Manuel Sánchez-Marañón

Colour variation in standard soil-colour charts

This paper presents colourimetric analyses of 6 standard soil-colour charts (1372 chips) from different manufacturers, editions, and degrees of use. The CIELAB hab, L*, and C*ab were found to have significant (analysis of variance, P < 0.05) variations among tested charts, and the Munsell hue, value, and chroma measured in most chips varied from their notation by as much as 1 unit. This discrepancy can be attributed to printing differences and/or colour fading. The Munsell loci of constant hue and chroma plotted in CIELAB colour space showed that colour fading is not uniform, so that visual steps between neighbouring chips change, and constant hue and chroma lines become deformed. The colour difference between chips identically designated in two charts ranged from 0.94 CIEDE2000 units (above perception threshold) for charts from the same manufacturer and degree of use, to 3.72 CIEDE2000 units for old charts from 2 different manufacturers. Chips from old charts became yellowish, darker, and less saturated. These colour changes are consistent with the responses of 10 observers who, on assessing 10 soil-colour samples, reported Munsell notations to have redder hue, lighter value and greater chroma. Periodic colourimetric checking of soil-colour charts would be advisable in order to avoid mistakes in soil-colour description.

Power functions improving the performance of color-difference formulas

Color-difference formulas modified by power functions provide results in better agreement with visually perceived color differences. Each of the modified color-difference formulas proposed here adds only one relevant parameter to the corresponding original color-difference formula. Results from 16 visual data sets and 11 color-difference formulas indicate that the modified formulas achieve an average decrease of 5.7 STRESS (Standardized Residual Sum of Squares) units with respect to the original formulas, signifying an improvement of 17.3%. In particular, for these 16 visual data sets, the average decrease for the current CIE/ISO recommended color-difference formula CIEDE2000 modified by an exponent 0.70 was 5.4 STRESS units (17.5%). The improvements of all modified color-difference formulas with respect to the original ones held for each of the 16 visual data sets and were statistically significant in most cases, particularly for all data sets with color differences close to the threshold. Results for 2 additional data sets with color pairs in the blue and black regions of the color space confirmed the usefulness of the proposed power functions. The main reason of the improvements found for the modified color-difference formulas with respect to the original color-difference formulas seems to be the compression provided by power functions.

Carbonate and Phosphate Precipitation by Saline Soil Bacteria in a Monitored Culture Medium

Carbonate and phosphate precipitation by bacteria isolated from a saline soil was studied in vitro in a liquid culture medium over 45 days. Physicochemical parameters of this medium were continuously monitored using both selective electrodes (continuous monitoring, CM) and individual measurements by other techniques on days 5, 10, 15, 20, 25, 35 and 45 (discontinuous monitoring, DM). In DM, the precipitated minerals were studied (XRD and SEM-EDX) and the saturation index of the mineral phases was analyzed (PHREEQC program). Using the CM and DM data it was possible to distinguish several temporary stages in which both the medium and the mineralogy changed: 1) 0 to 10 days: pH reaches 8.4; significant loss of Mg2+ (incorporated into the bacterial biomass) and Ca2+ (through mineral precipitation); formation of crystals, although not in sufficient quantity to be studied until day 10. 2) 10 to 25 days: pH decreases but remains above 8; appreciable loss of Mg2+ and Ca2+ due to formation of spherical carbonate bioliths with traces of phosphates occluded within these carbonates. 3) After 25 days: biomineralization slow down; pH returns to initial values and struvite is formed (idiomorphic prismatic crystals). These trends are in agreement with the findings of other workers, although with some peculiarities regarding stages and types of mineral precipitated. In some cases the struvite contained small quantities of K and Ca, possibly because these are intermediate mineral species between typic-struvite, K-struvite and Ca-struvite. The bacteria-mediated precipitation of carbonates of Ca and/or Mg and phosphates (struvite) by the bacteria from a saline soil is demonstrated. However, struvite was not found in the soils of origin of the bacteria, possibly because it is a metastable mineral in most soils.

Uniformity of lighting in color assessment cabinets

We have performed spectroradiometric color measurements at different positions on the floor of two lights booths under two light sources. Uniformity provided by these light booths is enough acceptable for most practical color applications involving relative measurements (e.g. CIELAB coordinates), but not for absolute measurements (e.g. tristimulus values or illuminance). Averge color inconstancy indices are lower than 0.6 CIE94 (1.0 CIELAB) color-difference units.

Artificial Neural Networks and Fuzzy Logic for Specifying the Color of an Image Using Munsell Soil-Color Charts

The Munsell soil-color charts contain 238 standard color chips arranged in seven charts with Munsell notation. They are widely used to determine soil color by visual comparison, seeking the closest match between a soil sample and one of the chips. The Munsell designation of this chip (hue, value, and chroma) is assigned to the soil under study. However, the available chips represent only a subset of all possible soil colors, in which the visual appearance for an observer is usually intermediate between several chips. Our study proposes an intelligent system which combines two Soft Computing Techniques (Artificial Neural Networks and Fuzzy Logic Systems) aimed at finding a set of chips as similar as possible to a given soil sample. This is under the precondition that the soil sample is an image taken by a digital camera or mobile phone. The system receives an image as input and returns a set of color-chip designations as output.

Changes in the soil bacterial community along a pedogenic gradient

Current research on the influence of environmental and physicochemical factors in shaping the soil bacterial structure has seldom been approached from a pedological perspective. We studied the bacterial communities of eight soils selected along a pedogenic gradient at the local scale in a Mediterranean calcareous mountain (Sierra de María, SE Spain). The results showed that the relative abundance of Acidobacteria, Canditate division WPS-1, and Armatimonadetes decreased whereas that of Actinobacteria, Bacteroidetes, and Proteobacteria increased from the less-developed soils (Leptosol) to more-developed soils (Luvisol). This bacterial distribution pattern was also positively correlated with soil-quality parameters such as organic C, water-stable aggregates, porosity, moisture, and acidity. In addition, at a lower taxonomic level, the abundance of Acidobacteria Gp4, Armatimonadetes_gp4, Solirubrobacter, Microvirga, Terrimonas, and Nocardioides paralleled soil development and quality. Therefore, our work indicates that the composition of bacterial populations changes with pedogenesis, which could be considered a factor influencing the communities according to the environmental and physicochemical conditions during the soil formation.