Desert soils differ from those of wetter regions by, among other things, a deficit of biologically available nitrogen that often is a factor limiting plant growth. A recent study of chloride in desert subsoils thus evoked surprise when it also turned up large accumulations of nitrate. Nitrate is one of the few nitrogen-containing molecules that is available for use by plants, but the newly found accumulations lie below the root zone of most plants.
Traditional knowledge holds that plants quickly use available nitrogen, leaving little or none to leach into lower levels. Obviously wrong. The new hypothesis is that nitrate began accumulating as the climate dried out toward the end of the ice age. Carried downward by occasional heavy precipitation, the nitrate was stranded as plants and surface evaporation sucked moisture upwards. Current accumulations are the result of some 10-16 thousand years of such leaching.
A potential problem is that if moisture increases due to irrigation or
climatic change, ground water supplies may well become contaminated with the nitrate.
Once again, the desert shows how little we understand it!
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.