SECTION V 

 RESULTS AND DISCUSSION 



This section discusses the average nutrient concentrations 

 and discharges from tile drainage systems monitored. Empha- 

 sis is placed on long-term and short-term nutrient vsLrla- 

 bility, seasonal eind areal variability, and variability due 

 to agricultural practices, physiography, and soils. 

 Indigenous nitrogen in virgin soils, irrigated soils, and 

 parent materials is also discussed. 



Average Nutrient Concentrations 



The grand average concentration of nitrogen (nitrate- 

 nitrogen) in composited drainage discharged from all systems 

 intensively investigated throughout the entire period of 

 study was 19.3 mg/l . This concentration is very close to 

 the 21 mg/l value predicted in Bulletin No. 127 (l) by the 

 Department of Water Resources . 



Eighteen "satellite" systems, selected at random within the 

 major tiled areas, were monitored to obtain "back-up" data 

 and to determine the feasibility of monthly sampling. The 

 composited drainage (individual nitrogen concentrations 

 weighted by tile flow) averaged 23.6 mg/l for an eight -month 

 period . 



The composited drainage for all the tile systems monitored 

 reguleirly in the major tiled areas, the isolated stations 

 outside the areas, and the "satellite" stations averaged 

 20.0 mg/l nitrogen. 



The average concentration of phosphorus (orthophosphate) in 

 drainage composited from the intensively monitored major 

 tiled areas averaged 0.09 mg/l, slightly less than the 

 0.15 mg/l predicted in Bulletin No. 12?. 



Average Discharge 



Tile drainage discharge averaged 1.^ acre-feet per acre for 

 the same period of study; total dissolved solids (TDS) 

 averaged 3,625 mg/l. The 1959-63 values were excluded from 

 the grand average values given because the nutrient or TDS 

 constituents could not be weighted by flow. They are 

 presented in Table 7 for comparison. 



43 



