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Water and Air Quality

Water is the lifeblood of Idaho. More than 22 million gallons of water are used in the state each day. More than 97% of this water irrigates 4.1 million acres of farmland. Eighty percent of this water comes from surface sources (rivers and reservoirs); the other 20% is groundwater. Agricultural best management practices (BMPs) to protect water is very important.

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.

Phosphorus is a common water pollutant in Idaho's lakes and rivers. Phosphorus originates from many sources, including agriculture.

Currently, the quality of water used in Idaho is very good compared with water in other areas of the United States and the world.

Nitrogen is an element essential for all plant and animal life. The interlocking succession of nitrogen reactions occurring in the soil is known as the nitrogen cycle. Agriculture affects both nitrogen additions and subtractions to the soil. Additions include nitrogen fertilizers, crop residues, nitrogen fixation by legumes, and manures. Subtractions attributed to agriculture include crop removal (harvesting), plant uptake and nitrogen leaching.

Federal and state standards dictate that drinking water should not contain more than 10 parts per million (ppm) NO3-N. 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.

Specific types of BMPs for nitrogen fertilizer management that should be employed in many areas of Idaho include:

  • Soil sampling
  • Fertilizer recommendations based on research
  • Timing of fertilizer application
  • Fertilizer placement
  • Nutrient credits for legumes and manures
  • Nitrification inhibitors
  • Manure management
  • Irrigation systems management
  • Slow-release nitrogen fertilizers
  • Crop rotation selection
  • Variable fertilizer management


Phosphorus is essential to all forms of terrestrial life. It is widely distributed over the surface of the earth in biologically available forms, cycling within plants, animals, soil and water in the phosphorus cycle. In commercial agriculture, fertilizer is the major phosphorus addition to this cycle.

Water quality problems associated with phosphorus are generally confined to surface waters. Phosphorus in soil is tightly held to soil particles, is immobile, and does not leach. Consequently, contamination of groundwater is rarely a problem.

Many human activities contribute phosphorus to surface waters. Agricultural land enriched with phosphorus by fertilization or manure can contribute substantial amounts of phosphorus to surface waters as the result of runoff and/or erosional processes. Activities associated with modern agriculture often significantly increase soil erosion and water runoff from land and transport sediment into surface waters.

Surface water pollution with phosphorus is controllable — by reducing soil erosion and keeping soil out of creeks, streams, rivers and lakes.

Specific BMPs for phosphorus fertilizer and manure management that should be employed to protect surface water quality in many areas of Idaho include:

  • Soil erosion control
  • Fertilizer recommendations based on research and soil sampling
  • Correct phosphorus fertilizer placement
  • Variable fertilizer management
  • Efficient manure management
  • Barnyard and/or feedlot runoff control
  • Conservation tillage and reside management
  • Buffer (filter) strips


Air quality issues associated with animal operations include gas (odorous gases, greenhouse gases -GHGs), odor, VOC and particulate matter-PM (PM2.5, PM10 and total suspended particulates-TSP) emissions from animal facilities. While some odorous compounds can cause health problems, odors from livestock are mainly a community or individual perception issue. Many different compounds can be the potential cause of odors from animal operations. These compounds can generally be classified as VOCs, odorous sulfur compounds and ammonia. PM can be emitted directly (i.e., dust) or formed in the atmosphere by the chemical reaction of pollutants such as sulfur oxides, nitrogen oxides, VOCs and ammonia. The major GHGs associated with agricultural operations are carbon dioxide, methane and nitrous oxide.



Methane; Nitrous Oxide


University of Idaho Extension

Phone: 208-934-4417, (c) 208-539-2582