Antonio Paz-González

Pb-phytoextraction by maize in a Pb-EDTA treated Oxisol

One of the most viable strategies to restore metal contaminated soils is the introduction of plants specialized in their accumulation or able to tolerate very high metal concentrations. This research evaluated: i. the maize as a Pb-accumulator plant; ii. the effects of EDTA-chelating agent for Pb-uptake by maize; iii. amending effect of EDTA on the soil Pb-availability using different extracts. Treatments consisted of Pb rates (100; 200; 350; 1,200 and 2,400 mg kg -1 ) applied to a Rhodic Hapludox in the form of Pb 3 (NO) 2 with (0.5 g kg -1 ) and without EDTA. Lead concentrations were determined in maize plant shoots. Soil available Pb was obtained using DTPA, Mehlich-3 and saturation solutions methods. Ionic speciation in the soil solution was performed using the software Visual-Minteq. Although a low t value was found (t 1,500 mg kg -1 of Pb) in maize shoots regardless of EDTA addition. Maize plants treated with EDTA had lower dry matter yield, mainly due to toxic levels of Fe and Al of the Oxisol. All extracting solutions were effective to determine available Pb in soil samples, but the saturation extract is a more difficult and time consuming procedure. At low and medium Pb levels, the plants grew less on EDTA, therefore the phytoextration process was less efficient. The addition of EDTA to the soil is not recommended with the purpose of increasing Pb

Trace Elements Extracted by DTPA and Mehlich‐3 from Agricultural Soils with and without Compost Additions

Abstract Risks of soil contamination when waste materials are used as fertilizers have been a matter of frequent concern. The effect of compost from municipal organic waste on trace element status was examined in short‐term field trials at neighboring areas of A Coruña (northwest Spain). The study sites were characterized as medium textured soils, with a range of pHs, organic matter content, and cation exchange capacity. The objective of this work was to compare two extraction methods (DTPA and Mehlich‐3) to determine micronutrient contents in soils with and without compost additions. DTPA and Mehlich‐3 extractions were carried out, and then analyses for Fe, Mn, Cu, Zn, Ni, Cr, Pb, and Cd contents were performed by ICP‐AES. Overall, DTPA was less efficient than Mehlich‐3 for Fe and Mn extraction. Lead, Ni, and Cd were extracted more effectively by DTPA than by Mehlich‐3. In general, the efficiency of the extractants was related to compost addition, a trend that was most apparent for Zn and Cu. Levels of trace metals extracted by DTPA and Mehlich‐3 from soils without compost addition were already highly variable, because of traditional farmyard manure and slurry fertilization. Diagnostic criteria for allowable loading limits of heavy metals during compost application should take into account direct measurements of background levels and relevant soil properties such as soil acidity.

DTPA AND MEHLICH-3 MICRONUTRIENT EXTRACTABILITY IN NATURAL SOILS

Most soils of the humid area in the Iberian Peninsula are characterized by acid, desaturated, organic rich surface horizons. In this study micronutrients (Cu, Fe, Mn and Zn) were extracted using DTPA and Mehlich-3. Total contents were also determined by digestion with nitric acid. Seven natural soil profiles, representing major acid soil types developed over a wide variety of parent materials were collected. In addition, three soil profiles containing carbonates and/or a high base saturation were sampled. The organic matter content when all samples were included in the data set ranged between 0.37 and 26.51%. For the acid set of samples, Mehlich-3 extractable concentrations of Cu, Fe, Mn and Zn were higher than contents extracted by DTPA. However, DTPA extracted higher concentrations of Cu, Fe and Mn than Mehlich-3 in near neutral or calcareous soils. Correlation coefficients between DTPA and Mehlich-3 extractable amounts were in the range from 0.49 to 0.96 for the set of acid soil samples and in the range from 0.71 to 0.92 for non-acid horizons. However, for acid and non-acid samples combined, correlations between micronutrient contents extracted by both solutions were much weaker and not significant. Results illustrate difficulties for selecting a single multielement extractant for different soils of the studied region. Interactions between micronutrient extractability, pH and organic matter content were evaluated. In all of the studied soil profiles, there was a decrease in the extractable Cu, Fe, Mn and Zn contents with increasing soil depth.

