In this paper, the production of humic substances (HS) through the bacterial solubilization of low rank coal (LRC) was evaluated. The evaluation was carried out by 19 bacterial strains isolated in microenvironments with high contents of coal wastes. The biotransformed LRC and the HS produced were quantified in vitro in a liquid growth medium. The humic acids (HA) obtained from the most active bacterial strain were characterized via elemental composition (C, H, N, O), IR analyses, and the E4/E6 ratio; they were then compared with the HA extracted chemically using NaOH. There was LRC biotransformation ranged from 25 to 37%, and HS production ranged from 127 to 3100 mg.L−1. More activity was detected in the isolated strains of Bacillus mycoides, Microbacterium sp, Acinetobacter sp, and Enterobacter aerogenes. The HA produced by B. mycoides had an IR spectrum and an E4/E6 ratio similar to those of the HA extracted with NAOH, but their elemental composition and their degree of aromatic condensation was different. Results suggest that these bacteria can be used to exploit the LRC resulting from coal mining activities and thus produce HS in order to improve the content of humified organic matter in soils.

Background: This study assessed, under greenhouse conditions, the use of low-rank coal (LRC) generated in the "El Cerrejón" (La Guajira Colombia) mine as a source of humified organic matter, which is released by the activity of coal solubilizing bacteria (CSB), in order to improve the properties of edaphic materials (EM) used in post-mining land reclamation processes. Methods:In this trial, using pots with 10 kg of EM, the effect of LRC applications was tested, in contrast with applications of LRC inoculated with CSB at two different doses and EM without LRC. The responses of the cation exchange capacity (CEC), soil respiration, and fluorescein diacetate hydrolysis (FDA) were evaluated in each treatment. The contents of P and N and the dry weight were measured in maize seedlings. Soil microaggregates were observed with scanning electronic microscopy. Results:After 12 months of treatment with LRC, an increase of 75 % was registered in the CEC, along with an increase of up to 59 % in the EM respiration (CO 2 production) and up to 50 % in the FDA activity. The LRC caused a significant increase in the dry weight and the total contents of N and P in the maize seedlings; the observations with the scanning electronic microscopy showed evidence of the formation of bigger aggregates, as compared to the control, and the presence of organic material on mineral particles in the treatments with LRC inoculated with CSB. Conclusions:These results provided evidence that supports the use of LRC, alone or inoculated with CSB, as a humic amendment to improve the EM in soil reclamation processes (Technosols construction) after mining activities.

BACKGROUND: Cadmium uptake by cacao plants can affect plant growth, consumer health and commercialisation. To develop mitigation strategies, it is essential to identify the soil characteristics that could influence this absorption. To determine the relationships between cadmium absorption and the soil characteristics of cacao areas, the responses at concentrations of 0, 2, 5, 10 and 20 ∼g g −1 of cadmium in three soils of these areas and an andisol were evaluated, using 120-day-old seedlings of four cultivars of Theobroma cacao L.RESULTS: In the present study, several relationships were found between chemical and physical soil characteristics and available cadmium, such as real and bulk densities, as well as contents of iron, sand, magnesium, potassium, sodium and copper. Additionally, moderate to strong correlations between potassium (r 2 = −0.56) and real density (r 2 = 0.42), with foliar cadmium, were found. Moreover, a differential deleterious effect on cacao growth in variables such as biomass was corroborated in cadmium concentrations from 5 ∼g g −1 in soils. There were no statistical differences between cultivars with respect to cadmium uptake or plant growth. Finally, a multiple linear regression model is proposed to estimate the foliar cadmium content (r 2 = 0.878).CONCLUSION: Some soil characteristics such as density, as well as sand, clay, aluminium, potassium and iron contents, should be considered before establishing cacao crops to avoid cadmium accumulation. The correlation between potassium with foliar cadmium indicated that potassium could be significant in cadmium uptake mitigation strategies. The high correlation between available cadmium and foliar cadmium indicates that the quantification methodology developed using ethylenediaminetetraacetic acid extractant may be a useful diagnostic tool.

Este estudio se centra en evaluar el impacto de la adición de carbón de bajo rango en la conductividad térmica, humedad del suelo y el crecimiento del maíz (Zea mays) en suelo de tipo salino sódico recolectado en el Departamento del Cesar, Colombia. Se preparan muestras (2 kg) de suelo con proporciones de 0, 2 y 4 t/ha de carbón de bajo rango y se siembra maíz variedad ICA 109 procedente de Colombia. La conductividad térmica del suelo se mide in situ 10 días después de establecer el experimento. Los resultados muestran que la adición de carbón de bajo rango causa un descenso significativo en la conductividad térmica del suelo y una supervivencia de las plantas de maíz del 36%. Se concluye que la dosis media (2 t/ha) de carbón de bajo rango es la más eficiente en promover el crecimiento de plantas.

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