Why are nitrites and nitrates added to soil

Algaecides can be expensive, and they also do not correct the source of the problem: the excess nitrogen or other nutrients that caused the algae bloom in the first place! Another potential solution is called bioremediation , which is the process of purposefully changing the food web in an aquatic ecosystem to reduce or control the amount of phytoplankton.

For example, water managers can introduce organisms that eat phytoplankton, and these organisms can help reduce the amounts of phytoplankton, by eating them!

The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and non-living things: the atmosphere, soil, water, plants, animals and bacteria. In order to move through the different parts of the cycle, nitrogen must change forms. In the atmosphere, nitrogen exists as a gas N 2 , but in the soils it exists as nitrogen oxide, NO, and nitrogen dioxide, NO 2 , and when used as a fertilizer, can be found in other forms, such as ammonia, NH 3 , which can be processed even further into a different fertilizer, ammonium nitrate, or NH 4 NO 3.

There are five stages in the nitrogen cycle, and we will now discuss each of them in turn: fixation or volatilization, mineralization, nitrification, immobilization, and denitrification. In this image, microbes in the soil turn nitrogen gas N 2 into what is called volatile ammonia NH 3 , so the fixation process is called volatilization.

Leaching is where certain forms of nitrogen such as nitrate, or NO 3 becomes dissolved in water and leaks out of the soil, potentially polluting waterways.

In this stage, nitrogen moves from the atmosphere into the soil. To be used by plants, the N 2 must be transformed through a process called nitrogen fixation. Fixation converts nitrogen in the atmosphere into forms that plants can absorb through their root systems. A small amount of nitrogen can be fixed when lightning provides the energy needed for N 2 to react with oxygen, producing nitrogen oxide, NO, and nitrogen dioxide, NO 2.

These forms of nitrogen then enter soils through rain or snow. Nitrogen can also be fixed through the industrial process that creates fertilizer. This form of fixing occurs under high heat and pressure, during which atmospheric nitrogen and hydrogen are combined to form ammonia NH 3 , which may then be processed further, to produce ammonium nitrate NH 4 NO 3 , a form of nitrogen that can be added to soils and used by plants.

Most nitrogen fixation occurs naturally, in the soil, by bacteria. In Figure 3 above , you can see nitrogen fixation and exchange of form occurring in the soil. Some bacteria attach to plant roots and have a symbiotic beneficial for both the plant and the bacteria relationship with the plant [ 6 ].

The bacteria get energy through photosynthesis and, in return, they fix nitrogen into a form the plant needs. The fixed nitrogen is then carried to other parts of the plant and is used to form plant tissues, so the plant can grow. Other bacteria live freely in soils or water and can fix nitrogen without this symbiotic relationship. These bacteria can also create forms of nitrogen that can be used by organisms. This stage takes place in the soil.

Nitrogen moves from organic materials, such as manure or plant materials to an inorganic form of nitrogen that plants can use. This becomes important in the second stage of the nitrogen cycle.

Mineralization happens when microbes act on organic material, such as animal manure or decomposing plant or animal material and begin to convert it to a form of nitrogen that can be used by plants. Several organic compounds compounds containing carbon compose the organic fraction of nitrogen in soil.

Soil organic matter exists as decomposing plant and animal residues, relatively stable products of decomposition-resistant compounds and humus. Nitrogen has accumulated in these various organic fractions during soil development. Organic matter formation and stability is largely related to long-term moisture and temperature trends.

With higher average temperatures, soil organic matter decreases. As moisture increases, soil organic matter increases. Higher temperatures lead to more rapid and complete organic matter decomposition to soluble products which can leach from soil.

Increasing moisture causes more plant growth, resulting in more organic residue as you move south and east in the Great Plains Figure 1. Through thousands of years of development, soils in the Midwest have accumulated significant quantities of organic matter. Yet, organic matter levels have declined due to the cultivation of virgin soils. This has increased organic matter oxidation and decreased soil organic matter nitrogen for crop uptake Figure 5. Soils that once contained 4 to 5 percent organic matter may contain only 1 to 2 percent after 50 years of cultivation.

However, soils under cultivation in the Midwest have, for the most part, reached a new equilibrium of organic matter levels with widespread commercial fertilizer use.

Reduced tillage techniques in combination with legume rotations and judicious fertilizer use may help maintain or slightly increase organic matter levels with time. Figure 5. The influence of tillage on organic nitrogen in soils in the Midwest. Ammonium exists in exchangeable and nonexchangeable forms. Nitrite NO 2 and nitrous oxide N 2 O are present in soil in lesser quantities. Plants normally use nitrogen in only the ammonium and nitrate forms.

Nitrite is actually toxic to plants. The nitrogen cycle Figure 5. The nitrogen cycle, as typically described, begins with nitrogen in its simplest stable form, dinitrogen N 2 , and follows it through the processes of fixation, mineralization, nitrification , leaching, plant assimilation, ammonia volatilization , denitrification , and immobilization. As described earlier, fixation is the process of converting dinitrogen gas to chemically reactive forms — where nitrogen combines with other elements such as oxygen, hydrogen, and carbon.

These forms are dependent on fixation. Lightning fixes nitrogen into various oxides that rain and snow deposit. Typically, this is less than 10 pounds of total nitrogen per acre per year. Bacteria can convert nitrogen to organic forms through fixation. Fixation can occur either in free-living organisms or symbiotically in association with legumes. Crop plants will take in the nitrate and use it to make proteins for growth.

One year the farmer will grow one of these crops and then the following years, the farmer will plant another crop in the nitrate rich soil. Growing different crops each year in a cycle is called crop rotation. Natural fertilisers such as manure or compost are used by farmers to provide a source of nitrate to increase crop yield.

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If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate. Advanced search. Skip to main content Thank you for visiting nature. Download PDF. Abstract IT is generally believed that nitrite is an intermediate product in the conversion of ammonium to nitrate in the soil where the conversion of nitrite to nitrate is important since relatively small quantities may have toxic effects on plant growth.