of suction devices (porous cups) installed at 1-foot 

 increments up to ^ feet in depth at several locations within 

 the tiled fields. The data show average nitrogen concentra- 

 tions in the field moisture between 1 and H feet compared to 

 the average concentrations observed during the same year for 

 each tile system (Table 25). Field moisture samples from 

 the surface (0 to 1 foot) contained much higher nitrogen 

 concentrations than did the subsurface and subsoil samples. 

 These high values were presumed to be influenced from ferti- 

 lizers and were not included in the averages. 



TABLE 25 



NITROGEN CONCENTRATIONS IN FIELD MOISTURE 

 AND DRAINAGE FROM FOUR TILED FIELDS 



1967 



Field 

 Code 



Soil 

 Series 



Soil 

 Type 



NO3-N : 



Im/ll'. 



Average NO^-N 

 (nig/1) 



Profile: Field : Tile . 

 Rangei/; Moisture—'^ ;Drainagel^ 



BFS 8003 Oxalis Sllty clay 17 - 39 25 



FBH 5056 Panoche Silty clay I8 - 53 33 



DPS 1016 Panoche Loam 16 -284 9^ 



FBH 4045 Panoche Fine sandy 36 - 64 48 



loam 



6 



37 

 28 



19 



1/ Range of concentrations by depth within the field. 

 "2/ Samples were extracted from porous cup devices within 



the fields. 

 3/ Weighted average concentrations. 



Prom the data presented in the two foregoing tables, very 

 little correlation seems to exist between the nitrogen 

 concentrations in soil moisture collected from the field and 

 that observed in tile drainage. 



Nitrogen in saturation extracts of different irrigated soils 

 (Table 21) is compared to that observed in tile drainage 

 (1967-68 averages) from the same-named soil series (Table 26) 

 A close correlation was found in only one out of six soil 

 series examined. This was for the Panoche series where there 

 was a sufficient number of samples represented in each case. 



78 



