TABLE OP CONTENTS (Continued) 



Page 



Selection of Tile Drainage Systems 



for Monitoring 32 



Acreages Monitored 33 



Tile Monitoring Techniques 34 



Plow Measurement 34 



Nutrient Sampling 35 



Collection of Mineral Samples 36 



Collection of Dissolved Oxygen Samples 36 



Laboratory Techniques 36 



Nitrogen Determinations 37 



Phosphorous Determinations 38 



Electrical Conductivity 38 



Soil Extracts 38 



Collection of Agricultural Data 38 



Crops 38 



Irrigation 38 



Irrigation Runoff 39 



Pertllizatlon 39 



Historical Use of Pertilizers 39 



Types and Methods of Use 40 



Volatilization 40 



Data Sources 41 



Investigations of Native Nitrogen 41 



Soil Profile Nitrogen Sampling 4l 



Parent Material Nitrogen Sampling 4l 



SECTION V. RESULTS AND DISCUSSION 43 



Average Nutrient Concentrations 43 



Average Discharge 43 



Variability of Nutrient Concentrations and 



Tile Discharge with Time 44 



Long-term Nitrogen Variability 44 



Composited Drainage 44 



Individual Systems 45 



ix 



