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Use Your Head: Human Hair Makes Good Plant Fertilizer

Weed/Disease/Insect Control

The hair, which is manufactured into cubes from barbershop and hair-salon waste, provides nitrogen for plants as it decomposes, according to a horticultural journal.

Wired News | December 30, 2008

Human hair could be used instead of chemical fertilizers for some plants like lettuce, new research in a horticultural journal suggests.

The hair, which is manufactured into cubes from barbershop and hair-salon waste, provides nitrogen for plants as it decomposes, just as natural-gas-derived sources like ammonia do.

"Once the degradation and mineralization of hair waste starts, it can provide sufficient nutrients to container-grown plants and ensure similar yields to those obtained with the commonly used fertilizers in horticulture," said horticulturalist Vlatcho Zheljazkov of  Mississippi State University.

All plants need nitrogen to grow. These plants form the basis of the proteins which eventually make their way into our bodies either directly through the consumption either of the plants themselves or of animals raised on plants. Our bodies turn those proteins into all sorts of useful things — like muscles — and some less useful things, like hair. In fact, studies carried out in the 1960s found that human hair contains about 15 percent nitrogen [pdf].

Nitrogen is ridiculously abundant. It composes about 75 percent of the atmosphere, but plants can't use it in its inert atmospheric form. Luckily, some microbes that grow with legumes pull this N2 out of the air and "fix it" into the reactive nitrogen that all living things use. Until the development of the Haber-Bosch process for cooking natural gas with more natural gas into nitrogen-rich ammonia, humans depended entirely on these microbes for the production of nitrogen. We either rotated other crops with legumes or used the  nitrogen left over from animal digestion as manure.

The last 50 years, however, have seen enormous increases in the use of synthetic fertilizers using ammonia from the Haber-Bosch process. Vaclav Smil of the University of Manitoba, one of the world's foremost experts on energy, estimates that 40 percent of the human population owes its existence [pdf] to synthetic fertilizers.

But all that nitrogen takes a lot of energy to produce. Smil has also estimated that the Haber-Bosch process uses about 1 percent of the world's total energy usage [xls], or about 150 gigawatts. That's about as much coal power as the UNited States plans to add between now and 2030, so low-energy alternatives to traditional chemical fertilizers could help reduce energy usage.

The new study, published in HortTechnology, shows that both lettuce and wormwood, the psychoactive ingredient in absinthe, grow about as well with hair as a fertilizer as they do with chemical fertilizers. The plants seem to be able to use about 50 percent of the nitrogen contained in the hair.

The only catch is that the hair takes a while to start decomposing and releasing nutrients into the soil, so it has to be paired with more fast-acting fertilizers.

(And that some people might find decomposing hair fertilizing their salad greens a little gross.)

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