The Effect of Nitrogen Levels on Worms

Worms and Nitrogen

• There are approximately 2,700 species of earthworm worldwide. There have been too few studies conducted to make any general statements about the effects of nitrogen on all of them. Moreover, they are mobile, so changes in nitrogen levels in one part of a body of soil might precipitate short migrations toward or away from nitrogen concentrations, depending on how those concentrations interact with carbon and other elements in the soil. Worms produce nitrogen in their body slime and excretions, so the soil nitrogen levels and worms exist in a recursive relationship.

Natural Cycles

• Worms create nitrogen when they eat in a similar way to humans. Both worms and humans produce a liquid waste, or urine, as part of their metabolic process. Human urine is high in nitrogen and so is worm urine. Worm composters who collect this liquid call it "worm tea," and it is a highly prized fertilizer for organic gardeners. Bacteria in the soil use various kinds of nitrogen in a process that breaks down carbon-heavy matter, like straw, wood and dead leaves. The cyclical variations in nitrogen levels in soil undergoing this process do not appear to have any appreciable effect on worms.

Anaerobic Decomposition

• The addition of nitrogenous material to compost piles -- grass clippings, fresh kitchen scraps and even human urine -- accelerates the breakdown of carbonaceous materials, which worms will then eat and excrete. Heavy doses of nitrogen can unbalance this process, and in static environments promote anaerobic decomposition, which will repel worms because of the lack of oxygen. Worms have also been observed fleeing heavy doses of synthetic nitrogen fertilizers. One explanation for this repellent effect is that the synthetic nitrogen contains salts that worms find inhospitable.

Industrially Tilled Fields

• The numbers of earthworms in most fields that have received high annual doses of synthetic nitrogen fertilizers are substantially lower than worm population density in the soils of organic gardeners. Industrially cultivated fields are also tilled each year, which exposes turned soil to oxygen when nitrogen is added, creating a feeding frenzy of bacteria that releases large amounts of carbon rapidly into the atmosphere where it is no longer available in organic form as worm food. Tillage itself is also disruptive to the worms, so the degree to which nitrogen levels are responsible for smaller worm populations is difficult to determine.