Nitrogen Fixing and Dynamic Accumulators

Nitrogen Fixing and Dynamic Accumulators

Nitrogen (窒素) is one of the main plant nutrients associated with plant growth. However, plants cannot absorb nitrogen as gas (N₂) from the air because they require “fixed” forms of nitrogen known as nitrates (NO­₃^-). Some plants, known as ‘nitrogen fixers’ interact with certain types of microbes to transform nitrogen gas into nitrates.

The microbes live on the roots of nitrogen-fixing plants and turn atmospheric nitrogen (‘breathed’ in by the plant) into nitrates that the plant can use as food. In exchange, the nitrogen-fixing plant provides the microbes with carbohydrates (炭水化物). This relationship enables the plant to produce nitrogen-rich leaves and seeds. As the leaves and fruits fall to the ground or as root die-back, the nitrogen becomes available to other plants in the surrounding area, thus benefiting the whole system.

Other nutrients, like potassium and phosphorus, will also be depleted (枯渇した) as we harvest food from the plants, so these need to be replaced in other ways. In a forest garden plants called, dynamic accumulators (like comfrey (コンフリー) for example) are often used to fill this role.

Dynamic accumulators are plants that have deep roots. They can absorb nutrients from parts of the soil that other plants cannot reach. The nutrients accumulate in their roots and leaves. As leaves and roots die back, the nutrients are added to the topsoil and become available to surrounding plants.