My grandfather had a small wagon equipped with a reel on the back. Two chain-like mechanisms with metal bars between them ran the length of the wagon bed, carrying material to the reel where it could be thrown out onto a field.

It always amazed me that my brothers and I could work 30 to 40 minutes filling up the wagon bed with manure, but the spreader could empty its load in less than a minute. (My wife’s grandfather, who also owned a small farm, liked to say this was the only implement a farmer wouldn’t stand behind.)

Few environmentalists have stood in a field and watched a manure spreader at work. If they had, they wouldn’t make claims that the world can feed itself with nutrients from organic sources.

Two scientists with the Potash and Phosphate Institute of Canada recently addressed this issue in an article titled "Organic Agriculture Depends on Inorganic Nutrients." Tom Bruulsema and Adrian Johnson note that despite all propaganda about the growth of organic farming, it still accounts for only 2 percent of food sales in North America.

Organic standards require nutrients to be chiefly from organic sources, such as manures and composts, and preferably from on-farm. "The major certifying bodies exclude use of synthetic and soluble forms of nitrogen and phosphorus fertilizers that transformed agriculture beginning in the 19th century," the authors said. "They differ on allowable forms of potassium fertilizer."

Research shows that on-farm nutrients limit productivity even if the farm can produce enough manure. One study found that crops grown organically produced only 44 percent to 75 percent of the yields of those grown inorganically. Low phosphorus and sulfur levels on the organic farms not only kept yields low, it said, but also could limit nitrogen fixation by legumes.

"As long as the percentage of the land area farmed organically remains small, supplying organic nutrients from neighboring farms won’t be a problem," the authors say. "Composts, crop residues and animal manures all contain nutrients derived in part from commercial fertilizer nutrients, applied at some point in the past."

Even after many years of transition to organic farming, soils still contain phosphorus and potassium built up by commercial fertilizer use, they note. So organic farmers benefit from this long history of applying commercial fertilizer nutrients.

It’s difficult to visualize farmers in the Delta or south Georgia or the North Carolina Blacklands finding farmers with enough cows to meet even a fraction of the nitrogen, phosphorus and potassium needs on their cotton or rice farms. My grandfather put 20 to 25 cows and calves up in the barn at night during the winter months and still produced only enough manure to fertilize about an acre.

It’s another example of something sounding easy when you’re writing about it in an air-conditioned office 1,000 miles from a farm.

e-mail:flaws@primediabusiness.com