractions. Additionally, the reducible fractions of Cd and Zn, the oxidizable fractions of Pb, Cu, and Zn, and all residual fractions of metals were nonbioavailable fractions in the soil. The soils were treated with humic acid (HA) to shift bioavailable metals to stable phases that were less bioavailable. The available Cd, Pb, Cu, and Zn were strongly retained in the soil after the application of humic acid, which decreased the uptake in tobacco in the upper, middle, and lower leaves.

The Effect of Different Organic Fertilizers on Yield and Soil and Crop Nutrient Concentrations

At present, organic fertilizers are not widely used in intensive arable agriculture, and not much is known about their effects on crop nutrition. In a field experiment at Rothamsted, UK, anaerobic digestate (AD), compost, farmyard manure (FYM), straw, and mixes of amendment + straw, were applied at: 1, 1.75, 2.5 or 3.5 t carbon ha−1, with all plots receiving the same input of mineral fertilizer. After five seasons of application, plots receiving non-straw amendments had greater straw and grain yield of 28% and 18% respectively, and plots receiving the highest amendment rate had a 37% higher straw and 23% higher grain yield, compared to control plots. Whereas, the straw-only amendment did not increase yield compared to the control. The concentrations of secondary and micro nutrients in the crop, particularly P, Ca, and S in the straw, and P and Fe in the grain, were significantly greater in the crop receiving non-straw amendment compared to the control. Interestingly K, Fe, and Zn were greater in the crop straw treated with the straw-only amendment. Therefore ‘biomass dilution’ of secondary and micro nutrients did not occur in the higher-yielding amended plots after five seasons, and organic fertilizers would improve the quality of high-yielding, intensively produced crops. The study also demonstrates that portable x-ray fluorescence (pXRF) could be a reliable, cost-effective tool for screening potential organic fertilizers.

Status of cadmium accumulation in agricultural soils across China (1975-2016): From temporal and spatial variations to risk assessment

Based on 1186 published studies, the first national-scale assessment of cadmium (Cd) contamination in agricultural soils across China was conducted. Cd concentrations, temporal and spatial variations, and ecological and health risks resulted from Cd exposure were analyzed. A small part of sampling sites with Cd concentration surpass the screening value and the control value (GB15618-2018), respectively. Soil Cd concentrations in South China were higher than other regions. Ecological risks resulting from Cd contamination were low. Soil Cd concentrations accumulated gradually from 1981 to 2016. Cd mainly came from anthropogenic activities, such as mining, smelting, sewage irrigation, and fertilization. Linear correlations were observed between application amounts of fertilizers and Cd concentrations in soil, indicating that the application of nitrogen, phosphorus, potassium, and compound fertilizers is an important contributor of Cd in soils. This study details the overall Cd contamination status of agricultural soils in China, thus can provide insights for policymakers regarding contamination prevention measures.

Long-term organic matter application reduces cadmium but not zinc concentrations in wheat

Wheat is a staple food crop and a major source of both the essential micronutrient zinc (Zn) and the toxic heavy metal cadmium (Cd) for humans. Since Zn and Cd are chemically similar, increasing Zn concentrations in wheat grains (biofortification), while preventing Cd accumulation, is an agronomic challenge. We used two Swiss agricultural long-term field trials, the "Dynamic-Organic-Conventional System Comparison Trial" (DOK) and the "Zurich Organic Fertilization Experiment" (ZOFE), to investigate the impact of long-term organic, mineral and combined fertilizer inputs on total and phytoavailable concentrations of soil Zn and Cd and their accumulation in winter wheat (Triticum aestivum L.). "Diffusive gradients in thin films" (DGT) and diethylene-triamine-pentaacetic acid (DTPA) extraction were used as proxies for plant available soil metals. Compared to unfertilized controls, long-term organic fertilization with composted manure or green waste compost led to higher soil organic carbon, cation exchange capacity and pH, while DGT-available Zn and Cd concentrations were reduced. The DGT method was a strong predictor of shoot and grain Cd, but not Zn concentrations. Shoot and grain Zn concentrations correlated with DTPA-extractable and total soil Zn concentrations in the ZOFE, but not the DOK trial. Long-term compost fertilization led to lower accumulation of Cd in wheat grains, but did not affect grain Zn. Therefore, Zn/Cd ratios in the grains increased. High Zn and Cd inputs with organic fertilizers and high Cd inputs with phosphate fertilizers led to positive Zn and Cd mass balances when taking into account atmospheric deposition and fertilizer inputs. On the other hand, mineral fertilization led to the depletion of soil Zn due to higher yields and thus higher Zn exports than under organic management. The study supports the use of organic fertilizers for reducing Cd concentrations of wheat grains in the long-term, given that the quality of the fertilizers is guaranteed.

