Trabal Valentín, Lyvette

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    Physicochemical and mineralogical characterization of four Spodosols profiles in northern Puerto Rico
    (2018-12) Trabal Valentín, Lyvette; Muñoz, Miguel A.; College of Agricultural Sciences; O'Hallorans, Julia M.; Dumas, José A.; Department of Crops and Agro-Environmental Sciences; Valentín, Ricky
    Spodosols are a soil order with clearly distinct soil profile that have a dark surface horizon of organic origin, a bleached, eluvial E horizon, and a reddish, brownish or blackish B horizon, illuvial in nature enriched with amorphous material and organic matter- the spodic horizon. Spodosols are typical of cold and humid climates, and they form under coniferous forests. Four Spodosols profiles were evaluated in Carmen Regadera Farm, Vega Baja, Puerto Rico. The four profiles were described, and soil samples were collected using the horizon sampling method. Soil field texture was sand, loamy sand, sandy loam, and sandy clay loam and consistent with particle size analysis, which showed that the sand content was greater. Soil Aggregates formed in the deepest horizons and stability ranged from 1.12% to 96.9 %. Soil mineralogy of the clay fraction was determined by X-ray diffraction. All four profiles had similar mineralogy consisting primarily of kaolinite, gibbsite, goethite, hematite, quartz and amorphous material. XRD patterns of the B illuvial horizon shows peaks that correspond to aluminum and iron oxide along with kaolinite and amorphous material, when compared to the eluvial horizon that show a spectra that corresponds to quartz. Mineralogical results are consistent with selective dissolution techniques used to determine the Al3+ and Fe3+ from the soil using citrate-dithionite-bicarbonate (CBD) method, ammonium oxalate method (AAO) and sodium pyrophosphate method (SP). Using these selective dissolution techniques, we could determine that the Al3+ content was always greater than the Fe3+ content. The basic cation content was low for three profiles and pH values ranged from 4.16 to 5.19. Profile B showed pH values up to 7.1, possibly due to lateral movement of carbonate enriched water from adjacent areas. The organic matter content determined using the wet oxidation method of Walkley-Black is highest in the surface horizon of the profiles, decreases in the eluvial horizon and accumulates in the B horizon. The fulvic and humic acid from the spodic horizon was analyzed using Infrared Spectroscopy. The fulvic acid spectrum is less complex when compared to the humic acid spectra this shows that the degree of polymerization for humic acid is always higher than for fulvic acids. The spectra of humic and fulvic acids suggest that chelation occurs between functional groups and oxides and silicate minerals. Strong physical, chemical and mineralogical evidence exist within the four Spodosols profiles studied to show that the pedogenetic process of podzolization is manifested and soil properties are consistent with that of the Spodosols soil order. Differences in physical and chemical properties of the profiles evaluated suggest that these soils belong to the great groups Typic Alorthod and Typic Alaquod.