Managing Nitrogen to Protect Water Quality

Excess nitrogen not used by growing crops coverts to nitrate (NO3-), which can be very mobile in soils. Nitrate can leach through the root zone and contaminate shallow groundwater. Areas with coarse or sandy soils are at greater risk for nitrate leaching to groundwater. Nitrogen can also be carried in runoff and can contaminate surface waters.

Nitrogen must be managed properly to increase crop yields and protect water quality. Manure is a valuable source of nitrogen on the farm; however, nitrogen from manure and chemical fertilizers can pollute both surface and groundwater.

Nitrogen

Nitrogen exists in organic and inorganic forms. Inorganic nitrogen like nitrate (NO3-) and ammonium (NH4+) can be immediately taken up by growing crops. Organic nitrogen must be mineralized or changed into these inorganic forms before it can be used by growing plants.

Excess nitrogen in aquatic ecosystems can be harmful. When there is a sufficient supply of phosphorus available in aquatic ecosystems, high concentrations of nitrogen can promote the growth of aquatic plants and algae. When algal blooms die and start to decompose, dissolved oxygen is depleted in the water. The lack of dissolved oxygen can suffocate aquatic organisms like fish resulting in fish kills.

Algal blooms can also affect the aesthetics of a water body, producing large algal scums, as well as impair recreational uses like swimming and boating. Under certain conditions (pH and temperature), high ammonium levels in surface waters can be toxic to fish.

High nitrate-nitrogen levels in drinking water can harm human and livestock health. High nitrate levels in drinking water can impair the blood’s oxygen-carrying capacity in small infants causing “blue baby syndrome.” Similarly, extremely high nitrate levels can be toxic to ruminant animals like cattle and sheep.

Nitrate-nitrogen levels greater than 10 milligrams per litre are above drinking water quality guidelines for humans. Levels greater than 100 milligrams per litre are above livestock watering guidelines.

Protect Water Resources

Managing nitrogen in the right way will ensure clean drinking water and healthy aquatic systems.

• Test soil and manure for nutrient content. Routinely test soil and manure for nitrogen, phosphorus and potassium content. Apply only enough fertilizer or manure to meet crop nutrient requirements. Ensure that an adequate land base is available for spreading manure at appropriate rates.
• Reduce the number of acres in summerfallow. Reduce cultivated summerfallowing to prevent soil erosion and reduce the amount of nutrients and sediment transported in runoff to surface waters.
• Ensure sufficient lagoon and manure storage. Liquid manure lagoons must be properly sealed with compacted clay or plastic liners to prevent nitrogen leaching to shallow groundwater. Manure, if stockpiled, must be contained on compacted soil or concrete pads to prevent leaching to groundwater. All runoff from manure stockpiles must be contained to prevent contamination of surface waters.
• Do not apply manure on land with high risk runoff. Applying manure or fertilizers on frozen, snow-covered, saturated or heavily compacted bare soils increases the risk of contaminated runoff reaching surface water.
• Maintain healthy riparian areas. Riparian areas are zones of vegetation alongside streams and around water bodies. By feeding livestock away from creeks and controlling their access to riparian areas through rotational grazing, alternate watering sources and fencing, the risk of manure reaching surface water decreases.
• Test groundwater wells. Ensure appropriate tests are done for levels of nitrate and bacteria every year on groundwater wells.