Detailed soil survey of the Jornada LTER (Long Term Ecological Research) transect vicinity, southern New Mexico

TitleDetailed soil survey of the Jornada LTER (Long Term Ecological Research) transect vicinity, southern New Mexico
Publication TypeThesis
Year of Publication1995
AuthorsRojas AEncina
Date Published1995
UniversityNew Mexico State University
CityLas Cruces, New Mexico
Thesis TypeM.S. Thesispp
Accession NumberJRN00187
Call Number00732
Keywordsdissertation, dissertations, soil carbon, soil mapping, soil properties, soil survey, soil texture, soil, aridisols, soil, boundaries, soil, cambic horizon, soil, classification, soil, description, soil, geomorphology, soil, K horizon, soil, landscape, soil, morphology, soil, organic carbon, soil, spatial variability, theses, thesis
Abstract

This study presents a detailed soil map of the upper portion of the Jornada LTER site on the bajada between Summerford Mountain and College Playa. It also offers an explanation why some dark soils in the Summerford grassland give a false impression of high organic matter. The purpose of this study is to help LTER scientists better understand the flora and fauna distribution on the LTER site, which are greatly affected by soil variability. The study consisted of two parts: the field study and the laboratory analysis. For the field study, aerial photography was used in conjunction with field observations, which included describing soil profiles in hand-dug pits and with a soil auger. Data for laboratory analysis were collected from 17 pedons along the upper LTER I transect, which extends from the Summerford grassland at the base of the northern Dona Ana Mountains downward tothe New Mexico State University College Playa. Laboratory analysis included organic carbon, calcium carbonate, particle size distribution and pH. The 17 sites were selected based on topography, soil color and vegetation patterns. Seven pedons were placed in the Summerford grassland area and compared to ten pedons downslope from the grassland along the LTER transect. In addition to the aridic moisture regime criterion, soils were classified based on the presence of the following diagnostic horizons: mollic, ochric, cambic, argillic and calcic. Two soil order were classified in the study area: Mollisols and Aridisols. Mollisols occur in the upper part of the Summerford grassland where mollic epipedons occurs as deep A horizon with high accumulation of organic matter. They include Aridic Haplustolls, Aridic Argiustolls, and Torriorthentic Haplustolls. Aridisols occur downslope where shrubs become more predominant. These include Typic Haplargids, Typic Haplocambids, Typic Haplocalcids, Ustic Haplargids and Ustic Haplocambids. For the family differentiate, all pedons described have a coarse-loamy particle-size class. The mineralogical and the soil temperature classes are mixed, thermic based on correlation to previous studies. To determine why some soils in the Summerford grassland had a false impression of high organic carbon content, thin sections were made by impregnating peds with blue-epoxy, and observing them with a polarized microscope. The false impression of high organic carbon content was found to be a result of most of the organic matter occurring as a thin coating on gravels and sand grains with very low organic matter in the pore spaces. Although the coating make up a small percentage of soil by weight, they effectively darken the horizon.