Clover introduces nitrogen into the soil, acting as a natural fertilizer source for surrounding plants. As a legume, clover captures nitrogen gas from the atmosphere, which is normally inaccessible to most plant life. This process, known as nitrogen fixation, is a foundational element of healthy soil. Utilizing clover enriches the soil, reducing the need for synthetic nitrogen fertilizers.
The Symbiotic Process of Nitrogen Fixation
Clover cannot fix nitrogen alone; it requires a partnership with soil bacteria from the genus Rhizobium. These organisms enter the clover roots, prompting the plant to form small, round structures called root nodules. The bacteria live protected inside these nodules, converting atmospheric nitrogen (\(\text{N}_2\)) into a usable form.
The clover plant supplies the Rhizobium bacteria with carbohydrates produced through photosynthesis. In exchange, the bacteria convert the inert nitrogen gas into ammonium (\(\text{NH}_4^+\)). This ammonium is immediately incorporated into the clover’s tissues to build proteins and organic molecules necessary for growth. The nitrogen is stored within the plant itself, not released freely into the soil at this stage.
How Fixed Nitrogen Becomes Available to Other Plants
The nitrogen fixed inside clover becomes available to neighboring non-legume plants through nutrient cycling and decomposition. As clover grows, it constantly sheds old plant parts like root hairs and leaves, which break down in the soil. This natural turnover releases small amounts of nitrogen compounds throughout the plant’s life.
The most significant release occurs when the clover plant is terminated, either by mowing or tilling it into the soil, a practice known as using “green manure.” When the plant material dies, soil microbes break down the organic matter, consuming the clover’s nitrogen-rich proteins. This decomposition releases nitrogen back into the soil as ammonium and later nitrates, which are readily absorbed by other plants. Since a large portion of the fixed nitrogen is stored in the upper parts of the plant, allowing clippings to decompose on the soil surface accelerates this nutrient transfer.
Selecting and Utilizing Clover Varieties
Choosing the right type of clover depends on the specific goal for soil improvement or ground cover.
Crimson Clover
Crimson Clover (Trifolium incarnatum) is an annual variety known for its rapid growth and vibrant red flowers. It is often used as a winter cover crop, providing quick soil building and significant nitrogen fixation before its life cycle is complete.
Red Clover
Red Clover (Trifolium pratense) is a biennial or short-lived perennial that develops a deeper taproot system. This root structure is excellent for breaking up compacted soil and drawing up nutrients from deeper layers. It is frequently used for hay or forage, and its robust growth makes it valuable in rotation systems for long-term soil health.
White Clover
White Clover or Dutch Clover (Trifolium repens) is a low-growing perennial that spreads via surface runners called stolons, creating a dense mat. This variety is highly tolerant of foot traffic and close mowing, making it a popular choice for lawns or permanent ground cover. Its persistent nature allows it to continue fixing nitrogen year after year, providing a sustained release of nutrients.