All those snipped locks that are swept up after your haircut could be turned into crop fertilizer, researchers now say.

In addition to water and sunlight, plants need certain nutrients to grow, particularly nitrogen. While nitrogen is abundant in the Earth's atmosphere (composing about 78 percent of it), it is in the form of molecular nitrogen (two nitrogen atoms bonded together), which is unusable to plants.

For plants to take up nitrogen, it must be "fixed" into compounds such as nitrate (one nitrogen and three oxygen atoms), which plant roots can absorb from the soil.

While some plants, such as legumes, get their nitrogen through symbiotic relationships with nitrogen-fixing bacteria, others rely on fertilizers, whether organic (composted plant waste or animal manure) or inorganic (the man-made stuff you buy at the gardening center).

Previous studies had also shown that human hair discarded from barbershops and hair salons can also be a nutrient source for plants when combined with other compost materials. But it had not yet been proven that hair could act alone as an effective fertilizer.

To test this, Vlatcho Zheljazkov and his colleagues at Mississippi State University pitted waste hair against commercial fertilizers. They compared the productivity of four plants, lettuce, wormwood, yellow poppy and feverfew, under four different treatments: non-composted hair cubes, a controlled-release fertilizer, a water-soluble fertilizer, and no treatment.

Plant yields increased for the hair-fertilized plants compared to the untreated controls overall, but were still lower than for the commercial, inorganic fertilizers in lettuce and wormwood, which are fast-growing plants. Yellow poppy, however, saw higher yields for the hair treatment. (The results didn't differ between fertilizers for the feverfew.)

The researchers suspect that some of the difference between hair and the inorganic fertilizers is due to the time it takes for hair to degrade and release its nutrients. So hair shouldn't be used as a sole fertilizer, at least for fast-growing plants, they concluded.

Further research is still needed to see if human hair waste is a viable option for fertilizing edible crops though because of possible health concerns.

The results of the study were detailed in a recent issue of the journal HortTechnology.