Soluble element distributions in a Mojave desert soil

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.

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