Saturday, 15 July 2006

Comparison between Humic Extract Color by Reflection and Transmission in Two Mollisols.

Ana-Patricia Fernandez-Getino, DPTO. Edafologia E.T.S.I. Agronomos, Univ Politecnia De Madrid, Avda. Complutense, S/N, Madrid, 28040, Spain, Jose-Maria Gasco, DPTO. Edafologia E.T.S.I. Agronomos, Univ Politechnica de Madrid, AVDA. Complutense, S/N, Madrid, 28040, Spain, and Francisca Guerrero, Univ. de Madrid, Madrid, 28040, Spain.

The dark color of the soils is commonly related to the organic matter content. In this research the reflected and transmitted colors of total humic substances (THS) were determined by chromameter and spectrophotometer measurements. Three color systems were applied to determine the color of samples from two Calcic Argixerolls. The Munsell color system, the CIEYxy-1931 color system and a method based on spectrophotometer measurement. Soils are located in Spain, one in the Páramo of Madrid and the other one in the Alcarria region, both of them on limestone. The Mollisols of the Páramo and the Alcarria regions, which have a mollic epipedon, although they are covered by the same type of vegetation (Quercus ilex sp. Rotundifolia), are found at a different altitude, so the climate conditions vary, and this influences the soil properties.Reflected Munsell hue value/chroma (H V/C), and CIE-Yxy-1931 lightness (Y) and chromaticity coordinates (x,y) of THS were determined through the bottom of a Petri box (transmittance of 99 %) by Minolta Chroma Meter CR-200. The Petri box was covered with a black mask to avoid external lightness. Transmitted color of THS solution was related to the absorbance measurements by Spectrophotometer Shimadzu UV-1203 at the different wavelengths of the visible spectrum (from 350 to 800 nm) by steps of 5 nm. Color by reflection and transmission were measured in THS extracted with a mixture of Na4P2O5 and NaOH. The ratio soil/solution (w/v) was adequate considering their respective organic matter contents.

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