Soil pollution by heavy metals affects soil quality worldwide. Cadmium (Cd) is of special concern because it might transfer from soil to plants, especially under acidic conditions, causing toxicity. This work aimed to evaluate the LC50 (lethal concentration to 50% of studied population), NOEC (no observed effects concentration) and LOEC (lowest observed effects concentration), by measuring the germination and growth of eight plant species (Beta vulgaris, Daucus carota, Lactuca sativa, Phaseolus vulgaris; Avena strigosa, Oryza sativa, Triticum aestivum and Zea mays) in soil under increasing Cd concentrations (0, 10, 40, 80, 160, and 320 mg kg-1) and two levels of acidity. Increasing the soil pH (from 4.1 to 6.4) by liming alleviated Cd toxicity and had a positive impact on seedling growth of all plant species studied. Germination was a less responsive endpoint and only the most sensitive species (L. sativa, B. and D. carota) were affected under the most acidic condition. These results were confirmed by the lower values found for LOEC and LC50 in these species regardless of the soil pH. Sensitive species are thus recommended as indicators of soil contamination in ecotoxicological studies, in which dicotyledonous species (e. g. L. sativa and B. vulgaris) are more suitable for risk assessments in Cd-contaminated soils at low concentrations, whilst monocotyledons (e. g. Z. mays) are more adequate for higher Cd concentrations (≥ 80 mg kg-1). Increasing soil pH by liming was demonstrated to be an efficient method in alleviating Cd toxicity in seedling growth.

Accumulation of heavy metals in unconsolidated soils can prove toxic to proximal environments, if measures are not taken to stabilize soils. One way to minimize the toxicity of metals in soils is the use of materials capable of immobilizing these contaminants by sorption. Biochar (BC) can retain large amounts of heavy metals due to, among other characteristics, its large surface area. In the current experiment, sugarcane-straw-derived biochar, produced at 700 °C, was applied to a heavy-metal-contaminated mine soil at 1.5, 3.0, and 5.0% (w/w). Jack bean and Mucuna aterrima were grown in pots containing a mine contaminated soil and soil mixed with BC. Pore water was sampled to assess the effects of biochar on zinc solubility, while soils were analyzed by DTPA extraction to confirm available metal concentrations. The application of BC decreased the available concentrations of Cd, Pb, and Zn in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water. Amendment with BC reduced plant uptake of Cd, Pb, and Zn with the jack bean uptaking higher amounts of Cd and Pb than M. aterrima. This study indicates that biochar application during mine soil remediation could reduce plant concentrations of heavy metals. Coupled with this, symptoms of heavy metal toxicity were absent only in plants growing in pots amended with biochar. The reduction in metal bioavailability and other modifications to the substrate induced by the application of biochar may be beneficial to the establishment of a green cover on top of mine soil to aid remediation and reduce risks.

Heavy metals in soil are naturally occurring but may be enhanced by anthropogenic activities such as mining. Bio-accumulation of heavy metals in the food chain, following their uptake to plants can increase the ecotoxicological risks associated with remediation of contaminated soils using plants. In the current experiment sugar cane straw-derived biochar (BC), produced at 700 °C, was applied to a heavy metal contaminated mine soil at 1.5%, 3.0% and 5.0% (w/w). Jack bean (Canavalia ensiformis) and Mucuna aterrima were grown in pots containing soil and biochar mixtures, and control pots without biochar. Pore water was sampled from each pot to confirm the effects of biochar on metal solubility, whilst soils were analyzed by DTPA extraction to confirm available metal concentrations. Leaves were sampled for SEM analysis to detect possible morphological and anatomical changes. The application of BC decreased the available concentrations of Cd, Pb and Zn in 56, 50 and 54% respectively, in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water (1st collect: 99 to 39 μg L(-1), 2nd: 97 to 57 μg L(-1) and 3rd: 71 to 12 μg L(-1)). The application of BC reduced the uptake of Cd, Pb and Zn by plants with the jack bean translocating high proportions of metals (especially Cd) to shoots. Metals were also taken up by Mucuna aterrima but translocation to shoot was more limited than for jack bean. There were no differences in the internal structures of leaves observed by scanning electron microscopy. This study indicates that biochar application during mine soil remediation reduce plant concentrations of potential toxic metals.

