All plants, including cannabis, require nitrogen to thrive. Understanding how cannabis plants uptake and utilize nitrogen is essential for achieving optimal growth and yields. Let's explore the basics of the nitrogen cycle and its importance for cannabis cultivation.
Forms of nitrogen
Nitrogen, comes in three primary forms: ammonium, nitrate, and urea. Ammonium (NH4+) carries a positive charge, nitrate (NH3–)carries a negative charge, while urea ((NH2)2CO) carries no charge.
Natural processes in media
Once these nitrogen forms are introduced into the growing media, natural processes kick in. Bacteria play a vital role, converting urea to ammonium or ammonium to nitrate. This latter conversion releases hydrogen ions, increasing media acidity.
Urea conversion
Urea undergoes rapid conversion to ammonium in the soil, usually within two days. Both urea and ammonium are often grouped together and referred to as ammoniacal nitrogen.
Media nitrogen uptake by plants
When plants absorb nitrogen, they typically release a molecule with the same charge to maintain internal pH. This process can also alter the pH of the media surrounding the roots.
pH effects of nitrogen uptake
Ammonium (NO4) uptake and pH
When plants absorb ammonium, they release hydrogen ions (H+) into the media. This increases the acidity of the media over time, decreasing the pH.
Nitrate (NO3) uptake and pH
Plants take up nitrate by releasing hydroxide ions (OH–). These ions combine with hydrogen ions to form water. The reduction in hydrogen ions eventually reduces the media acidity increasing the pH.
Nitrate (NO3) absorption variations
Sometimes, plants absorb nitrate differently, either by taking in hydrogen ions or releasing bicarbonate. Like hydroxide ions, bicarbonate reacts with hydrogen ions and indirectly raises the media pH.
Understanding these processes helps in choosing the appropriate fertilizer to manage media pH. Depending on the nutrients present, the media's acidity or alkalinity can be adjusted to optimize plant growth.
Risks of ammoniacal nitrogen
Plants can only absorb a certain amount of nitrogen at a time. However, they have the ability to store excess nitrogen for later use if needed.
Nitrate (NO3) vs. ammonium (NH4)
Plants can safely store nitrate, but too much ammonium can harm cells. Thankfully, bacteria in the media convert urea and ammonium to nitrate, reducing the risk of ammonium buildup.
Factors affecting ammonium (NH4) levels
Certain conditions like low temperatures, waterlogged media, and low pH can prevent bacteria from converting ammonium. This can lead to toxic levels of ammonium in the media, causing damage to plant cells.
Symptoms of ammonium (NH4) toxicity
Upward or downward curling of lower leaves depending on plant species; and yellowing between the veins of older leaves which can progress to cell death.
Preventing ammonium (NH4) toxicity
When it comes to nitrogen breakdown of a nutrient solution, it's crucial not to exceed 30% of the total nitrogen as ammoniacal nitrogen. Higher levels can lead to toxicity, severe damage, and even plant death.
Ideal nitrogen ratio for cannabis
Best nitrogen (NO3) ratio
Research shows that medical cannabis plants respond best to nitrogen supplied in the form of nitrate (NO3). This helps them produce more flowers and maintain healthy levels of secondary compounds.
Safe ammonium (NH4) levels
While high levels of ammonium (NH4) can be harmful to cannabis plants, moderate levels (around 10-30% of the total nitrogen) are considered most suitable. This level helps prevent leaf burn and pH changes in the media.
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