Contamination of water and soil are the biggest concerns while using fertilizers.
Let’s first talk about manure storage.
Improper storage of manure can result in water pollution. The nutrient content of the manure, as well as the ability to spread it uniformly, are reduced with rainfall. Stockpiling solid manure uncovered and exposed to rainfall results in a reduction in the mineral and nutrient content. Also, the manure becomes sticky and difficult to spread uniformly. Leaching and run-off from the stockpiled manure may pollute ground and surface water.
Excessive Algal growth due to phosphorus run-off into a pond. Click here for a larger photo.
Risks to soil quality-
Improper manure and fertilizer management can adversely affect soil quality in the following ways:
Livestock manure can be a rich source of soluble ions like sodium (Na+) and potassium (K+) because animals retain only a small amount of the salt they consume. Repeat applications of manure at rates exceeding agronomic requirements can contribute to saline soil conditions. Long-term buildup of Na can also have a negative impact on soil structure by reducing soil particle aggregation.
Frequent traveling by loaded application equipment on wet soils can lead to soil compaction. Soil particles are squeezed together by compaction, reducing pore spaces available for air and water storage. This can inhibit root growth and increase surface runoff.
Risks to Water Quality-
When manure or fertilizer is improperly handled or applied at rates exceeding crop requirements, contaminants including nutrients and pathogens can enter
surface water and groundwater.
Groundwater is an important source of water for many rural communities. Manure and fertilizer application pose several risks to groundwater including contamination
from N, P, and pathogens. Manure and nitrogen fertilizer applications raise soil nitrate (NO3-) levels. Nitrate can leach into groundwater because it is soluble and mobile
in soils. High-risk groups (e.g., infants and pregnant women) who consume water high in NO3- (i.e., above 10 ppm N or 45 ppm NO3-N) have a reduced ability to transport oxygen in their bloodstreams. This condition is referred to as methemoglobinemia (“blue baby
syndrome”). Most soils across the US have a strong ability to adsorb (bind) P, which limits its entry into groundwater. However, leaching can occur when the soil’s adsorption capacity is saturated with high levels of P. This can happen from over-application of manure, particularly on coarse textured soils in high-rainfall or irrigated areas.
Transmission of manure pathogens to groundwater is rare, but can occur on coarse textured soils with high water tables. It can also happen when contaminated runoff enters groundwater through an improperly installed or poorly maintained well.
Agricultural runoff contaminated with nutrients and pathogens is the primary risk to surface water quality. Eutrophication is the enrichment of surface water bodies by nutrients, particularly N and P. Phosphorus is often the first limiting nutrient in surface water ecosystems. Excess P entering surface water from runoff or P contaminated
groundwater can result in increased algae production. Large algae blooms can significantly deplete oxygen levels when they die and decompose. Oxygen depletion will negatively affect aquatic animals. Blooms of bluegreen algae (cyanobacteria) can also release toxins that are harmful to aquatic life, livestock and wildlife if they ingest the water. Eutrophication is a natural occurrence that is accelerated by human activities.
Transmission of manure pathogens to surface water is more likely than groundwater contamination. Surface water contamination by manure pathogens can occur on fine textured soils prone to erosion, or in situations where manure is applied or deposited too close to surface water bodies. For example, livestock that have direct access to water bodies can pose a significant risk to surface water quality.
Risks to Air Quality
Manure and fertilizer application can also adversely affect air quality. For example, ammonium (NH4+) in manure or fertilizer converted to ammonia (NH3)
gas can be lost to the atmosphere. This is a particular concern with unincorporated surface applications of manure or urea (46-0-0). Ammonia losses are reduced with subsurface applications and when surface applied products are thoroughly incorporated.
Odor emissions are a risk when surface applied products are not incorporated.
Now that we understand the risks, how do farmers limit or control the risks?
Soil sample testing is one of the first key factors in controlling contamination issues. By knowing what the soil holds for minerals and nutrients, we can adjust the rate of application that is good for the soil for plant health. Soil sampling is just one factor in proper manure management. Planning ahead and knowing what crop(s) are being planted on that soil is also key. Corn takes a different level of nutrient uptake for growth than a grass like Alfalfa does. Knowing what nutrients each field is going to up-take assists in the planning of manure application.
Now that we know what plants are going to be grown and what nutrients are available within the soil, the next factor is how the manure fertilizer will be applied to the fields and what the environmental elements are. Top coating the fields increases the chances for run off, especially on soils that are already heavily water saturated. Injection of manure under the surface will reduce those risks but not completely eliminate them. The environmental elements that come into play are rain fall, snow depth, temperatures, air currents and even the grade (topography) of the land itself. The soil type and composition also have factors within the element.
As you can tell, manure management and application is an area that requires planning, patience and a strict rule of thumb. Many farms within my region utilize organizations like DairyOne, FSA and the NRCS to ensure they are doing the right applications. Most of the farms I know also have a manure management plan into affect. Those manure management plans are the planning tool where all of the manure, soil and water samples are combined with a planting schedule to determine when and where the manure fertilization is used and how much is applied to each differing field.
I hope this helps answer some concerns and questions. If you still have additional, please feel free to leave a comment or contact your local Soil and Water Conservation Office.