Combined nitrogen fertilizer and wheat straw increases the cadmium phytoextraction efficiency of Tagetes patula

The soil cadmium (Cd) availability and uptake by Tagetes patula grown in two soil types contaminated with Cd and amended with N fertilizer and wheat straw were studied in a pot-culture experiment. The results indicated that N fertilizer treatment (N) and N fertilizer plus straw treatment (NS) promoted T. patula growth, while straw treatment (S) decreased T. patula biomass relative to the control. NS and S treatments increased Cd mobility in the soil and facilitated its uptake by T. patula in Acidic Ferralsols (AF) and Calcaric Cambisols (CC), but the promotion effect was much greater in CC than in AF. The Cd concentrations in the Tagetes shoots in the S and NS treatments were 40% and 27% greater, respectively, than those in the control treatment for AF, and 111% and 80% greater, respectively, for CC. Decreases in soil pH and increases in dissoluble organic carbon concentration after adding N fertilizer and straw were associated with an increase in soil Cd availability and in Cd uptake by T. patula. The results indicate that the NS treatment can alter the soil microenvironment, increasing Cd bioavailability and thus facilitating Cd uptake by T. patula. This work highlights that the combined application of N fertilizer with straw may be a useful way to increase the phytoextraction efficiency of Cd-contaminated soil by the Cd-hyperaccumulator T. patula.

Effects of sulfur application on cadmium bioaccumulation in tobacco and its possible mechanisms of rhizospheric microorganisms

A potting experiment was conducted to investigate the effect of sulfur application on the bioaccumulation by tobacco and its mechanisms of rhizospheric microorganisms. Cadmium content in tobacco was analyzed using atomic absorption spectrometer, while bacterial community and related gene in soil were analyzed via high-throughput sequencing and quantitative PCR techniques, respectively. The obtained results indicated that tobacco had the ability to accumulate cadmium under no sulfur application conditions, with cadmium contents of 35.4, 23.6, and 26.3 mg kg-1 in leaves, stems, and roots, respectively. Under high-sulfur treatment, these values increased to 66.4, 46.1, and 42.6 mg kg-1, respectively, probably due to the increase of the available cadmium content (from 1.1 to 3.3 mg kg-1) in the soil through a decrease of the soil pH value, which was contributed by the sulfur oxidation reaction. dsrA and soxB genes might play an important role in sulfur oxidation, and Thiobacillus sp. was the dominant bacterial genus during the sulfur oxidation process. In addition, sulfur application exerted little effect on the diversity and structure of the soil bacterial community. The combined results indicate that sulfur application is an effective and safe method for Cd phytoextraction by tobacco.

The Use of Q-ICPMS to Apply Enriched Zinc Stable Isotope Source Tracing for Organic Fertilizers

