Residual Nitrogen in West Side Soils 



Background 



The presence of nitrogen was Investigated In various soil 

 profiles along the west side of the San Joaquin Valley floor, 

 and these findings correlated rather well with concentra- 

 tions of nitrogen observed In tile drainage discharge of 

 similar soils. The following points were the basis of such 

 correlation. 



1. Nitrogen concentrations in tile drainage from alluvial 

 soils were higher than in drainage from other physio- 

 graphic positions investigated; in many cases, nitrogen 

 yields exceeded fertilizer applications, 



2. Findings by other investigators presented strong 

 evidence of native or residual nitrogen in certain soils. 



This phenomenon was first reported by Dyer (20), whose data 

 showed that nitrogen concentrations lying as deep as 25 to 

 50 feet in a virgin Panoche soil near the Coast Range foot- 

 hills exceeded 1,400 milligrams per liter. Doneen (26) 

 observed high nitrates in shallow ground water in Irrigated 

 Panoche and Oxalls soils. Later, Doneen, et al (27), in an 

 economic study on the potential agricultural development of 

 new lands in the southwest San Joaquin Valley, again 

 observed high nitrate-nitrogen levels in virgin Panoche and 

 Panhlll soils. Deep boring investigations (15) conducted 

 by the Agricultural Research Service showed moderate to high 

 nitrate values at depths of 20 to 60 feet in west side 

 Panoche soils which were farmed. Nitrate values in Hesperla 

 and Tujunga soils, which are located on the east side of 

 the Valley, were significantly lower in nitrates at greater 

 depths (Figure l6). Three tile drainage systems located 

 along the east side of the Valley, but in different loca- 

 tions than the plots mentioned above, also showed evidence 

 of low nitrogen concentrations. These systems, which were 

 not actually included in the regular nutrient monitoring 

 program, were monitored periodically from June through 

 December 1967; the combined drainage averaged 10 mg/l 

 nitrate-nitrogen. Quantities of nitrate in terms of pounds 

 above the water table were determined at separate borings 

 for each plot. The data are Illustrated in Figures 17 and 

 l8. From these investigations, the ARS determined that 

 fertilizer application could not possibly account for the 

 large amounts of nitrates found in the west side Panoche 

 profiles. 



These Independent observations of nitrates in soils were a 

 prelude to Investigations of residual soil nitrogen initi- 

 ated by the Department of Water Resources. Soil profiles 



69 



