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Nitrogen

Functions of Nitrogen

In natural ecosystems, many processes, such as primary production and decomposition, are limited by the available supply of nitrogen. In other words, nitrogen is often the limiting nutrient, the nutrient that’s in shortest supply and thus limits the growth of plants and other organisms.

Nitrogen forms 16% if all plant proteins and it is a vital component in chloroplasts – the factories that synthesize energy from sunlight.

Nitrogen forms the basis of amino acids and proteins in plants and it is an important constituent of DNA, RNA and enzymes.

Nitrogen Management

As Nitrogen is critical for plant growth, farmers have traditionally actively applied industrial Nitrogen fertilizers. In same cases that has led to excess of Nitrogen. Excessive accumulation of Nitrogen in plants hinders Calcium and Potassium intake and may cause problems for human health and environment.

High levels of atmospheric nitrogen are associated with production of acid rain in the form of nitric acid HNO3 and contributions to the greenhouse effect as a nitrous oxide N2O. Nitrogen comprises the smallest percentage of the three green house gases but it is 310 times more potent than CO2.

Farmers can save costs by tapping into Nitrogen that is in the atmosphere. There is 74 000 tons of Nitrogen in a gas form above every hectare.

Symptoms of Nitrogen deficiency in plants

Symptoms of excessive Nitrogen in plants

Yellowing older foliage Potassium and Calcium are deficient
Reduced plant/leaf size Extremely dark green leaves
Fewer stems “Burning” of leaf tips, causing them to turn brown
Dwarfed plant growth Some leaves turning yellow, due to abundance of nitrogen but lack of other nutrients
Thin and upright habit
Reduced tillering

Tapping in to free atmospheric Nitrogen

In a symbiotic relationship with the soil bacteria known as ‘rhizobia’, legumes form nodules on their roots (or stems, see figure below) to ‘fix’ nitrogen into a form usable by plants (and animals).

Plants cannot fix nitrogen on their own, but need it in one form or another to make amino acids and proteins. Because legumes form nodules with rhizobia, they have high levels of nitrogen available to them.

Their abundance of nitrogen is beneficial not only to the legumes themselves, but also to the plants around them. There are other sources of nitrogen in the soil, but are not always provided at the levels required by plants, making the symbiotic relationship between legumes and rhizobia highly beneficial.

By setting up correct conditions, you can optimize natural Nitrogen fixation.

Ways to promote natural fixation of Nitrogen

A good calcium/magnesium ratio
An adequate supply of soluble phosphate (ATP)
Soluble iron (humic acid)
Molybdenum (part of the nitrogenase enzyme).
Adequate Cobalt

Access to fixed or available forms of nitrogen limits the productivity of crop plants and thus food production. Nitrogenous fertilizer production currently represents a significant expense for the efficient growth of various crops in the developed world.

Promoting symbiotic fixation of Nitrogen can save costs in agriculture while reducing greenhouse gases in the atmosphere. There are important nitrogen-carbon links. The global increase in fixed nitrogen may be fertilizing the Earth, transferring significant amounts of carbon from the atmosphere to the biosphere, and mitigating global warming.

Biological nitrogen fixation is the conversion of atmospheric N2 to NH3, a form that can be used by plants.

Symbiotic nitrogen fixation is part of a mutualistic relationship in which plants provide a niche and fixed carbon to bacteria in exchange for fixed nitrogen.

Association between root-nodule bacteria and rhizobacteria in natural N fixation (Florence Mus et all, 2016)

Nitrogen as a chemical elemental

Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at about seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2.

Dinitrogen forms about 78% of Earth’s atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids (and thus proteins), in the nucleic acids (DNA and RNA) and in the energy transfer molecule adenosine triphosphate.