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.

Important Minerals

Plants need minerals to grow big and produce fruit (実がなる). The three most important minerals are nitrogen (窒素), phosphorus (リン), and potassium (カリ). Each of these minerals does a different job that helps make plants healthy.

            Nitrogen is the most important of these three minerals. Plants absorb (吸い取る) more nitrogen than any other mineral. It helps plants develop protein, which is necessary to develop healthy cells (細胞) as they grow. Plants also need nitrogen for photosynthesis (光合成) – the process of turning sunlight into energy to grow larger and produce fruit.

            Phosphorus is also important for photosynthesis because it helps plants store energy. It also helps plants grow and develop.

            The last mineral is potassium. Potassium helps plants grow strong roots (根っ子), and makes them more resistant to diseases (病気に強い) and cold temperatures. In addition, it helps plants produce fruit.

            How do plants get these minerals? They absorb them from the soil (土) using their roots. So, having healthy soil is one of the most important things about having a healthy garden. The easiest way to make sure that your soil has enough nitrogen, phosphorus, and potassium is to use industrial fertilizers (産業肥料). However, in our garden we try not to use industrial fertilizers. Instead, we try to plant plants that will provide these minerals to our plants naturally. These are called dynamic accumulators. In the next article, we will introduce some of our favorite dynamic accumulators.

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