That depends on what's meant by the word "available". In general, the nitrates are the quickest acting or most "available" to plants, however different species of plants can uptake different forms. Usually though, complex nitrogen compounds must be broken down to simpler compounds before plants can uptake them. Also, different formulations (of fertilizers) can change the way a plant uptakes nutrients. Usually, the quickest acting is a water soluble fertilizer (a powder that dissolves readily in water). Then, there are granular fertilizers that work a bit slower, and finally there are slow-release types that take weeks to months to release.
Nitrite is the form of nitrogen that is most readily usable by plants Plants need nitrogen for the synthesis of the peptide bonds in proteins.
Nitrite/Nitrate Ions.
Nitrogen in the form of compounds
nitrates
it is the part of the nitrogen cycle
through roots from the soil
NO3
Plants that can use nitrogen from the atmosphere are known as nitrogen fixers. The legume or pea family of plants are famous for being able to do this.Most plants don't have this ability.
Most plants use single nitrogen atoms, not N2 molecules.
it is the part of the nitrogen cycle
through roots from the soil
This is because the particular form of nitrogen found in air โnitrogen gasโ cannot be assimilated by most organisms. For example, โNitrogen nutrients are water-soluble and as a result they are easily drained awayโ, so that they are no longer available for plants.
NO3
Because they don't want to.
Plants that can use nitrogen from the atmosphere are known as nitrogen fixers. The legume or pea family of plants are famous for being able to do this.Most plants don't have this ability.
Plants can get nitrogen from some of fertiliser
nitrogen
Most plants get nitrogen from fertilizers. Some plants can have a process called nitrogen fixing in which nitrogen from the is turned into ammonium compounds. Animals get their nitrogen from food, by eating plants and other animals.
Most plants use single nitrogen atoms, not N2 molecules.
Nitrogen is present as amino acids in plants which is an important factor for growth. It is formed when lightening strikes and a chemical reaction is produced and the nitrogen produced is adsorbed by the plants. Example of an amino acid - Nitrobactor.Nitrogen also occurs as the following in air:-Nitrogen oxideNitrous oxideNitrogen dioxideNitratesNitrogen is mixed with hydrogen to form ammonia which is a fertiliser.
Oxygen is needed by all organisms for respiration , carbon dioxide is needed by plants for photosynthesis , nitrogen is needed i form of nitrates by plants .