Over 90 percent of the drinking water consumed in Idaho is supplied by groundwater. Nitrate is the most common groundwater pollutant in Idaho and in the United States. Nitrates in groundwater can originate from many sources, including agriculture, septic tanks, landfills, lawns and gardens, industry and municipalities. Nitrogen is an element essential for all plant and animal life.
Agriculture affects both nitrogen additions and subtractions to the soil.
Additions include nitrogen fertilizers, crop residues, nitrogen fixation by legumes, and manures. The nitrogen cycle. In rural areas of Idaho, potentially significant sources of nitrogen for groundwater contamination include nitrogen fertilizers, private septic systems, livestock feedlots, barnyards, and legumes used as green manures. Soil sampling should be done 3 to 4 weeks before planting a crop. The soil samples should be representative of the field.