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FOREST, RANGE & WILDLAND SOILS

Soluble Element Distributions in a Mojave Desert Soil

Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512

^* Corresponding author (giles.marion{at}dri.edu).

The distribution of chemical species in desert soils is a complex function of atmospheric inputs, rock weathering, chemical equilibria, soil leaching, and plant cycling. In this study of the surface 1 m of desert soils at the Nevada Test Site, we examined the distribution of soluble soil elements beneath plant canopies and in intershrub zones. We extracted water-soluble chemical species using saturation extracts that were equilibrated overnight and more dilute extracts that were incubated for 1 mo. All soil horizons were supersaturated with calcite and undersaturated with gypsum. Calcite supersaturation was a function of soil organic C (inhibitor) and water content (inhibitor diluent). It is critical that the latter two properties be explicitly recognized in modeling CaCO₃ mobility through soils. Plant-essential cations (K, Ca, and Mg) were highest in concentration in surface soils beneath plant canopies. Sodium, Cl, NO₃, and SO₄ were generally highest in concentration around 1-m depth. The dissimilar patterns of essential nutrient accumulations between the cations (Ca, K, and Mg) and the anions (NO₃ and SO₄) were probably due to the greater mobility of anions than cations. Also, these surface soils were "N saturated" due to their low N retention capacity, which accounts, at least in part, for the anomalous NO₃ accumulations at depths >1 m in Mojave Desert soils. Furthermore, once NO₃ or SO₄ have leached to deeper soil depths, they may be relatively unavailable for plant uptake. The soil elemental patterns are consistent with elemental plant requirements and elemental mobility.

Abbreviations: IAP, ion activity product