Selenium is an essential trace element required in low amounts by humans and animals, but it can be toxic when ingested at high concentrations. Information regarding Se background levels in soils is important to prevent Se deficiency, to optimize human nutrition, and to prevent toxicological effects. Background Se levels in Brazilian soils were evaluated and correlated with other soil characteristics. Se concentrations were quantified in samples from the superficial layer (0–0.2 m) and from the subsurface layer (the highest portion of the B horizon) for 58 soils. Soils were selected across a wide range of soil types and parent materials. Se concentrations ranged from <0.08 to 1.61 mg kg−1, with a mean of 0.19 mg kg−1. Concentrations of Se in the samples collected in the superficial layer were positively correlated with cation exchange capacity, as well as with clay, organic matter, and oxide contents of the soils. In the subsurface samples, only pH and aluminum oxide content were correlated with Se concentrations.

Objetivou-se, com este trabalho, avaliar a torta de filtro e a turfa como fontes de matéria orgânica (MO) para mitigar solo contaminado com boro, sob o cultivo do girassol. O delineamento experimental adotado foi inteiramente casualizado e os tratamentos foram distribuídos em esquema fatorial 2 (materiais orgânicos) x 4 (doses de cada fonte de matéria orgânica), com três repetições. As doses de cada material orgânico adicionado se fundamentaram nos teores de C, sendo equivalentes a 0, 20, 40 e 80 t ha-1. Em cada parcela experimental foram utilizados vasos contendo 5,0 kg de solo contaminado cultivados com três plantas de girassol, durante 65 dias. As plantas não apresentaram sintomas de toxicidade por B, Cu e Zn, embora seus teores na parte aérea tenham sido elevados. O tipo de matéria orgânica influenciou significativamente a produção de massa seca do caule, flor e raiz, sendo que a adição de torta de filtro promoveu maior produção. O tempo de remoção necessário para retirar 50% do teor total de B do solo seria de 11,1 anos sem uso de MO, 15 anos com uso da torta de filtro e 25 anos com uso da turfa. O girassol tem potencial para ser cultivado na área contaminada com resíduo metálico e a aplicação de torta de filtro ou de turfa não foi eficiente como mitigadora de metais pesados e de B.The objective of this study was to evaluate the filter cake and peat as sources of organic matter (OM) in order to mitigate contaminated soil with boron, under the sunflower cultivation. The experimental design adopted was completely randomized in a factorial scheme distributed in 2 (organic matter types) x 4 (organic matter dose of each type), with three replications. The doses of each organic material added were based on the content of C, being equivalent to 0, 20, 40 and 80 t ha-1. In each experimental plot, pots containing 5.0 kg of contaminated soil was cultivated with three plants of sunflower during 65 days. The plants showed no symptoms of toxicity of B, Cu and Zn, although high levels were observed in the aerial part. The type of organic matter significantly influenced the dry mass of stem, flower and root, though the addition of filter cake promoted higher production. The time required to remove 50% of the total content of B in soil was 11.1 years without the use of OM, 15 years with the use of filter cake and 25 years with the use of peat. The sunflower has the potential to be grown in the contaminated area and the application of filter cake or peat was not as efficient in mitigation of heavy metals and B.

The objective of this study was to evaluate the filter cake and peat as sources of organic matter (OM) in order to mitigate contaminated soil with boron, under the sunflower cultivation. The experimental design adopted was completely randomized in a factorial scheme distributed in 2 (organic matter types) x 4 (organic matter dose of each type), with three replications. The doses of each organic material added were based on the content of C, being equivalent to 0, 20, 40 and 80 t ha(-1). In each experimental plot, pots containing 5.0 kg of contaminated soil was cultivated with three plants of sunflower during 65 days. The plants showed no symptoms of toxicity of B, Cu and Zn, although high levels were observed in the aerial part. The type of organic matter significantly influenced the dry mass of stem, flower and root, though the addition of filter cake promoted higher production. The time required to remove 50% of the total content of B in soil was 11.1 years without the use of OM, 15 years with the use of filter cake and 25 years with the use of peat. The sunflower has the potential to be grown in the contaminated area and the application of filter cake or peat was not as efficient in mitigation of heavy metals and B.

