Nitrogen

Plants require nitrogen in the largest amount, and depend on it to grow their roots, stems, leaves and vines. Nitrogen is also part of the makeup of all plant proteins so the nutritive value of food is dependent on it.

If nitrogen is taken from the air, you're probably wondering why plants can't just use that. Unfortunately, plants can only take up nitrogen in two forms: nitrate and ammonium. Fertilizer makers take the nitrogen from the air and combine it with hydrogen from natural gas to produce nitrogen fertilizers.

Common garden fertilizers are urea (46-0-0), ammonium nitrate (34-0-0), ammonium sulfate (21-0-0) and nitrogen solutions (28-32 percent nitrogen).