How Do Some Nitrates Get Removed From the Soil?

Nitrogen Cycle

• Nitrogen undergoes several chemical changes as it travels through soil. These chemical changes are part of the nitrogen cycle. Nitrogen enters soil through a variety of ways. Fertilizers, air, water and living organisms all contribute to soil's nitrogen content. Inorganic nitrogen compounds enter soil through the atmosphere. Nitrogen joins with rainwater and penetrates the soil. Inorganic nitrogen is readily available for plant uptake. Plant uptake accounts for some nitrogen loss. Organic nitrogen is not readily available for plant uptake. Soil bacteria takes in organic nitrogen and processes the nutrient. Bacteria successfully transforms organic nitrogen into nitrates and ammonium which are utilized by plants. Nitrogen returns to soil as plants decay. In this way the cycle is completed.

Nitrate Loss

• The nitrogen cycle is not a closed system. Although plants and rainwater return nitrogen to soil, some nitrogen is lost through drainage, plant production and microorganism digestion. Soil loses nitrates through a process called denitrification, which is caused when soil bacteria break down nitrogen. Nitrates are released back into the atmosphere. Volatilization occurs when urea-based fertilizers break down on soil surfaces, sending nitrates back into the atmosphere. Highly porous soils with low amounts of organic matter often drain so rapidly that nutrients are unavailable to both plants and soil-dwelling micoorganisms. When rainwater and nitrates drain quickly into soil they settle deep below the surface where they are unavailable to plants. In these circumstances the nitrates are essentially lost and removed from the topsoil.

Cautions

• Leaching is another way in which nitrates are removed from soil. When excess amounts of fertilizer and nitrates enter groundwater, streams and other bodies of water, nitrates are leached from the soil and carried into the water supply. Avoid over-fertilizing lawns and gardens. When excess nitrates enter water supplies they encourage algae development. Algae blooms are responsible for fish kills and water supply contamination.

Considerations

• To compensate for nitrate loss, many growers fertilize their soil annually. Before adding nitrogen to your soil, submit soil samples to a local university extension soil testing agency. Soil scientists will analyze your soil's content and structure and provide fertilizer recommendations that are customized for your specific crop and soil conditions. Another way to increase nitrogen in your soil is to amend it with compost and organic matter. If your soil is too high in nitrogen, stop applying fertilizer and compost. Microorganisms and rainwater will slowly remove excess nitrogen from your soil.