Transport of Polycyclic Aromatic Hydrocarbons in a Calcareous Wetland Soil

Knowledge of transport and degradation of polycyclic aromatic hydrocarbons (PAHs) is important in assessing PAH contamination of soils and water resources. The transport of naphthalene, anthracene, pyrene and phenanthrene was determined in a contaminated calcareous soil obtained from the Shadegan wetland (Khozestan, Iran) considering a column study in laboratory conditions. The PAHs were added to the top 5 cm of soils at 75 and 150 mg kg-1 and leachates were collected for 10 pore volumes. PAH concentrations in the leachate fractions and soils (0-5, 5-10, 10-15 and 15-20 cm depths) were determined using high pressure liquid chromatography. Results showed that naphthalene had the most mobility among the PAHs, and differences among the mobility of selected PAHs were related to their water solubility and structure. Mass balance demonstrated that among the selected PAHs, anthracene and naphthalene were the most and the least recalcitrant compounds, respectively. Hence, naphthalene could have the greatest potential to contaminate surface and ground waters which should be considered apparently

Uptake and root-to-shoot transfer of cadmium in alfalfa from a soil treated with sewage sludge, municipal waste compost and cow manure

Background: Cadmium ( Cd) is one of the most toxic heavy metals and is considered non-essential for living organisms . This metal is easily absorbed by plants and transported to the animal and human food chain. Organic residuals used as fertilizers or amendments in agricultural lands are the main sources of Cd in soil. It is important to study uptake and translocation of Cd by plants grown in Cd-contaminated soils. The purpose of this greenhouse study was to investigate the impact of sewage sludge, municipal waste compost and cow manure on uptake and root to shoot translocation of Cd in alfalfa. Materials and Methods: A completely randomized design with three treatments (sewage sludge, compost and cow manure applied at 25 Mg/ha) and three replicates was used. Alfalfa seedlings were harvested 60 days after planting and the uptake and translocation of Cd were measured in their shoot. Results: Results indicated that the greatest Cd uptake by alfalfa shoot was obtained in the compost treatment. The percentage of Cd translocated to the shoots of alfalfa in compost treatment was greater compared to the other treatments. Application of cow manure significantly decreased uptake and translocation of Cd. Conclusion: The results of this study reveal that the Cd source and plant species are important factors in evaluation of uptake and translocation of Cd to the edible parts of plants

The Effect of Preceding Crops on the Chemical Fractions of Copper (Cu) in the Rhizosphere and the Bulk Soil and its Relationship with Copper Uptake by Wheat

