Residual Nitrogen In Parent Materials 

 of West Side Soils 



Genesis and Morphology . The composition of parent rock* is 

 an Important factor In determining soil characteristics In 

 an area of arid climatic conditions, such as the west side 

 of the San Joaquin Valley. The rocks of the Diablo Range, 

 from which all the soils In the study area except the basin 

 soils of the area have been derived, are classed geologi- 

 cally as a series of sandstones, shales, and conglomerates 

 of Cretaceous and eairllest Tertiary (Eocene) age (6). It Is 

 from these formations that parent materials of west side 

 soils have developed. 



Soils associated with certain drainage ways of the coastal 

 foothills contain varying quantities of salts, such as 

 gypsum, calcium carbonate, and sodium carbonate. Only in 

 the last few years has Interest In nitrates in subsurface 

 and ground waters developed. Consequently, data on quantity 

 and quality of nitrates are scarce. As related previously 

 in this report, several instances of high nitrates have been 

 found in certain alluvial soils which cannot be accounted 

 for by fertilization. Existing concentrations in these 

 profiles vary according to the extent of leaching caused 

 either by natural stresuns or by recent irrigation. 



Nitrogen Concentrations in Parent Materials 



To better understand the persistence of native or residual 

 nitrogen, one must realize that these soil profiles have 

 developed in a relatively drv environment (6 to 8 inches 

 total precipitation per year). Flash storms produced many 

 mud flows; Intermittent streamflow, which carried heavy 

 loads of fine material, subsequently deposited this material. 

 Periods of flooding were followed by periods of rapid 

 evaporation, which allowed little time for deep percolation. 



This developmental process was quite clear to Agricultural 

 Research Service Investigators during their deep boring 

 studies (15). Findings at two of these plots in Panoche 

 soils promoted investigations of parent materials in old 

 drainage ways of the Diablo Range, which were presumed to be 

 the source of the alluvium. Samples were collected from 

 several sites in three main arroyos: Clervo, Hondo, and 



♦Parent materials are defined (?) as the unconsolidated and 

 more or less chemically weathered mineral or organic matter 

 from which the solum of soils is developed under pedogenlc 

 processes . 



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