Chris Richards for The New York Times

Last week, the government doled out more than $80 million in stimulus money for biofuels research, much of which will be focused on algae research.

But a recent study, published in the journal Environmental Science and Technology, suggests that algae production is energy intensive and can end up emitting more greenhouse gases than it sequesters. Other biofuel crops like corn, canola and switchgress result in a net carbon dioxide uptake, the study found.

The main reason for this is that fertilizers have to be directly delivered to the pool of water that algae is growing in, said Andres Clarens, an assistant professor of civil engineering at the University of Virginia Civil and a lead author on the paper. And fertilizers are very energy intensive to produce.

Corn and switchgrass can draw nitrogen from soil, which reduces the overall amount of fertilizer required, he said. In addition, crop rotation can help replenish soil nutrients.

“Nutrients are going to be the limiting factor,” Dr. Clarens said. “We’re humans. We need to eat dinner, and you can’t expect to have algae that provides a bunch of energy without feeding it nutrients.”

Dr. Clarens added that one notable benefit of algae is that it grows atop water and does not compete with food crops for land space. Algae also has a higher energy yield per unit area than other biofuels sources, including corn and switch grass.

Advocates of algae biofuel said it was too early to make predictions about algae fuel, because research is in developmental stages.

“The algae biofuel sector is still in its infancy,” said Gerry Jardine, a director at Valcent, a Vancouver, Canada based company developing algae biofuel,

“It is too early to make predictions on related energy costs pertaining to the production,” he added.

The paper suggests that one way to reduce the environmental impact of algae is to draw municipal wastewater into algae plantations, as a source of nitrogen and phosphorus.

This could reduce the amount of fertilizer required, said Dr. Jardine.

Numerous companies, large and small, are investing resources in algae biofuel research, including Exxon Mobil, which last summer devoted $600 million to the endeavor.