In Brazil, the production of potted plants in substrates under semi- or protected cultivation is an economically important activity. The substrate nutrient management in potted plant production is not easy, due to non-standardized methods of water extraction for chemical analysis of nutrients that may lead to misinterpretation of nutrient results. The objective of this research was to evaluate current water extraction methods for the chemical analysis of a coir substrate incubated with conventional-NPK and slow-release fertilizers (SRF). Substrate samples were collected at 20, 60 and 120 days after incubation, for the determination of micronutrients using water extraction: 1:1.5; 1:2; 1:5; 1:10; and saturated extract (SE). Cl, B, Cu and Fe concentrations in extracts were not affected by the incubation period, however, Zn and Mn concentrations increased with time. The SE and 1:1.5 extraction methods were the most effective in discriminating differences among fertilization treatments. They resulted in higher values for Cl, Fe, Mn and Zn, than any of the water extracts. They were good for the evaluation of Cu concentration in fertilized coir substrate.

Substrates for plants are of varied composition and the non-standardized water extraction methods for nutrient chemical analysis have raised difficulties to adequately interpret results and manage substrate fertilization and/or correction. In the United States (USA), the saturation extract procedure is widely adopted, while in Europe, the water extraction using fixed volumes (1:1.5 v/v; 1:2 v/v; 1:5 v/v; 1:10 m/v) is used. This research aimed at evaluating the current water extraction methods for the chemical analysis of peat incubated with conventional (NPK) and slow-release fertilizers (SRF). The treatments were applied as follows: (1) control; (2) lime; (3) lime + NPK + S; (4) lime + NPK + S + micronutrients; (5) lime + slow-release fertilizer (SRF) + S and; (6) lime + SRF + S + micronutrients. Both, NPK and SRF (formula N P2O5 - K2O = 14-14-14) were applied at a rate of 6 g L-1 of substrate. Substrate samples were collected at 20, 60 and 120 days after incubation for the determination of micronutrient concentrations, using the following water extraction methods: 1:1.5 v/v; 1:2 v/v; 1:5 v/v; 1:10 m/v; and saturation extract. The micronutrient concentrations were influenced by fertilization treatments (NPK or SRE with micronutrients), especially B. No effect was observed on Cu, Fe and Zn concentrations. Manganese was the most affected by liming, since significant decrease on Mn concentration was observed with the pH increase. The incubation period had little influence on B and Fe concentrations, but affected Cu, Mn and Zn, which concentrations tended to increase with time. Such effect was more evident in the SRF treatments. On the overall, positive and high correlations were found between the several extraction procedures (correlation coefficients > 0.92) for B, Mn and Zn data. There was no correlation between methods for Cu and Fe. The saturation extract best discriminated the fertilization treatments, followed by the 1:1.5 extract.

This research was aimed at evaluating the current water extraction methods for the analysis of four substrates treated with and without micronutrients. Black peat, coir, rice hulls, and pine bark ( Pinus elliotis) were treated as follows: 1) control, 2) nitrogen, phosphorus, and potassium (NPK), and 3) NPK + M (micronutrients). Substrate samples were collected at 20 and 120 days of incubation for the determination of micronutrient concentrations. After 120 days of incubation, B, Mn, and Zn were easily detected in the SE, 1:1.5 v/ v, and 1:2 v/ v extracts from treatments with added micronutrients. Cu and Fe concentrations did not differ among treatments, irrespective of the extraction method used. Pine bark and black peat showed the lowest micronutrient concentrations for B and Zn; coir showed high values for B, Fe, and Zn concentrations; and rice hulls showed the highest Mn and Zn concentrations. SE and the 1:1.5 water extract were the best methods for substrate micronutrients evaluation.

Substrates for plants may present varied composition, from a single component to a complex mixture of different materials, which may present low, adequate or high plant nutrient concentrations. Some substrates, depending on the origin, may present high heavy metal concentrations. The determination of total element concentrations for the chemical characterization of these materials turns an important issue not only for fertilizer recommendation but also for quality control. The objective of this research was to evaluate the total concentrations of some elements in Brazilian commercial substrates using two heating processes, as well as to investigate the levels of heavy metals, which are related to the quality of the material. Nine organic substrates and one inorganic, commercialized in Brazil, were used for the determination of total- P, K, Ca, Mg, S, Na, Cu, Fe, Mill, Zn, Cd, Cr, Ni and Ph concentrations, using two digestion procedures (open system acid digestion and microwave-oven digestion. For P, K, Ca, Mg, Na, Mn, Zn and Cr the total element concentrations were very similar irrespective of the technique used, with angular coefficients close to 1.0. On the other hand, for S, Cu, Fe and Cd there was a variation above 20% in the total element concentrations. The nitric-perchloric digestion extracted around 26% more Cu when compared with nitric- microwave method. An opposite tendency was observed for the elements S and Fe, since the nitric-microwave procedure presented 21 to 29 % larger extraction, respectively. Total heavy metals determination is recommended for monitoring the composition of substrates used in agriculture.

