Nitrate (NO3-) versus ammonium (NH4+)

Soil nitrogen conversion processes


The three main sources of nitrogen, used in agriculture are urea, ammonium and nitrate. The biological oxidation of ammonia to nitrate is known as nitrification. This process consists of various steps, as demonstrated in Figure 1, and is mediated by autotrophic, obligately aerobic bacteria. In waterlogged soils the oxidation of NH4+ is thus restricted. Urea is decomposed by the enzyme urease or chemically hydrolyzed into ammonia and CO2. In the ammonification step, ammonia is converted by ammonium-oxidizing bacteria into ammonium. In a next step, ammonium is converted by nitrifying bacteria into nitrate (nitrification).

The nitrogen conversion rate depends on the conditions, present in the soil for nitrifying bacteria. Nitrification of NH4+ to NO3- preferably occurs under the following conditions:

• In the presence of nitrifying bacteria.
• Soil temperature > 20 °C.
• Soil pH 5,5 - 7,5.
• Sufficiently available soil moisture and oxygen.

How about that in using any Urea based N source.....You will loose up to 30% of that effective N through gasification (also the release of Co2) in that ammonification step?

Ammonium based N source's do not have that problem! You might only loose between 1-3%!

Different N source's are "available" to the plant at different rates and times.
There are plenty of Nitrate compounds and many different ones are used in making ferts.....
These need to be figured in to your NPK ratio's as you use them.

Other interesting facts are that the use of single forms of N change the pH of the soil/media/water via the roots and plant interactions.

Ammonia (a positively charged anion) based Nitrogen is taken up by the roots and they give back a hydrogen ion. Over time this will lower pH.

Nitrate (a negatively charged anion) based Nitrogen is taken up by the roots and they give back hydroxide ions. These hydroxide ions will combine with hydrogen ions (the combination makes water). In time this interaction, reduces the hydrogen in the soil/media/water and it will increase the pH.

Excess Ammonium can build up in plants and cause cell damage. This is part of why you dump,and refill hydro. Low temps (60 F and lower), over watering lead to low O2 levels in the media and that enhances ammonium levels to toxic amounts.

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