Nitrogen Cycle Animation Transcript

Essential nutrients | Toxicities and deficiencies | pH | Soil sampling | Nitrogen cycle

Scene one

The overall nitrogen cycle is displayed as a series of arrows including a cow, vegetation and roots, soil, a cloud of vapour, and a tractor dispensing fertiliser. This scene is accompanied with the text "Nitrogen (N) exists in different forms in the air, soil, water, and in living organisms. The soil is a major reservoir for N in an agricultural system. The N cycle is complex and involves many different soil micro-organisms and enzymes."

Scene two

The animation zooms to show the roots of the legume growing in the soil, and the Rhizobium nodules present on the roots. This scene is accompanied by the text "Nitrogen from the air (N₂) can be converted into ammonium (NH₄⁺) by bacteria (eg. Rhizobia species) that live in the nodules on the roots of legumes, or by other bacteria (eg. Azobacter species) that live freely in the soil. This process is known as nitrogen fixation."

Scene three

The animation shows the tractor applying nitrogen fertilisers to the soil, and the cow adding urea in the form of urine. This scene is accompanied by the text "Nitrogen fertilisers are usually applied as urea or ammonium compounds such as ammonium phosphate. Urea is converted to ammonia (NH₃) by urease enzymes in the soil and can then be converted to ammonium (NH₄⁺) by bacteria and other micro-organisms such as archaea and fungi.”

Scene four

Arrows demonstrate the transformation of nitrogen in this scene. This scene is accompanied by the text "Large amounts of ammonium (NH₄⁺) in the soil can form an aqueous ammonia (NH₃) that escapes to the air as ammonia gas. This process is called volatilisation.”

Scene five

This scene displays the components of the organic matter pool, and how decaying plant material and manure contribute to the organic matter pool. Organisms in the soil are shown to play an important role in transforming organic nitrogen into other forms for plant use. This scene is accompanied by the text "The soil organic matter pool contains decaying plant material and manure, which are food for the living organisms in the soil. Soil organisms such as bacteria and fungi turn nitrogen in the organic matter into ammonia (NH₃) and then into ammonium (NH₄⁺) and release it back into the soil. Some of the soil micro-organisms also take up the NH₄⁺ and immobilise it, releasing it back into the soil when the micro-organisms die."

Scene six

Two magnifying glasses appear on screen to demonstrate the nitrifying soil bacteria and archaea causing nitrification. This scene is accompanied by the text "Ammonium (NH₄⁺) may be converted into nitrite (NO₂^-) and then to nitrate (NO₃^-) by nitrifying soil bacteria and archaea. This process is known as nitrification. Nitrous oxide (N₂O) may be generated by nitrifying soil bacteria."

Scene seven

Arrows demonstrate plant roots taking up various forms of nitrogen in the soil, and a magnifying glass demonstrates the fixation of ammonium by clay in the soil. This scene is accompanied by the text "Both ammonium (NH₄⁺) and nitrate (NO₃^-) in the soil can be taken up by plant roots. NH₄⁺ can also be trapped by some clay minerals, this is called ammonium fixation. Fixed NH₄⁺ can only be slowly released for plants and micro-organisms to use."

Scene eight

Arrows demonstrate the transformation of nitrate through the organic matter pool via micro-organisms. This scene is accompanied by the text "Nitrate (NO₃^-) not taken up by plant roots can also be immobilised by soil micro-organisms. When these soil micro-organisms die and become part of the soil organic matter pool, the cycle of organic nitrogen to ammonia (NH₃) and then ammonium (NH₄⁺) continues."

Scene nine

Arrows simply show that leaching of nitrate below the root zone can occur if nitrate is not captured. This scene is accompanied by the text "Nitrate (NO₃^-) will be leached below the root zone if not captured by plants and soil micro-organisms. NO₃^- leaching contributes to soil acidification."

Scene ten

Rain enters the soil creating a waterlogged area of soil, thereby allowing denitrifying micro-organisms to convert nitrate to various gases that escape into the atmosphere as the soil dries. This scene is accompanied by the text "Denitrification typically occurs when there is little to no oxygen, as in a waterlogged soil. A diverse range of denitrifying micro-organisms progressively convert nitrate (NO₃^-) to nitrite (NO₂^-), to nitric oxide (NO), nitrous oxide (N₂O), and nitrogen gas (N₂). These gases can then escape into the atmosphere as the soil dries."

Scene eleven

The tractor drives off screen carting a bale of hay while the cow spontaneously disappears to signify the removal of animal products from the agricultural system. This scene is accompanied by the text "Nitrogen can also be removed from the agricultural system by harvest of plants and animal products (milk, wool, meat), by soil erosion, and in surface water runoff."

Scene twelve

The entire nitrogen cycle is displayed as a series of arrows as for Scene 1, however, the compounds of transformed nitrogen throughout the cycle are also displayed. This scene is accompanied by the text "The nitrogen cycle is complex and different parts of the cycle can be happening simultaneously. Transformations of nitrogen throughout the cycle can be continuous or sporadic, depending on soil and climatic conditions."

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