A avaliação do método modificado da resina de troca de íons para extração de Mn e Fe dos solos foi o objetivo desta pesquisa. Foram utilizadas 44 amostras de solo, cujos teores de Mn variaram de baixos a altos e de Fe de médios a altos. Como plantas-teste, utilizaram-se o milho e a soja, cultivadas em casa de vegetação. O Fe e o Mn do solo foram determinados, usando o método modificado da resina de troca de íons, DTPA, AB-DTPA, Mehlich-1 e Mehlich-3. Os coeficientes de correlação entre Mn no solo e Mn acumulado na parte aérea da soja foram: resina (0,62*), DTPA (0,58*), Mehlich-3 (0,54*), Mehlich-1 (0,51*) e AB-DTPA (0,26NS). Para o milho, houve correlação entre Mn-solo e Mn-planta somente nas amostras de solo com baixos teores desse elemento, para todos os extratores, exceto para AB-DTPA. Concluiu-se que a resina foi tão eficiente quanto os extratores DTPA, M-1 e M-3 em avaliar a disponibilidade de Mn para a soja, e que nenhum extrator foi eficiente em avaliar a disponibilidade de Fe para as plantas de milho e soja, com 53 dias de idade, cultivadas em casa de vegetação.The objective of this research was to evaluate a modified ion exchange resin method for Mn and Fe extraction from soils. Forty-four soil samples presenting low, medium, and high Mn and medium to high Fe concentrations were used. Maize and soybeans plants were grown as test plants in a pot experiment in a greenhouse. Soil samples were analyzed for Mn and Fe using the modified ion exchange resin, DTPA, AB-DTPA, Mehlich-1, and Mehlich-3 methods. The correlation coefficients between soil Mn and Mn accumulated in the soybean shoot were: ion exchange resin (0.62*), DTPA (0.57*), Mehlich-3 (0.54*), Mehlich-1 (0.51*), and AB-DTPA (0.26). For maize, significant correlation coefficients between soil Mn and plant-Mn were obtained only when low-initial Mn soil samples were considered for all extractants, except for AB-DTPA. For soybeans, the modified ion exchange resin method was as efficient as DTPA, Mehlich-1 and Mehlich-3 for the evaluation of soil Mn availability. None of the methods was efficient for evaluating the soil Fe availability for the 53 day-old maize and soybean plants grown in greenhouse.

The influence of the arbuscular mycorrhizal fungus (AMF) Glomus macrocarpum Tul. and Tul. on Bradyrhizobium-inoculated soybean (Glycine max L. Merrill var. IAC-14) growth, nutrients and Pb uptake was studied in soils with different levels of Pb. Mycorrhizal and non-mycorrhizal plants were grown in a soil amended with 0, 150, 300 and 600mgdm−3 of Pb, using Pb(NO3)2, and plants were harvested at two different growth stages: flowering and maturity. Soybean shoot dry weights were not affected by increasing doses of lead in the soil, but the number of pods decreased significantly. Nodule dry weights of mycorrhizal roots were reduced by soil Pb additions, although the mycorrhizae stimulated plant nodulation significantly. The inoculation of AMF in soybeans provided higher rates of nutrients uptake, mainly P, inducing greater mycorrhizal-soybean growth. Thus, mycorrhizae improved Pb uptake, produced shoots with Pb concentrations 30% lower than those of non-mycorrhizal plants, at the highest Pb concentration added to the soil. AM fungus was more susceptible to the higher Pb doses added to the soil than the soybean plants, decreasing both root AM colonisation and spore production. This work indicated that a concentration of 600mgdm−3 of Pb in the soil interfered with the establishment of double symbioses between AMF and Bradyrizhobium, and with the fungus perpetuation in the soil.