Organic fertilizer applications can contribute to Zinc (Zn) biofortification of crops. An enriched stable isotope source tracing approach is a central tool to further determine the potential of this biofortification measure. Here, we assessed the use of the widely available quadrupole single-collector ICPMS (Q-ICPMS, analytical error = 1% relative standard deviation) and the less accessible but more precise multicollector ICPMS as reference instrument (MC-ICPMS, analytical error = 0.01% relative standard deviation) to measure enriched Zn stable isotope ratios in soil-fertilizer-plant systems. The isotope label was either applied to the fertilizer (direct method) or to the soil available Zn pool that was determined by isotope ratios measurements of the shoots that grew on labeled soils without fertilizer addition (indirect method). The latter approach is used to trace Zn that was added to soils with complex insoluble organic fertilizers that are difficult to label homogeneously. To reduce isobaric interferences during Zn isotope measurements, ion exchange chromatography was used to separate the Zn from the sample matrix. The ⁶⁷Zn:⁶⁶Zn isotope ratios altered from 0.148 at natural abundance to 1.561 in the fertilizer of the direct method and 0.218 to 0.305 in soil available Zn of the indirect method. Analysis of the difference (Bland-Altman) between the two analytical instruments revealed that the variation between ⁶⁷Zn:⁶⁶Zn isotope ratios measured with Q-ICPMS and MC-ICPMS were on average 0.08% [95% confidence interval (CI) = 0.68%]. The fractions of Zn derived from the fertilizer in the plant were on average 0.16% higher (CI = 0.49%) when analyzed with Q- compared to MC-ICPMS. The sample matrix had a larger impact on isotope measurements than the choice of analytical instrument, as non-purified samples resulted on average 5.79% (CI = 9.47%) higher isotope ratios than purified samples. Furthermore, the gain in analytical precision using MC-ICPMS instead of Q-ICPMS was small compared to the experimental precision. Thus, Zn isotope measurements of purified samples measured with Q-ICPMS is a valid method to trace Zn sources in soil-fertilizer-plant systems. For the indirect source tracing approach, we outlined strategies to sufficiently enrich the soil with Zn isotopes without significantly altering the soil available Zn pool.

Effects of long-term fertilization practices on heavy metal cadmium accumulation in the surface soil and rice plants of double-cropping rice system in Southern China

Fertilizer regime is playing an important role in heavy metal cadmium (Cd) accumulation in paddy soils and crop plant. It is necessary to assess the Cd accumulation in soils and rice (Oryza sativa L.) plants under long-term fertilization managements, and the results which help to assess the environmental and food risk in Southern China. However, the effects of different organic manure and chemical fertilizers on Cd accumulation in soils and rice plant remain unclear under intensively cultivated rice conditions. Therefore, the objective was to explore Cd accumulation in paddy soils and rice plant at mature stage under different long-term fertilization managements in the double-cropping rice system. Cd accumulation in the surface soils (0-20 cm) and rice plant with chemical fertilizer alone (MF), rice straw residue and chemical fertilizer (RF), 30% organic matter and 70% chemical fertilizer (LOM), 60% organic matter and 40% chemical fertilizer (HOM), and without fertilizer input (CK) basis on 32 years long-term fertilization experiment were analyzed. The results showed that the soil total Cd content was increased by 0.296 and 0.351 mg kg^-1 and 0.261 and 0.340 mg kg^-1 under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. And the soil available Cd content was increased by 0.073 and 0.137 mg kg^-1 and 0.102 and 0.160 mg kg^-1 under LOM and HOM treatments at early and late rice mature stages, respectively, compared with the CK treatment. The bioconcentration factor of Cd across different parts of rice plant was the highest in root, followed by stem and grain, and the lowest in leaves. At early and late rice mature stages, the root Cd concentration of rice plant was increased by 0.689 and 0.608 mg kg^-1 with HOM treatment, the stem Cd concentration of rice plant was increased by 0.666 and 0.758 mg kg^-1 with RF treatment, and the leaf and grain Cd concentration of rice plant was increased 0.094 and 0.082 mg kg^-1 and 0.086 and 0.083 mg kg^-1 with LOM treatment, respectively, compared with the CK treatment. The soil Cd single-factor contaminant index (P_Cd) under different fertilization treatments was as the following HOM > LOM > RF > MF > CK. Meanwhile, the P_Cd with LOM and HOM treatments was higher than that of the MF, RF, and CK treatments, but there is no significant difference between that of MF and RF treatments. Therefore, long-term application of rice straw residue and chemical fertilizer had no obvious effect on the accumulation of Cd in paddy soils and grain, and soil Cd accumulation was increased as application of organic fertilizer.

