Nitrogen (N) - Understanding Minerals in your Soil

Posted by Neil Miles on

Nitrogen (N) – The unstable essential

Nitrogen is the most abundant mineral found in the plant, so there will be an inevitable price to pay if this mineral is not managed effectively.

Key Roles

This is the main mineral found in the green pigment, chlorophyll, so it is absolutely essential for photosynthesis, the most important of plant processes. Nitrogen is also the basis for plant amino acid production, so it has a major impact on plant growth and vitality. These nitrogen-based, protein building blocks are both structural and functional. Enzymes, for example, are proteins and therefore nitrogen dependant. They drive every biochemical reaction upon which all life is based. Nitrogen is also a major component of DNA and RNA, the genetic material that allows cells (and eventually, plants) to grow and reproduce.

There are no surprises that we have become enamoured with this particular input, because it is hugely important. The problem is that the sources of, requirements for, and application timing for nitrogen are often misunderstood. As a result of this confusion, nitrogen has become the most misused and abused of all minerals.

Key Characteristics

Nitrogen can cycle between the soil, the plant and the atmosphere (just like carbon). The air we breathe contains almost 79% nitrogen and we were supposed to source significant amounts of this "free gift" from the atmosphere, via nitrogen-fixing organisms. Nitrogen is also stored and released by humus in the soil and, as crop residues decompose, some of their protein reverts to plant-available nitrogen. The fertiliser from the bag actually accounts for much less than half of the nitrogen used to produce your crop, so it is so important to manage the nitrogen cycle efficiently.

When we talk composting strategies, we strive to build a layer cake based upon carbon and nitrogen. The green layer (nitrogen) is based on the nitrogen-dominant chlorophyll. The alternating brown layer (carbon) involves organic matter, where nitrogen has departed and returned to the atmosphere as nitrogen gas.

Ideal Levels

There are two forms of nitrogen in your soil – ammonium nitrogen and nitrate nitrogen. Ideally, we like to see equal amounts of each (a 1:1 ratio). The maximum soil requirement for each form of nitrogen is 20 ppm. However, plants can thrive with less than this.

The ideal ratio between these two forms of nitrogen is different in the plant, when compared to the soil. In the leaf, we are seeking three parts of ammonium nitrogen to one part nitrate nitrogen (a 3:1 ratio). This different ratio in the leaf is partially related to an inflow of ammonium nitrogen from the atmosphere, directly into the leaf, via nitrogen-fixing organisms living on the leaf surface. Nitrogen-fixing organisms in the soil also constantly boost the ammonium component within the plant. This key 3:1 ratio between ammonium and nitrate nitrogen in the plant is a really important, but often unrecognised, player in plant health and resilience. Mismanagement of this ratio is tragically common. In fact, this ratio is often inverted and, when this happens, the season is set to be dominated by stress and strife. This nitrate excess is a calling card for insects and disease and the battle begins, as every pest arrives to party.

Key Considerations

Nitrogen fixation is dependent on a trace mineral called molybdenum, which is lacking in many soils. Cobalt is also important to ensure access to the atmospheric bounty. The third component of successful conversion of nitrogen gas from the atmosphere to ammonium nitrogen in the soil is an ongoing supply of soluble phosphorus to enable the creation of ATP (adenosine tri-phosphate), which fires the nitrogenase enzyme. This is the enzyme that allows the harvest of atmospheric nitrogen.

The best way to ensure a constant trickle feed of soluble phosphate for this purpose is to ensure that your soil contains beneficial fungi. These creatures are missing in many soils, but they exude acids that break the bond between locked-up calcium and phosphorus and deliver both minerals into soil solution. All cellulose-digesting fungi offer this benefit (along with humus creation), but the most important of these organisms is mycorrhizal fungi. These key organisms are missing in 90% of our soils, but the good news is that these creatures can be successfully re-introduced for as little as $20 per hectare Nutri-Life from NTS, available for purchase from us direct.

While it is always important to ensure sufficient nitrogen supply for maximum yield, it is also critically important that we do not assume that, if a little works well, then more will work better. Nitrogen is the mineral most often abused in terms of this ‘more-on' approach. Excess nitrogen can reduce resilience and lead to reduced uptake of minerals like potassium, calcium and boron.

One important strategy to maximise response (in the right form) while minimising N inputs, involves the foliar application of urea. The vast majority of soil-applied urea ends up as nitrate nitrogen in the plant. Now, there is a hugely energy-intensive process involved to convert nitrate nitrogen in the leaf into protein. This can suck up 17% of the plants photosynthates, which could have been used much more effectively, including the boosting of your bank account via increased yield at season's end.

The conversion of nitrate N to protein involves three steps – nitrates to amines, amines to amino acids, and then amino acids to protein. The energy-sucking stage of this three-step process is the conversion of nitrates into amines. The irony here is that urea is an amine. The foliar route into the plant is at least 12 times more efficient, so we can use much less urea when it is applied as a foliar. However, the key consideration here is that we are supplying an amine, which is easily converted to amino acids and then proteins. We have effectively avoided the nitrate-based energy drawdown and used much less N in the process. Urea can be very successfully foliar applied at rates of 8 – 20 kg per hectare, but it should always be combined with humic acid to buffer the N and magnify the nitrogen uptake. 

Originally published, with thanks, as part of an article from Nutri-Tech Solutions.

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