Findings Show Synthetic Nitrogen Fertilizers Leach From Soil to Groundwater Much Faster Than Previously Thought
While nitrate is a common nitrogenous compound due to natural processes of the nitrogen cycle, anthropogenic sources have greatly increased the nitrate concentration, particularly in groundwater. Scientists in France and at the University of Calgary say that nitrogen fertilizer applied to crops lingers in the soil and for decades leaches toward groundwater -much longer than previously thought. The study, Long-term fate of nitrate fertilizer in agricultural soils, was published in the Proceeding of the National Academy of Sciences (PNAS) in October.
Nitrate is a problem as a contaminant in drinking water (primarily from groundwater and wells) due to its harmful biological effects. High concentrations can cause methemoglobinemia, and have been cited as a risk factor in developing gastric an intestinal cancer. Due to these heath risks, a great deal of emphasis has been placed on finding effective treatment processes to reduce nitrate concentrations to safe levels.
An even more important facet to reduce the problem are prevention measures to stop the leaching of nitrate from the soil which has been found to be much more serious than previously thought. Some suggest that reducing the amount of fertilizers used in agriculture will help alleviate the problem, and may not hurt crop yields.
In water, nitrate has no taste or scent and can only be detected through a chemical test. In babies, especially those under six months old, methaemoglobinaemia , commonly called “blue-baby syndrome,” can result from oxygen deprivation caused by drinking water high in nitrate. Methemoglobin is probably formed in the intestinal tract of an infant when bacteria converts the nitrate ion to nitrite ion. Because of the oxygen deprivation, the infant will often take on a blue or purple tinge in the lips and extremities, hence the name, blue baby syndrome.
Other studies claim that intake of nitrate contaminated groundwater is linked to birth defects, hypertension and high blood pressure in adults.
The study in PNAS shows that the loss of synthetic nitrogen (N) fertilizer in groundwater occurs at low rates over many decades, which means it could take years to reduce nitrate contamination in groundwater, including in aquifers that supply drinking water. The researchers recommend that as a result of the “legacies of past applications of synthetic fertilizers in agricultural systems,” mitigation or restoration measures must take into account this delay.
In fact, the scientists found that three decades after application of isotopically labeled fertilizer N to agricultural soils in 1982 12-15% of the fertilizer-derived N is still residing in the soil organic matter, while 8-12% of the fertilizer N had already leached toward the groundwater. The scientists estimate that it will continue to leach in low amounts for at least another 50 years, much longer than previously thought.
Although there are many sources of nitrogen (both natural and anthropogenic) that could potentially lead to the pollution of the groundwater with nitrates, the anthropogenic sources are really the ones that most often cause the amount of nitrate to rise to a dangerous level. Waste materials are one of the anthropogenic sources of nitrate contamination of groundwater. Many local sources of potential nitrate contamination of groundwater exist such as, “sites used for disposal of human and animal sewage; industrial wastes related to food processing, munitions, and some polyresin facilities
“There’s a lot of fertilizer nitrogen that has accumulated in agricultural soils over the last few decades which will continue to leak as nitrate towards groundwater,” Dr. Mayer says.
High rates of fertilizer application may also increase the natural nitrate levels found in certain vegetables, such as lettuce and root crops. Research has indicated that long-term exposure to nitrates through food and water may increase risk of thyroid disease. In the body, nitrate competes with uptake of iodide by the thyroid, thus potentially affecting thyroid function.
Organic farming and land management uses natural, less soluble sources of nitrogen, phosphorous and magnesium, including cover crops, compost, manure and mineralized rock, in order to promote increases in soil organic matter and a healthy soil structure.
The most important step for farmers is to reduce the amount of nitrogen applied to the crops. This is easier said than done because most farmers consider nitrogen fertilizer to be “cheap insurance” against a crop failure. From a financial standpoint, a farmer would rather add too much nitrogen to his crop than too little.
Farmers must be very cautious about adding nitrogen during periods in which the ground is not yet frozen but the grass is not growing. Another key is avoiding over-irrigation, which increases the chance of nitrate leaching while doing nothing for the plant. Effort should also be made to reduce the amount of nitrogen applied to older sites and collect drainage water instead of allowing it to drain into a river or stream. Zeolite amendments should also be incorporated where necessary. Zeolite is a mineral with a high cation exchange capacity that can hold on to things like potassium, calcium, phosphorous, magnesium or ammonium.
About the Author
Mason Grant is a Doctor of Acupuncture, trained Naturopathic Physician, avid gardener and has practiced holistic medicine and healing for more than twenty years. In his free time he is a writer, independent researcher and investigative journalist.
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