Farmyard manure alone and combined with immobilizing amendments reduced cadmium accumulation in wheat and rice grains grown in field irrigated with raw effluents

Cadmium (Cd) stress is a serious concern in agricultural soils worldwide whereas little is known about the impact of farmyard manure (FYM) alone or combined with limestone, lignite and biochar on Cd concentrations in plants. Wheat was grown in Cd-contaminated field amended with control (T₁), FYM @ 0.1% (T₂), FYM + limestone @ 0.05% each (T₃), FYM + lignite @ 0.05% each (T₄), FYM + biochar @ 0.05% each (T₅) and subsequent rice was grown without additional use of amendments. Soil application of amendments increased straw and grain yield and thousand grain weight being maximum in FYM + limestone treatment. Wheat and rice straw yield increased by 19% and 10% in T₃ than control respectively. Photosynthetic pigments increased with the supply of amendments than control. Amendments decreased Cd concentration, total Cd uptake in straw and grains and Cd harvest index of both crops and the maximum reduction in these parameters was recorded with where FYM + limestone (T₃). Cd concentration in wheat and rice straw decreased by 78.5% and 65% in T₃ than control, respectively. The highest benefit to cost ratio was obtained in FYM + limestone (T₃). Ammonium bicarbonate - diethylenetriamine penta acetic acid (AB-DTPA) extractable Cd of the post-harvest soil reduced whereas Cd immobilization index and soil pH increased with the supply of all treatments than control being maximum in T_3. The present study revealed that field management with FYM + limestone increased plant yield and reduced Cd concentrations in grains.

Soil cadmium uptake by cocoa in Honduras

Cadmium (Cd) is a trace metal without essential biological functions that is toxic to plants, animals and humans at low concentrations. It occurs naturally in soils, but inputs from anthropogenic sources have increased soil Cd contents worldwide. Cadmium uptake by cocoa (Theobroma cacao L.) has recently attracted attention, after the European Union (EU) decided to bring into force values for maximum Cd concentrations in cocoa products that would be exceeded by current products of various provenances from Latin America. In order to identify factors governing Cd uptake by cocoa, we carried out a survey on 55 cocoa farms in Honduras in which we determined Cd concentrations in cocoa leaves, pod husks and beans and analysed their relationships to a variety of surrounding soil and site factors. Averaging 2.6±0.4mgkg^-1, the concentrations of Cd were higher in the leaves than in the beans. With an average of 1.1±0.2mgkg^-1, the bean Cd concentrations still exceeded the proposed EU limit, however. The bean Cd showed large differences between geological substrates, even though regional variations in 'total' soil Cd were comparably small and the average concentration was in the range of uncontaminated soils (0.25±0.02mgkg^-1). As we found no influence of fertilizer application or vicinity to industrial sites, we conclude that the differences in soil Cd between sites were due to natural variation. Of all factors included here, DGT-available soil Cd was the best predictor of bean Cd (R²=0.5). When DGT was not considered, bean Cd was best predicted by 'total' soil Cd, pH and geology. The highest bean Cd concentrations were found on alluvial substrates.

Fungal Diversity in Tomato Rhizosphere Soil under Conventional and Desert Farming Systems

This study examined fungal diversity and composition in conventional (CM) and desert farming (DE) systems in Oman. Fungal diversity in the rhizosphere of tomato was assessed using 454-pyrosequencing and culture-based techniques. Both techniques produced variable results in terms of fungal diversity, with 25% of the fungal classes shared between the two techniques. In addition, pyrosequencing recovered more taxa compared to direct plating. These findings could be attributed to the ability of pyrosequencing to recover taxa that cannot grow or are slow growing on culture media. Both techniques showed that fungal diversity in the conventional farm was comparable to that in the desert farm. However, the composition of fungal classes and taxa in the two farming systems were different. Pyrosequencing revealed that Microsporidetes and Dothideomycetes are the two most common fungal classes in CM and DE, respectively. However, the culture-based technique revealed that Eurotiomycetes was the most abundant class in both farming systems and some classes, such as Microsporidetes, were not detected by the culture-based technique. Although some plant pathogens (e.g., Pythium or Fusarium) were detected in the rhizosphere of tomato, the majority of fungal species in the rhizosphere of tomato were saprophytes. Our study shows that the cultivation system may have an impact on fungal diversity. The factors which affected fungal diversity in both farms are discussed.