Pérez Lizasuain, Bianca

Profile Picture

Filters

20121
Reset filters

Settings

Citations

Publication Search Results

Now showing 1 - 1 of 1
  • Thumbnail Image
    Publication
    Presence, quantification and analysis of ironstone in a Guanajibo soil profile
    (2012) Pérez Lizasuain, Bianca; Muñoz, Miguel A.; College of Agricultural Sciences; Lugo, Wanda; O’Hallorans, Julia M.; Department of Agro-Environmental Sciences; Gilbes, Fernando
    Plinthite is defined as a weakly cemented material rich in iron, poor in humus –a mixture of clay and other diluents, such as quartz. It commonly occurs as dark red redox concentrations that can change irreversibly to ironstone hardpans or irregular aggregates on exposure to repeated wetting and drying. The presence of this material may affect plant root growth, soil fertility as well as soil drainage, acidity, and management. The studied soil belongs to the Guanajibo series and is located in the municipality of Cabo Rojo, Puerto Rico. The objectives of this study were: (i) determine soil layers color and ground ironstone colors and relate these to mineral components; (ii) quantify on volume and mass bases the presence of ironstone in each soil profile; (iii) determine mineral components in ironstone and soil by x-ray diffraction (XRD) and determine the content of iron and aluminum from each horizon by extracting the soil and grounded ironstone by two distinct methods: citrate-bicarbonate dithionite (CBD) and ammonium oxalate (OX). The CBD method extracts the crystalline fraction of the iron while the OX method removes the iron complexes with organic matter and amorphous iron. We suggest that reddish 10R and 5YR are associated to the presence of hematite and reddish yellow (2.5YR to 7.5YR) are associated with the presence of goethite. The highest content of ironstone was found in the upper horizon Ap, with a reduction in the next two lower horizons Bt and Btv1. An increase was observed in horizon Btv2 indicating that the soil was formed by alluvial deposits. The content of iron oxides and the effective cation exchange capacity (ECEC) were related to the clay content of each horizon. Higher clay content coincided with higher iron oxides content and higher ECEC. The opposite was observed for aluminum oxides content. The ECEC was low in all horizons, indicative of the presence of highly weathered minerals. This finding was confirmed by XRD analysis, showing minerals such as kaolinite, goethite, quartz, hematite and gibbsite. The main component of ironstone was goethite and the main component of the soil was kaolinite. Each horizon was classified as plinthic or not plinthic following the requirements established by the USDA- Natural Resources Conservation Service: the soil fine-fraction must have more than 2.5% of iron in the CBD extraction, and a ratio between OX and CBD extractable iron (OX/CBD) of less than 0.10. Of the five horizons only Btv1 was classified as plinthic, showing 2.8% CBD extractable iron and a ratio less than 0.10. The other horizons met with the requirement of a OX/CBD ratio less than 0.10, but all had less than 2.5% of iron extracted by the CBD method.