Efficiency of multinutrient extractants for the determining of available zinc in soils

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 São Paulo, Brazil, for corn and soybean. All soil samples were limed to increase the CECs 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.

Levels of Heavy metals (Co, Cu, Cr, Ni, Pb, and Zn) in agricultural soils of Northwest Spain

Abstract Soil oxides, pseudototal (aqua regia extracted) and EDTA extractable contents of six potentially toxic metals, namely cobalt (Co), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn) were determined in the topsoil of domestic gardens and agricultural plots in Northwest Spain. The sampled soils were developed over a wide distinct range of geological materials, ranging from felsic to mafic materials, i.e. granite, schist, limestone and mafic and ultramafic rocks. Soil texture varied between sandy‐loam, loam and silty‐loam. Soil oxides were characterised semi‐quantitatively by X‐ray fluorescence, pseudototal contents were determined after digestion in aqua regia, and extractable contents were estimated by extraction in EDTA solution. Pseudototal and EDTA extractable heavy metal contents varied greatly depending on the nature of their parent materials. Soil developed over ultramafic rocks have Cr and Ni contents that exceed current legislative safety limits (NMHPPE, 1991), as a result of high natural concentrations of parent material. There was evidence of anthropogenic contamination by Cu and Zn in some soils, due to the traditional use of animal manures as fertilizers. In soils close to urban centres, there was evidence of Pb accumulation due to atmospheric deposition. The maximum EDTA extractable concentrations were 2.85 mg kg‐1 for Co, 14.7 mg kg‐1 for Cu, 96.9 mg kg‐1 for Ni, 23.2 mg kg‐1 for Pb and 23.5 mg kg‐1 for Zn. The soil contents in EDTA extractable heavy metals were closely correlated with the corresponding pseudototal contents.

Total and Extractable Nickel and Cadmium Contents in Natural Soils

Abstract Trace element analysis in natural soil provides information on background levels, which may be also useful to detect anthropogenic inputs. The main objective of this study was to provide background levels of Cd and Ni for natural soils in Galicia (Spain). Ten natural soil profiles, representative of different parent material with a wide range of elemental composition, including ultramafic rocks such as serpentine, were selected in this region. All samples were digested with nitric acid in a microwave oven (U.S. EPA‐SW 846 305 1 method) to assess “total” Cd and Ni contents. Trace element extractions were carried out with diethylenetriaminepentaacetic acid (DTPA) and Mehlich‐3. All analyses were performed by ICP‐AES. Soil Cd concentrations obtained by the U.S. EPA method ranged from <0.01 to 4.42 mg kg−1, with an average of 2.03 mg kg−1, and Ni concentrations ranged from 12.66 to 2066 mg kg−1 with an average of 156 mg kg−1. The mean Ni content was higher, because the used sample included a soil that was developed over serpentine. The DTPA‐and Mehlich‐3‐extractable Cd and Ni average levels were 0.06 and 8.78 mg kg−1 and 0.16 and 3.57 mg kg−1, respectively. Nickel levels obtained by both extractants were highly correlated (r2=0.91). A correlation analysis between total and extractable Cd and Ni form, and soil general properties showed that the highest significant dependence was for CdDTPA vs. organic matter content and CEC.

Comparison of conventional water testing methods with ion-selective electrodes technique for NO3-, Cl-, Ca2+, K+, and Na+.

