Environmental Concerns Associated with Fertilizer Use
Use of fertilizer materials has generated numerous environmental concerns in recent years. Concerns can be categorized by their effect on water quality, air quality, and human and animal health. In each case, constituents of primary interest are nitrogen and phosphorus, although others need to be considered depending on the fertilizer source. As previously covered, there are many available fertilizer sources including commercial fertilizers, biosolids and animal waste. Environmental concerns become a potential hazard with the misuse of these materials. Misuse generally arises when fertilizer application rates exceed agronomic ...view middle of the document...
The most common pathway for land applied nitrogen to reach surface waters is by runoff waters. These waters will often contain soluble materials and soil sediments. Therefore, even nitrogen applied at agronomic rates and incorporated into the soil is susceptible to moving into surface waters by runoff when carried by soil particles. Nitrate nitrogen is a soluble N form and ammonium nitrogen can be attached to the soil particles as they are carried into the stream or impoundment. To minimize nitrogen problems associated with runoff from fields into surface waters several steps can be taken. One of the most effective is to maintain plant residue on the soil surface which will enhance water infiltration and reduce the amount of soil sediments moved from the field into surface water. Another effective practice is to leave a buffer strip of vegetation between the field and the surface water, which can act as a trap for many of the soil sediments. By catching sediments in the buffer strip the amount of nitrogen reaching the surface water is reduced.
Although eutrophication of surface waters is important, much of the regulation in other states focuses on the use of nitrogen in areas where a subsurface aquifer is within 10 feet of the soil surface. Nitrogen in the NO3- form is very susceptible to leaching through the soil profile as previously discussed, therefore, these sites possess a real possibility for elevated levels of NO3- to enter the aquifer when nitrogen application rates are in excess of agronomic rates. Concerns with nitrate reaching an aquifer are generally related to animal and human health rather than an imbalance in environmental nutrient requirements.
Methemoglobinemia (blue-baby syndrome) can result from the ingestion of nitrate in water or nitrate-rich food products. Ingested nitrate can then be reduced to nitrite in the upper gastro-intestinal tract, and once incorporated in the blood system can form methemoglobin. Methemoglobin, unlike hemoglobin, cannot function as an oxygen carrier ultimately resulting in anoxia or suffocation if high amounts are present. Infants younger than 3 months are highly susceptible to gastric bacterial nitrate reduction because they have very little gastric acid production and low activity of the enzyme that reduces methemoglobin back to hemoglobin.
N-nitrosamines are potent carcinogens in animals. These compounds can be synthesized from amines and nitrous acid under certain conditions. When nitrate is reduced to nitrite it can give rise to the formation of N-nitrosamine compounds that are an important class of chemical carcinogens for humans. However, nitrosamines occur in very few foods and at very low levels because of their chemical instability. It is important to note that the presence of nitrosamines in food products is generally not associated with nitrates from N fertilizers, but rather the use of nitrite as a curing agent in meats, poultry, and fish. Potassium nitrate has...