Introduction: Preceding crops as a source of organic matter are an important source of micronutrient and can play an important role in the soil fertility and the micronutrients cycle of soil. In addition to the role of the organic matter in increasing the concentration of micronutrients in soil solution, attention also should be paid to the role of the kind and the quantity of the root’s exudates that are released in response to the incorporation of different plant residues in the rhizosphere. Present research was conducted with the objective of studying the effect of the kind of preceding crops: Trifolium (Trifolium pretense L), Sofflower (Carthamus tinectirus L), Sorghum (Sorghum bicolor L), Sunflower (Heliantus annus L) and control (fallow) on the chemical forms of copper in the wheat rhizosphere and the bulk soil and Cu uptake by wheat and also investigating the correlation between the fractions of Cu in soil and Cu uptake in wheat. Materials and Methods: The present research was conducted as split plot in a Randomized Complete Block design (RCBD) with 3 replications and 5 treatments, in field conditions. In the beginning, the preceding crops were cultivated in the experimental plots and after ending growth, preceding crops were harvested. Then the wheat was cultivated in the experimental plots. Finally, after harvesting the wheat, soil samples were collected from the two parts of the root zone (the wheat rhizosphere and the bulk soil). The soil samples were air dried ground and passed through a 2-mm sieve and stored for chemical analysis. Soil pH (in the soil saturation extract) and organic matter (Walkley–Black wet digestion) were measured in standard methods (1). The Total Organic Carbon (TOC) was measured by Analyzer (Primacs SLC TOC Analyzer (CS22), Netherlands). The available Cu in soil was extracted by DTPA and determined using atomic absorption spectroscopy (2). The fractionation of soil Cu was carried out using the MSEP method (3). Results and Discussion: The results showed that the preceding crops significantly decreased soil pH, also significantly increased the DOC and DTPA-extractable Cu.These changes were higher in the Trifolium preceding treatment in the rhizosphere soil. Also, the preceding crops significantly decreased Carbonate -Cuand Residual-Cu fractions in the wheat rhizosphere compared with the bulk soil. The preceding crops (except Trifolium) significantly increased Oxide-Cu fraction. The soil Oxide- Cu fraction was higher in the rhizosphere in comparison with the bulk soil. The preceding crops increased the Organic-Cu in both the wheat rhizosphere and the bulk soil and it was higher in Trifolium treatment. The preceding crops increased Cu uptake by wheat and Organic-Cu positively correlated with Cu uptake by wheat. Conclusion: The Organic-Cu fraction increased in the rhizosphere compared with the bulk soil, whereas Oxide- Cu, Carbonate–Cu and Residual-Cu fractions decreased. According to the results, the observed increase in the copper concentration of organic fraction in the rhizosphere was due to the decrease in the copper concentration of carbonate, oxide and residual fractions. In fact, the main process is the transmission of copper from carbonate, oxide and residual fractions to another fraction. Also, the results showed that the root exudates of the preceding crops and wheat affected the different forms of copper in the soil solid phase. Furthermore, the results of copper forms correlation analysis with Cu uptake by wheat showed that the Organic-Cu fraction had more important role in supplying copper was needed for wheat. Therefore, the preceding crops increased the copper concentration of organic fraction in the rhizosphere compared with the bulk soil, and these changes are associated with increasing the amount of copper uptake in wheat

Variação do potencial total da água em uma toposseqüência de solos de tabuleiro, durante dois anos Total water potential variation in a soil table land topsequence, during two years

O trabalho teve como objetivo avaliar quinzenalmente, em 1996 e 1997, a variação do potencial total da água ao longo do tempo, em solos de uma toposseqüência de tabuleiro localizada em Sapeaçu, BA. Esta toposseqüência tinha as seguintes características: a) comprimento de 190 m; b) declividade média de 0,097 m m-1; c) cultivo com laranja; d) Latossolo Amarelo argissólico coeso, no terço superior; e) Argissolo Amarelo coeso, no terço médio; f) Argissolo Acinzentado não coeso, no terço inferior. A umidade do solo foi medida com sonda de nêutrons, nas profundidades de 0,30, 0,70, 1,10 e 1,50 m. Com base nas respectivas curvas de retenção, obteve-se o potencial matricial e, em seguida, o potencial total da água, para cada solo, profundidade e tempo. A camada coesa dificulta o fluxo de água no solo, tanto no processo de molhamento como no de secamento. Em conseqüência, o potencial total da água em solos com camada coesa varia bruscamente na camada mais superficial, ao longo do tempo, e mais lentamente nas camadas mais profundas. Em solo não coeso, a variação brusca do potencial ocorre apenas na camada mais superficial. O limite de tensão de água no solo de -1.500 kPa como sendo o ponto de murchamento permanente não se aplica à cultura dos citros.<br>The objective of this work was to evaluate, fortnightly, during 1996/1997, the total soil water potential variation in a tableland topsequence in Sapeaçu county, BA, Brazil. This topsequence had the following characteristics: a) length of 190 m; b) slope of 0.097 m m-1; c) orange as growing crop; d) the upper third with a cohesive argisolic Yellow Latosol; e) the middle third with a cohesive Yellow Argisol; and f) the lower third with a non-cohesive Gray Argisol. Soil water was estimated by neutron probe at depths of0.30, 0.70, 1.10, and 1.50 m. Based on water retention curves, matric potential and, in sequence, total soil water potential were determined, for each soil and depth in different times. The cohesive layer makes difficult the water flow in the soil profile, both in the wetting and in the drying processes. Consequently, the total water potential in soils with cohesive layer changed abruptly in the most superficial layer, during the time, and slowing in the deepest layers. In non-cohesive soil, the water potential changed abruptly only in the most superficial layer. The -1,500 kPa limit of soil water pressure as permanent wilting point is not applied to orange crop