Element Hunting: Nitrogen

Element Hunting: Nitrogen ( a macro-nutrient) 

Before diving into this week’s topic, let’s define a few crucial terms that are used to discuss the role nitrogen plays in your garden and life in general.

Use of the term organic:

• A chemist or physicist will tell you that just about any compound containing a Carbon is organic
• A gardener will use the term organic to describe fertilizers derived exclusively from plants and animals*

*since we’re referring to our medical marijuana gardens, let’s use this definition.

Minerals:

• Naturally occurring, but inorganic
• Sourced neither from plants nor animals, but instead from crushed rocks or chemical processes

There are 18 elements required for plants to live: 9 of which are macronutrients & 8 of which are micronutrients.

C, H, O, N, P, K, Ca, Mg, S, B, Cl, Cu, Fe, Mn, Mo, Zn, & Ni  (&& many argue Si should be added to the list)

Plant available forms of these elements are:

PO₄^3-, HPO₄^2-, H₂PO₄^–/ K⁺/Ca²⁺/Mg²⁺/SO₂, SO₄^2-/H₃BO₃, B₄O₇^2-/Cl^–/ Cu⁺, Cu²⁺/ Fe^2+, Fe³⁺/Mn²⁺/MoO₄^2-/Zn²⁺

This week on the Bounty Blog we will be focusing on Nitrogen. Before our element of choice can go to work, we need to understand how our plants (and our own bodies!) consume it.

Plant available forms of Nitrogen: (Ammonium) NH₄⁺ & (Nitrate) NO₃^–

Nitrogen:

• Nitrogen gas (N₂) makes up around 78% of Earth’s atmosphere
• It is necessary for metabolic processes
• Makes up part of the chlorophyll molecule (C55H72MgN4O5), hence it is crucial for the process of photosynthesis
• Aids in development of new plant tissue
• Most plants in a garden are about 3%-4% Nitrogen by weight
• This mobile element is transported within the plant whenever needed
  • This is why yellowing of older leaves is one of the first signs of Nitrogen deficiency. New growth will always be favored and Nitrogen will be re-located to those areas first. For more information on what Nitrogen deficiency looks like and how to prevent it, check out my Bounty Blog post from a few weeks ago here.

We as humans need N to make amino acids, proteins, DNA, and RNA, and while it’s practically everywhere, our bodies can’t make use of it since it’s NOT biologically available for us to just grab and consume all willy-nilly.

So what helps us access N? We simply have to eat plants, or something that ate plants.

A great video that does a beautiful job of covering the Nitrogen cycle can be found here.

Even plants struggle to take advantage and use the available atmospheric Nitrogen without the help of bacteria. These Nitrogen-fixing bacteria do so with a special enzyme, nitrogenase, which is the ONLY biological enzyme that can break apart the triple bond holding N₂ together.

Side-note: N₂ exists in nature as an extremely stable, stubborn triple-bonded molecule that never wants to be pried apart. There isn’t just 1 bond, there are 3! As you can imagine, it requires lots of energy to break those triple bonds apart. But once this has occurred, Nitrogen can then exist in different forms: NH₃, NH₄⁺ and NO₃^–.

Okay, so once plants acquire available Nitrogen—either synthetically through direct administration of nitrates or organically using the soil food web—plants can then take water, light, and carbon dioxide and make, well,  just about everything!

Let’s explore how plants use Nitrogen in metabolic processes and why Nitrogen is also crucial for photosynthetic processes.

Photosynthesis basically occurs in two stages:

Light dependent reactions

• a series of light dependent reactions resulting in the production of NADPH and ATP— just think ENERGY, lots of energy.

*click picture to enlarge

There’s a Nitrogen in play here  NADPH (energy) which after production serves as the reducing power for sequential reactions occurring during the second stage of photosynthesis, during…

The light independent reactions

• Known as Calvin cycle or carbon fixation, this cycle converts carbon dioxide and water into G3P, and eventually into any carbohydrate.

*Click picture to enlarge

As you can see, Nitrogen plays a crucial role for plants; without it photosynthesis could not occur.

In Summary, Nitrogen is a crucial and abundant element, yet inaccessible to both humans and plants, even though it makes up about 78% of our atmosphere. Humans must rely on plants as a source of Nitrogen, and plants must rely on nitrogen-fixing bacteria to release the triple bond and create accessible, usable forms of the element.

So the unsung heroes, yet again, are bacteria since they kick-start a global cycling of elements, in this case Nitrogen:

N₂ →bacteria split the triple bond→ NH₃, NH₄⁺ and NO₃^–  → plant available Nitrogen enter metabolic cycles→ photosynthesis takes place with given availability of light, water, CO₂ → carbohydrates →  food/energy for the plant → life.

A video that explains photosynthesis extremely well can be found here.

Hope this has helped, happy farming everyone!