Baseline values and environmental assessment for metal(loid)s in soils under a tropical rainy climate in a Colombian region

The baseline values for metal(loid)s in soils are known as a tool for the evaluation, prevention, and monitoring of the environmental quality of the soil. The main aim is to propose baseline values for metal(loid)s through the analysis of the concentrations in soils within natural areas; additionally, this study attempts to assess the environmental quality of soils in agricultural areas. The study was developed in the Piedemonte Llanero from Colombia a region with more than 5000 mm year^-1 of pluviometry. A total of 90 soil samples were collected in agricultural and natural areas. Chemical analysis was conducted by acid digestion following the method EPA 3050B and determined the metal(loid)s (Al, As, Fe, Cd, Cr, Cu, Mg, Mn, Ni, Pb, and Zn) through ICP-OES. This is the first time that baseline values are proposed for a region in Colombia. The values proposed (expressed in mg kg^-1) are Cd (0.3), As (2.8), Cu (9.9), Ni (10.2), Pb (11.3), Cr (21.1), Zn (28.2), Mn (83.8), Mg (348), Fe (22,775), and Al (28,975). These values are comparatively lower than those reported for other regions in Latin America and the rest of the world. Also, agricultural soils are not contaminated. The possible explanation is as a consequence of the intense washing caused by the intense rainfall of the place. The results also demonstrated that the soils in this region are not contaminated. Finally, these advances will allow public and private organizations to establish criteria for the environmental and sustainable management of soils, especially on agricultural activities.

Incidence of bacterial diseases associated with irrigation methods on onions (Allium cepa)

BACKGROUND

In the last decade, diseases of bacterial origin in onions have increased and this has led to significant losses in production. These diseases are currently observed in both the Old and New Worlds. The present study aimed to evaluate whether the irrigation method influences the incidence of diseases of bacterial origin.

RESULTS

In cases where the inoculum was natural, the initial incidence of soft bacterial rot did not manifest in any treatment in the first year, whereas, at the end of the conservation period, all treatments had increased incidences of infection. Sprinkler irrigation (8%) was statistically differentiated from the other treatments, for which the final incidence was similar (4.5%). For all irrigation treatments, the final incidence of bacterial soft rot decreased or remained stable towards the end of the cycle, with the exception of sprinkler irrigation in 2015, which increased.

CONCLUSION

From the results of the present study, it can be inferred that the irrigation method does have an influence on the incidence of diseases of bacterial origin in the post-harvest stage for onions. © 2018 Society of Chemical Industry.

Chemical vulnerability of red soils in La Mancha (Central Spain)

Red soils are widely distributed in Mediterranean regions. They constitute one of the most important soil resources for crop production and other uses. The main objective of this paper is to estimate the inherent chemical susceptibility of red soils of La Mancha to chemical degradation. Selected 47 soil profiles, were analyzed in the area by means of multivariate analysis; we identified five soil attributes that are well represented in the local soils database, which are most likely to control the chemical vulnerability. These attributes are the calcium carbonate, organic matter and clays together with soil depth and drainage. The attributes were transformed and a simple vulnerability index (VI) was deviced. We concluded that the index may be used as a first approximation rating of La Mancha's red soils vulnerability against an eventual chemical degradation, or to aid resource management and prevent anthropogenic potential impacts.

Humus quality after eucalypt reforestations in Asturias (Northern Spain)

The impact on soil properties of recent and ancient reforestations with Eucalyptus globulus Labill. has been studied in Cambisols and Leptosols under temperate semi-oceanic climate in Asturias (Northern Spain). Eucalypt forests showed a high potential of C accumulation in soil, mainly the ancient forest, where the organic matter concentration in the uppermost horizon (up to 415 C g x kg(-1)) was greater than in all neighbouring soil formations (climacic oak forests, up to 84 C g x kg(-1); Podsol under reforested pine forests, 287 C g x kg(-1); and Ulex shrub, 70 C g x kg(-1)). Nevertheless, there was a low concentration of available bases and a very low transformation degree of the organic matter in this eucalypt forest, only comparable to that of the Podsol. In order to analyse the major features of the biogeochemical behaviour of the sites under study, the humus fractions were isolated and the humic acid fraction was studied by derivative visible and infrared spectroscopies. Incubation experiments on whole soil samples were carried out to monitor stability against biodegradation of the organic matter under comparable conditions. In general, soils under eucalypt had a CO(2) production similar to or lower than the control sites, but the soil under the ancient eucalypt forest had a high potential for CO(2) release, similar to that of the neighbouring Podsol, what might be explained by the presence in these soils of high amounts of C accumulated in readily biodegradable forms. However, the mineralisation coefficients (CO(2) released per unit of soil C) indicated that the biodegradability of the soil humus has decreased significantly in the eucalypt-reforested sites, as it could correspond to an effective control of the biogeochemical processes caused by the antimicrobial products from the eucalypt litter. Compared to the original deciduous forests, the lower values of the E(4)/E(6) ratio in the humic acids from eucalypt forests and the lignin signature in the infrared spectra point to humification mechanisms based on the selective preservation of complex macromolecular substances derived from vascular plants. The second derivative of the visible spectra of the humic acid samples under study showed conspicuous valleys, which are ascribed to fungal-derived 4,9-dihydroxyperylene-3,10-quinone pigments. These valleys were in most eucalypt forests significantly shallower than in the original deciduous forests and may also represent an indicator of the impact of introduced vegetation on the structure of the soil microbial system and the mechanisms responsible for the formation of humic acids.