The objective of this research was to evaluate a modified ion exchange resin method for Mn and Fe extraction from soils. Forty-four soil samples presenting low, medium, and high Mn and medium to high Fe concentrations were used. Maize and soybeans plants were grown as test plants in a pot experiment in a greenhouse. Soil samples were analyzed for Mn and Fe using the modified ion exchange resin, DTPA AB-DTPA Mehlich-1, and Mehlich-3 methods. The correlation coefficients between soil Mn and Mn accumulated in the soybean shoot were: ion exchange resin (0.62*), DTPA (0.57*), Mehlich-3 (0.54*), Mehlich-1 (0.51*), and AB-DTPA (0.26). For maize, significant correlation coefficients between soil Mn and plant-Mn were obtained only when low-initial Mn soil samples were considered for all extractants, except for AB-DTPA. For soybeans, the modified ion exchange resin method was as efficient as DTPA, Mehlich-1 and Mehlich-3 for the evaluation of soil Mn availability. None of the methods was efficient for evaluating the soil Fe availability for the 53 day-old maize and soybean plants grown in greenhouse.

Existem divergências sobre o efeito do fungo micorrízico arbuscular (FMA) na absorção de metais pesados pelas plantas. Isso pode ser atribuído não só às diferenças na disponibilidade do metal no solo, espécie de FMA e de planta, mas também às possíveis interações que ocorrem entre estes e os demais fatores ambientais. Realizou-se um experimento em casa de vegetação, com a finalidade de avaliar o efeito da inoculação de FMAe da saturação por bases do solo sobre o crescimento, nutrição e absorção de Pb em soja crescida em um Latossolo Vermelho-Amarelo. Os tratamentos consistiram de inoculação, ou não, de Glomus macrocarpum, duas doses de calcário, elevando a saturação por bases do solo a 63 e 82 %, e cinco doses de Pb (0; 7,5; 37,5; 150 e 300 mg dm-3), utilizando-se como fonte Pb(NO3)2. A inoculação do FMA aumentou a produção de matéria seca da parte aérea das plantas, as quais também apresentaram maiores teores de P e maiores quantidades acumuladas de P, Ca, Mg, Mn, Fe e Zn. A produção de matéria seca da soja micorrizada reduziu linearmente com o aumento da dose de Pb adicionada, em ambas as saturações por bases. No solo com menor V %, a colonização radicular pelo FMA diminuiu 40 % na maior dose de Pb adicionada, o teor de Pb na parte aérea da soja foi cinco vezes maior e as plantas micorrizadas apresentaram um teor de Pb 30 % menor do que as não micorrizadas. A adição de Pb afetou tanto o estabelecimento quanto o desempenho da simbiose. O FMA teve papel relevante na diminuição da concentração do Pb na parte aérea da soja, no solo com menor saturação por bases, conferindo tolerância à planta em uma condição de excesso de metal pesado no solo.

The increasing use of the ICP-AES (inductively coupled plasma atomic emission spectrophotometry) as a multielement Analytical technique has stressed the preference for the use of multinutrient extractants in routine soil analysis. However, few studies relating the extraction of zinc (Zn) from soil with such extractants and the absorption of the element by plants have been published. Two experiments under greenhouse conditions were carried out in order to determine the efficiency of some multinutrient extractants for the determination of available Zn in 44 soils from the State of Sao Paulo, Brazil, for corn and soybean. All soil samples were limed to increase the CEC's base saturation at pH 7 to 70%. Twenty-two soil samples with DTPA (diethylenetriaminepentaacetic acid) extractable Zn concentration lower than 0.6 mg dm(-3) received either the application of B, Cu, Mn, Zn or of these micronutrients excluding Zn. The remaining 22 soil samples, with Zn concentration above 0.6 mg dm(-3), received application of three micronutrients (B, Cu and Mn). Macronutrients were applied to all pots as needed for crop development. Zinc was extracted from the soils before each planting using the extracting solutions, DTPA, Mehlich 1 (M-1), Mehlich 3 (M-3) and AB-DTPA (ammonium bicarbonate-DTPA) and determined by ICP-AES. The results showed significant correlations between plant Zn concentration and soil Zn concentration. The correlation values between soil-Zn and plant-Zn were of 0.74 (M-3), 0.73 (DTPA), 0.62 (AB-DTPA) and 0.61 (M-1) for corn, and of 0.71 (DTPA), 0.63 (M-1), 0.58 (M-3) and 0.46 (AB-DTPA) for soybean. Thus, the DTPA solution was the most efficient extractant for the determination of bioavailable Zn when both crops are considered together.