Today we’re taking a closer look at what many gardeners consider to be the big dog of fertilizer macronutrients: nitrogen. Most plants need a lot of nitrogen to get their green on, and it is often in short supply in the soil.

Nitrogen serves multiple crucial roles in plant growth and health. For instance, there are four nitrogen atoms in every green-pigmented chlorophyll molecule. Too little nitrogen = less chlorophyll = less green pigment = yellowing plant tissues. Beyond the cosmetic effect of lackluster color, a dearth of chlorophyll prevents plants from engaging in the photosynthesis to create necessary energy from the sun’s light. Nitrogen is also a key component of amino acids, the building blocks of protein. Those proteins are what allow water and other essential nutrients into plant cells. So basically, nitrogen is needed for plants to take in and use sunlight, water and essential nutrients – much of what they need to live and thrive.

Over 2/3 of the earth’s atmosphere is nitrogen, but as we mentioned in the Bacteria Basics post, plants can’t access that nitrogen without the help of soil microbes. Legumes like beans and peas have a reputation for nitrogen-fixing or demonstrating and apparent ability to grab nitrogen in the atmosphere and deposit it in the ground. But it’s really Rhizobia, the key group of soil bacteria that work with legumes, that are doing the work – the legumes just take credit for it. Rhizobia provide the enzymes necessary to break down atmospheric nitrogen into ions that the plants can actually use. But to give credit where credit is due, the plant’s roots provide a home for the bacteria and the roots slough off food for the bacteria, so the plant does play an important supporting role.

Unlike some other nutrients, nitrogen is mobile in plants. This means that young, growing tissues can steal nitrogen from older parts of the plant. That’s why yellowing of older plant tissue is a key visual indicator that there might be a nitrogen deficiency in your soil.

Nitrogen might have the biggest visual bang for the buck - nothing greens up your lawn like a nice blanket of nitrogen-rich fertilizer. But there’s more to plant health than color – we’ll cover the complementary roles phosphorus and potassium play in future posts.