Abstract The development of strategies to improve the efficiency of nutrient uptake by crops and to minimise leaching to surface and drainage water needs to be considered at various scales: catchment, field, soil and crop type. Therefore, methodological approaches for routine sample preparation and analysis are crucial to agricultural and environmental policies aimed at reducing nutrient losses. While the official way of analysing water is time consuming and requires a laboratory with standard equipment, the ion‐selective electrodes (ISE) technique presents a method with the advantages of precision, speed and portability. Analysis of water by ISE has become an accepted practice for the detection of certain elements and this technique could replace standard testing currently being used. Accuracy and reproducibility of NO3 ‐, Cl‐, Ca+2, K+ and Na+ ion‐selective electrodes were achieved by comparison with standard methods. The apparatus used consists of a sensor unit, which contains multielement ISEs, and a mesurement unit for operational and data storage functions. Samples of water, obtained from runoff and drainage of agricultural catchments, ground water, were selected from different locations to represent a wide range of ion concentrations. Using the ISE measurements values varied from 0.42 to 83.5 (mg L‐1) for NO3 ‐, 3.89 to 241 for Cl‐, 1.3 to 76.4 for Ca2+, 0.12 to 131 for K+ and 0.63 to 59 for Na+. The investigation confirms the good correlation between standard and ISE methods for almost all ions with correlation coefficients of 0.97 for NO3 ‐, 0.99 for Cl‐, 0.96 for Ca2+, 0.98 for K+. Only Na+ coefficient is below 0.9. Variations in the slope and intercept of the regression equations were slight or small for NO3 ‐ and Ca2+, and larger for Cl‐, K+ and Na+.

Analytical methods and quality assurance

Abstract The development of strategies to improve the efficiency of nutrient uptake by crops and to minimise leaching to surface and drainage water needs to be considered at various scales: catchment, field, soil and crop type. Therefore, methodological approaches for routine sample preparation and analysis are crucial to agricultural and environmental policies aimed at reducing nutrient losses. While the official way of analysing water is time consuming and requires a laboratory with standard equipment, the ion‐selective electrodes (ISE) technique presents a method with the advantages of precision, speed and portability. Analysis of water by ISE has become an accepted practice for the detection of certain elements and this technique could replace standard testing currently being used. Accuracy and reproducibility of NO3 ‐, Cl‐, Ca+2, K+ and Na+ ion‐selective electrodes were achieved by comparison with standard methods. The apparatus used consists of a sensor unit, which contains multielement ISEs, and a mesurement unit for operational and data storage functions. Samples of water, obtained from runoff and drainage of agricultural catchments, ground water, were selected from different locations to represent a wide range of ion concentrations. Using the ISE measurements values varied from 0.42 to 83.5 (mg L‐1) for NO3 ‐, 3.89 to 241 for Cl‐, 1.3 to 76.4 for Ca2+, 0.12 to 131 for K+ and 0.63 to 59 for Na+. The investigation confirms the good correlation between standard and ISE methods for almost all ions with correlation coefficients of 0.97 for NO3 ‐, 0.99 for Cl‐, 0.96 for Ca2+, 0.98 for K+. Only Na+ coefficient is below 0.9. Variations in the slope and intercept of the regression equations were slight or small for NO3 ‐ and Ca2+, and larger for Cl‐, K+ and Na+.

Quest of Water Extract Analysis of Micronutrients in Soilless Organic Substrates

Abstract 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.

Nutrient status on an acid soil as affected by lime amendments after flooding

Rice growth in wetlands or paddy soils is economically important in Latin America, where lime amendment is becoming a conventional practice. A field study was conducted to compare changes induced by liming a rice soil in Corrientes (Argentina). Three different treatments were considered: control, with no lime addition, and two applications of dolomite at rates of 625 kg/ha and 1250 kg/ha. Physico-chemical parameters (Eh, pH) and nutrients (NH4 +‐N, K, Olsen-P and extractable Mn, Fe and Zn) were measured just before flooding and during a ten week period after flooding. At the beginning of the experiment pH ranged between 4.0 and 4.4 and in all the treatments a sharp pH rise was observed from week two to week four after flooding. The initial differences in pH between the control plot and plots amended with dolomite disappeared at the end of the ten week period, when pH conditions were near neutrality. Before flooding, high NH4 +‐N differences between treatments were observed; during anaerobiosis the trend was to increase the low initial NH4 +‐N level of the control plot, whereas the high initial level in the amended plots decreased during waterlogging. Olsen-extractable P was also initially higher in the amended plots than in the control plot and after flooding no unique trend was observed in the three treatments. In all of the treatments, Mn and Fe contents were found to increase during the waterlogging period. Lime enhanced the extractability of these two elements and differences of Mn and Fe levels between control and dolomite amended plots were greater as the flooding period increased.