1914] Loughridge: Humus and Nitrogen in Calif ornia Soil Columns 247 



SOIL COLUMNS OF THE "DESERT" PLAINS 



The term "desert" is here applied to the extent of country 

 with scant rainfall and having a vegetation of sagebrush and 

 largely devoid of grasses; a country whose soils are usually rich 

 in the mineral elements of plant food and which are remarkable 

 for their fertility when properly cultivated and abundantly 

 irrigated. The reason for this fertility lies partly in the fact 

 that the humus, though small in amount, is with its nitrogen well 

 distributed throughout a depth of twelve feet and more, in a soil 

 whose sandy or silty texture permits deep rooting of plants. 



The desert lands are interspersed with mountain ranges 

 separated by valleys of greater or leaser extent. Some of these 

 valleys have with irrigation been brought under cultivation and 

 settlement and from these a few soil columns were secured. 



Imperial Valley. — This newly settled part of the state, once 

 the bed of Salton basin which on drying-up became a desert 

 until reclaimed by irrigation, largely lies below the level of the 

 sea. Its soils, derived from the sediment of the Colorado River, 



Table 41. — Humus in Soil Columns of Imperial Valley, 

 Imperial County 



Kange of most annual plant roots. 



