Nitric Acid (HNO3)

Definition - What does Nitric Acid (HNO3) mean?

Nitric acid (HNO3), sometimes known as aqua fortis, is a corrosive acid that can be used to lower the pH of soil or water in a garden when acidification is needed to balance out alkalinity.

A colorless substance, nitric acid is commercially available, typically with in a concentration of 68 per cent in water. When the solution contains more than 86 per cent, nitric acid is considered 'fuming nitric acid'.

In other applications, nitric acid is also used as a strong oxidizing agent.

Note that nitric acid is not the same as muratic acid, which is actually hydrochloric acid.

MaximumYield explains Nitric Acid (HNO3)

While most plants require a neutral soil pH, some need either alkaline or acidic soils in order to thrive. For instance, blueberry bushes are well-known for their love of acidic soils, which is one reason they thrive in the Southeast’s native clay soils. However, not all soils have the right pH balance for plants, and gardeners must often take matters into their own hands.

Acidifying soil by applying nitric acid will reduce the pH level and free up nitrogen, helping to bolster plant growth. However, if too much nitrogen is released, it can cause overgrowth. Eventually, the high levels of nitrogen in the soil will cause damage the plants, or possibly result in little or no fruiting.

Nitric acid can also be used to reduce the pH of water, which is important for applying to in-ground gardens, but also applies to hydroponic and aquaponics systems, as well as to container gardening.

However, before acidifying the soil with any supplement or amendment, it’s important to first ensure that you do indeed have highly alkaline soil. A soil sample test can help you determine this. Many other symptoms can mimic high alkalinity, and applying a soil acidifier can cause unwanted problems, up to and including plant death.

There is also some controversy surrounding the use and application of nitric acid, due to its corrosive nature. Elemental sulfur can be used instead. A nitrogen-based fertilizer can also help to gently acidify soil without the potential drawbacks of nitric acid being applied directly.

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