Soil climate indicators from the Geographically Explicit Newhall Simulation Model (GEN) as potential environmental covariates in digital soil mapping applications

Abstract

Historically, the NSM has been used to aid U.S. Soil Survey research by providing categorical output for soil moisture and temperature regimes. Terminology for soil moisture regimes includes categories such as Udic, Aridic, Ustic, Xeric, and Aquic, which indicate varying levels of seasonal or annual moisture conditions (Soil Survey Staff, 1999). In order to provide classifications for particular soils the NSM populates a calendar of soil moisture and temperature status for the calendar days of a year or set of years of interest. The NSM can provide monthly and annual summaries of soil climate status, modeled at the depth of the taxonomic soil moisture control section of U.S. Soil1 INTRODUCTIONThe Newhall Simulation Model (NSM) has been used by the U.S. Soil Survey and in international soil mapping efforts for more than 50 years (Smith, 1982; Newhall and Berdanier, 1996; Waltman et al., 2012). NSM provides categorical output useful in U.S. Soil Taxonomy, is simple and flexible and does not require extensive model inputs. For inputs it uses monthly air temperature and precipitation values, elevation, a programmable offset between annual air temperature and annual soil temperature, and available water holding capacity of soils. The purpose of the NSM is to classify soils according to their dominant soil moisture and temperature properties based on rudimentary estimates of evapotranspiration, drainage, and the effects of air temperature and precipitation on soil moisture and soil temperature characteristics. While the modelTaxonomy, including soil climate variables such as cumulative days in a year the soil is dry, or partly moist and partly dry, or moist, or dry and above 5°C, or partly moist partly dry and above 5°C, or moist and above 5°C; the consecutive days in a year that the soil is moist, or above 8°C and moist; and finally the consecutive days in the summer that a soil is dry or the consecutive days in the winter that the soil is moist. These outputs are needed in order to classify soils in the U.S. Soil Taxonomic system (Soil Survey Staff, 1999).