Mauricio Molina

Trace Element Composition of Selected Fertilizers Used in Chile: Phosphorus Fertilizers as a Source of Long-Term Soil Contamination

Anthropogenic activities like agriculture have resulted in increased concentrations of some trace elements of toxicological and environmental concern in soils. Application of fertilizers has been one of the major inputs of these contaminants to agricultural soils in developing countries. Twenty-two fertilizers, including straight nitrogen (N), phosphorus (P), potassium (K), and NK fertilizers and micronutrient sources, were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) for arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn). As expected, the trace element content of fertilizers was highly variable and related to the origin of the material. Phosphorus fertilizers, especially triple superphosphate, presented the highest As, Cd, Cu, Cr, Ni, V, and Zn concentrations. In some of these fertilizers, the Cr, V, and Zn contents reached values greater than 3475 mg kg−1 of P, and the Cd content (up to 288 mg kg−1 of P) was several times higher than the regulatory limits of different countries. Some micronutrient sources presented the highest concentrations of Mn and Pb. In the cases of N, K, and NK fertilizers, the trace element concentration was very low, sometimes below the detection limits. In some agricultural systems the input of trace elements such as As and Cd to the soil through P fertilizers application may be higher than the outputs through plant uptake and leaching; therefore the long-term use of these fertilizers may cause the trace element concentration to increase in the plow layer of agricultural soils.

Impact of forest fire ash on surface charge characteristics of Andisols

Forest fires are a common occurrence in central southern Chile where soils are mostly Andisols. The ash deposits may alter the chemical properties of the soils in the burned areas and nearby agricultural lands. In a column experiment, three Andisols found in this region were treated with 2-cm-thick ash deposit on the surface and leached with 12 pore volumes of water for 3 months. At the end of the leaching, the ash-treated and their respective control soils were sectioned, and the surface charge characteristics of each soil section were determined by electrophoretic mobility test and potentiometric titration. Chemical constituents released from the ash affected mainly the surface 0- to 5-cm section of the soils. The ash treatment and leaching caused the soil pH of the 0- to 5-cm section to increase from 2 to 3 pH units. Consequently, the negative surface charge and cation exchange capacity of affected soils both increased. The ash treatment changed the isoelectric point when the isoelectric point of respective control soil section was >3. The point of zero salt effect and the point of zero net proton charge of the ash-treated soils were increased in the 0- to 5-cm section and the influences of the ash leachates gradually diminished with soil depths. The alkaline leachates dissolved and mobilized the soil organic carbon and associated soil constituents. The effects observed on the surface charge and dissociation constants are consistent with anion and/or dissolved organic carbon adsorption. The surface dissociation constants, estimated by the constant capacitance model, showed that the ash treatment caused modifications of the active sites on the soil particles. Although ash leachates increase the cation retention capacity, the adsorption of other cations may be adversely affected by the ash deposit that is rich in Ca2+ and K+.

Evaluation of the AB-DTPA multiextractant in Chilean soils of different origin with special regard to available phosphorus

The objective of this study was to evaluate the suitability of the ammonium bicarbonate diethylenetriaminepentaacetic acid (AB-DTPA) multiextractant to estimate the available P, exchangeable cations (K, Ca, Mg, Na) and extractable micronutrients (Cu, Fe, Mn, Zn) in comparison with conventional soil tests (Olsen-P, NH4OAc-exchangeable cations and DTPA-extractable micronutrients) in alkaline, acidic and volcanic acidic soils (n = 50). Exchangeable cations and extractable micronutrients were determined in soil extracts by ICP-OES. Phosphorus was determined colorimetrically in Olsen extracts, while in AB-DTPA extracts, P was determined both colorimetrically (AB-DTPAC-P) and by ICP-OES (AB-DTPAICP-P). In 14 soils, the available soil and plant P were determined in a pot experiment with ryegrass (Lolium multiflorum L). Both the AB-DTPAC-P and AB-DTPAICP-P were highly correlated with Olsen-P in alkaline and acidic soils. All P extractants were highly correlated with plant P concentration and uptake, but in soils with Olsen-P <20 mg kg−1 the AB-DTPA-P showed weaker relationships with P availability. The AB-DTPA method can be recommended to estimate the available P in alkaline and acidic soils, excluding Andisols, which typically contain very low amounts of available P. For K, Mg, Na, Cu, Fe, Mn and Zn, the multiextractant was highly correlated with respective conventional tests in all soils.

Sorption and selectivity sequences of Cd, Cu, Ni, Pb, and Zn in single- and multi-component systems in a cultivated Chilean Mollisol.

The heavy-metal sorption ability of soils is one of the most important factors that determine the fate of these contaminants in this medium of the biosphere. When heavy-metal containing soil amendments are land applied, a multi-component soil-solution equilibrium may occur in which various metals compete simultaneously for the sorption sites on the soil particles. In order to determine the effect of competition among Cd, Cu, Ni, Pb, and Zn on sorption characteristics and the selectivity sequence of those heavy metals in a cultivated Mollisol of central Chile, batch sorption experiments were carried out in single- and multi-component systems. Heavy metal sorption isotherms in both types of system were well described by the Langmuirs equation. For all the metals evaluated, competition among them (multi-component system) decreased both the maximum sorption capacity, obtained from the Langmuirs isotherm, and the partition coefficient (Kd) compared to the single-component system. In addition, the simultaneous presence of the five metals promoted the sorption of Cd, and to a lesser extent of Ni, on more specific sorption sites of soil particles. Either in single- or multi-component system, Pb and Cu showed a higher selectivity and retention compared to Cd, Ni and Zn, which indicates that the later heavy metals would present a higher mobility in the soil-plant-water system. Since Langmuirs parameters and Kd were highly affected by competition for all heavy metals evaluated, the use of single-component parameters in modeling assessment might lead to an incorrect description of the transport and fate of these contaminants in receiving Mollisols.

Effect of ash from forest fires on phosphorus availability, transport, chemical forms, and content in volcanic soils

Environmental context. Intensive fertilisation and the availability of phosphorus species (less than 10%) in cultivable soils of volcanic origin are causing the accumulation of P in these soils. Phosphorus is a macronutrient that severely limits good agricultural development, so knowledge of the distribution and the different forms of P present in soils is fundamental for sustainable agricultural practice. This novel study reports the existence of increased available P in all the soils that received a load of plant ash from different tree species. Abstract. The effect associated with the distribution of ash from plantations of native, pine, and eucalyptus forests over five soils of volcanic origin was studied by means of column leaching experiments. The results show a clear increase of pH (up to 4.4 units) and of the soil’s electric conductivity (up to 21 times), whereas total extractable P content increased 3 to 10 times with respect to the control. These effects follow a sequence depending on the origin of the ash (native forest, pine, eucalyptus), concentrated in the 0.0–10.0-cm section from the top of the columns. The observed alkalinity caused an increase of available P (from 21 to 72 times with respect to the control), in addition to decreasing residual P and increasing the extraction efficiency of the method used, discarding a transformation of inorganic P into organic P. Finally, the results show that the addition of ash is a valid and complementary alternative to phosphate fertilisation.