Some solutions to environmental problems are dizzyingly complex. Others are surprisingly simple.

Last week at FORTUNE's Brainstorm Green conference, the Environmental Defense Fund released its 2009 Innovations Review -- a collection of new ideas, products and services that are good for business and good for the environment. EDF asked me to help write the review, and what struck me is how many of the innovations were relatively easy to put into place.

You can read the report here, and I'll be blogging about several innovations in the days ahead. I want to begin by telling you about an agricultural innovation called "adaptive nutrient management" which I prefer to describe as social networking for farmers.

You know about social networks like Facebook, Twitter and MySpace. The Iowa Soybean Association has learned that when you get farmers networking -- in their case, face to face, usually after the growing season is over -- they learn to use fertilizer a lot more efficiently.

This matters because excess nitrogen fertilizer runs off fields into water supplies. And while the impact of nitrogen runoff on distant bodies of water is hard to measure precisely, it's a serious environmental problem.

According to Tom Morris, associate professor of soil fertility at the University of Connecticut:

"Agriculture is estimated to contribute 40 percent of the nitrogen pollution to the Chesapeake Bay, which is estimated to be 60,000 tons of nitrogen (annually) from agriculture. The amount of nitrogen contributed by agriculture to the Gulf of Mexico is estimated to be about 50 percent of the total, or about 825,000 tons from agriculture."

So-called dead zones where aquatic life cannot flourish are caused by this excess nitrogen, scientists say.

Of course, no farmer deliberately wastes fertilizer, especially since the costs of have been climbing -- the price is now about 60 cents a pound -- and corn and soybean farmers apply as much as 140 pounds per acre. The trouble is, farmers don’t know exactly how much fertilizer to use.

What's more, while using a little extra fertilizer adds to their expenses, not using enough can depress yields and dramatically depress farm incomes.

Tracy Blackmer, director of research for the Iowa Soybean Association, told me: "The penalty, traditionally, has been larger if you were short than if you over-fertilized."

In theory, the market should solve a problem like this, because no one wants to waste money on fertilizer. But markets don’t operate in theory.

What solves the problem is networking. Groups of farmers, typically neighbors farming similar soils in similar weather conditions, share information from their own on-farm studies. Together, they develop strategies for how and when to apply the least amount of nitrogen for the best economic and environmental results. Then they compare results, and further refine the process.

"The most important component of adaptive nutrient management is the winter meetings the farmers and their advisors attend to discuss their individual data and the data from their group," says Morris, who is working on a similar effort with Pennsylvania farmers whose land is part of the watershed that flows into the Chesapeake Bay.

Instead of top-down lectures from experts, collaboration is key. "We have often, in agriculture, provided information to farmers,” Morris says. But when farmers themselves organize the conversation, “you get rapid learning and rapid adoption of ideas."

"It is an iterative process," agrees Blackmer. "It guides where the next round of testing goes."

On average, Iowa corn and soy growers who joined in the program have reduced nitrogen use by about 30 percent, or about 30 pounds of nitrogen per acre, without reducing their profit per acre.

Information is power. Simple.

_{Inspecting soybean plants — Photo by Ken Hammond, USDA, Agriculture Research Service.}