New Mexico Geological Society Annual Spring Meeting — Abstracts

In 1899 when the Pecos Valley Soil Survey was published, it was one of the first 4 surveys published in the US. In that era, soils were classified based on their parent material and texture. By 1917, Curtis Marbut had translated from German the work of Glinka and brought the concepts of Russian pedologists to the US; namely, that bioclimatic factors, given time, produce pedogenic horizons, and these, rather than parent material, should be the basis of soil classification. By 1960, soil genetic horizons had become the foundation for classifying soils in the US, which was formalized as the 7^th Approximation, then, after much further testing, became “Soil Taxonomy” published in 1975. Thus, soil horizons, especially those based on soil organic matter, silicate clay, and pedogenic carbonate, are specific indicators of past climates, and consequently can be used as predictors of the soils of New Mexico in the future.

Although there are exceptions to each of the statements below about the soil orders in New Mexico, in general we can say that (1) Aridisols and (2) Entisols are the “desert soils” with Aridisols being those soils with pedogenic development. Entisols, while occurring in the aridic moisture regime, can also transcend it into semiarid climates and are thus “azonal” soils whose main characteristic is the absence of significant pedogenic development. (3) Mollisols are the soils with organic-rich mineral topsoil horizons formed in grasslands and those forests with partially open canopies and thus herbaceous understory. (4) Alfisols are the soils with illuvial clay accumulation occurring mainly in the forests and plains of NM. (5) Inceptisols are less pedogenically developed than Alfisols. Incepitisols can also occur in forests, especially on steep slopes too geomorphically active or too young for illuvial clay, but they occur mainly as the soils with intermediate development in the semiarid plains. (6) Andisols are the volcanic ash-derived soils having unique clay mineralogy and bulk densities in the Jemez Mountains. (7) Histosols are the organic soils in the Sangre de Cristo’s) occupy small areas with high water tables and anaerobic conditions. Lastly, (8) Vertisols are shrinking-swelling soils that occur in both arid and semiarid climates of NM in the clayey deposits of many playas, many abandoned oxbows of river floodplains, and many shale parent materials of the Colorado Plateau.

Because each of the soil orders carry a “memory” of past climates, each order can be used to predict how it will respond to future climates. Mollisols, in particular, will lose much of their organic carbon as Aridisols expand at their expense. Perhaps, however, some of that carbon lost from organic matter will be sequestered as pedogenic carbonate in zones currently too humid for carbonate formation.