Fertilizer Management

Fertilizers are generally defined as "any material, organic or inorganic, natural or synthetic, which supplies one or more of the chemical elements required for the plant growth". Most fertilizers that are commonly used in agriculture contain the three basic plant nutrients: nitrogen, phosphorus, and potassium. Some fertilizers also contain certain "micrnutrients," such as zinc and other metals, that are necessary for plant growth. Fertilizers are applied to replace the essential nutrients for plant growth to the soil after they have been depleted.

Excess amounts of fertilizers may enter streams creating sources of nonpoint pollution. Fertilizers most commonly enter water sources by surface runoff and leaching from agricultural lands. Large amounts of nitrogen and phosphorous are present in the runoff. Increased amounts of nitrogen, phosphorous, and other micronutrients can have negative impacts on public health and aquatic ecosystems.

Handling and Storing Fertilizer

  • Follow label directions
  • Lock or otherwise secure storage container valves when not in use
  • Storage buildings should have impermeable floors (impermeable secondary containment dikes can be used)
  • DO NOT store fertilizer underground in containers or pits
  • Mix and load fertilizers at the application place when possible
  • Handle and store fertilizer away from wellheads and surface water
  • Immediately recover and reuse or properly dispose of fertilizer spills
  • Always store fertilizers in their original containers

Application of Fertilizer

Fertilizer application timing - Fertilizers with nitrogen present should be applied as closely as possible to the period of maximum crop uptake. Partial application of fertilizer in the spring with small additions as needed can reduce leaching and improve nitrogen uptake. Fertilizing in the fall has been shown to cause groundwater degradation.

Application Rates and Fertilizer Types - It is necessary to sample soil every year to determine crop nutrient needs for accurate fertilizer recommendations. To calculate the optimal rate of application other sources that contribute nitrogen and phosphorous to the soil should be considered. Previous crops, irrigation water, manure and organic matter can contribute nitrogen into the soil. Organic matter and manure contribute phosphorous. Crops can quickly take up nitrate forms of nitrogen, but are subject to leaching loss. Fertilizer with nitrogen should be limited when leaching potential is moderate to high. If the leaching potential is moderate to high, ammonium nitrogen fertilizers should be used because they are not subject to leach immediately. However, in warm moist conditions ammonium quickly turns into nitrate. More slowly available nitrogen fertilizers should be used in these situations. Although phosphorous is less prone to leach, loss through surface runoff is common so phosphorous should only be applied as needed and at recommended rates.

Fertilizer application equipment should be checked and calibrated annually. The most efficient application method for many crops is to place dry fertilizer in bands into the ground. Band or drilled row fertilizers can be recovered by the crop more efficiently because of their close proximity to the seed. Surface-applied fertilizers should be mechanically incorporated into the soil to reduce losses through surface runoff. Fertilizer should never be applied when the ground is frozen. Fertilizer application should be limited on slopes and areas with high runoff.

Irrigated crop production has the highest potential for water contamination because of the large quantity of water that is applied. When excess water is applied nitrogen and phosphorous can leach into groundwater or runoff into surface water. Using systems such as sprinklers, low energy precision applications, surges and drips help producers apply water efficiently and uniformly. Delivery systems such as lined ditches and gated pipes as well as reuse systems such as field drainage recovery ponds are efficient.

Why is it important to manage fertilizer use?

Environment
Nitrogen and phosphorous occur naturally in streams throughout Utah and are important nutrients to aquatic ecosystems. However, too much of these nutrients can cause serious problems in lakes and streams. Often times in agricultural areas, excess nitrogen enters the system from animal operations or from irrigation return flow. These added nutrients may lead to fish kills, noxious aquatic plant growth, and foul odors.

Human Health
Nitrogen fertilizer (organic and inorganic) can contribute to nitrates in drinking water. Pregnant or nursing women and infants are especially vulnerable to nitrate related health problems. Nitrate can interfere with the ability of blood to carry oxygen in infants 6 months old or under. This is known as "blue baby syndrome". Infants may experience shortness of breath. Infants that receive formula mixed with well water with a high nitrate concentration level may have an increased risk of getting this syndrome. People over 6 years of age are not usually at risk for this syndrome because their digestive systems naturally absorb and excrete nitrates. 

Little is known about the long term effects of drinking water with elevated levels of nitrates. However, there has been some research suggesting that nitrates may play a role in spontaneous miscarriages. Also, water sources that show nitrate contamination have the potential for other contaminants like bacteria and pesticides to reach groundwater along with nitrates.

To test your water for nitrates you may purchase a kit at your local hardware store for approximately $10-20. You may use the following table to help you interpret your results. For more information about nitrates, click here.

Additional Information