From 1998 to 2008, the researchers evaluated and compared potential management strategies for reducing nitrogen and nitrate nitrogen levels in soil and groundwater.
The first study showed that onions used only about 12 to 15 percent of the fertilizer nitrogen applied to the crop. Much of the remainder stayed in the top six feet of soil. The next year, Halvorson and his colleagues planted corn on the same land and found that it recovered about 24 percent of the fertilizer nitrogen that had been applied to the onion crop.
Following that study, the scientists grew alfalfa on the land for five years, then followed it with a watermelon crop, followed by a corn crop. In the first year that the corn was grown, an unfertilized control plot yielded about 250 bushels of corn.
By comparison, a plot fertilized with 250 pounds of nitrogen per acre yielded about 260 bushels, a small increase that required a significantly higher investment of time and money. Additional corn studies following onion in rotation showed corn was a good residual nitrogen scavenger crop.
To put that in perspective, keep in mind that farmers (especially corn farmers) often over-apply fertilizer. As George Naylor, the corn farmer featured in Michael Pollan’s Omnivore’s Dilemma, said, “You don’t want to err on the side of too little.” Except maybe you do. Corn may be a nitrogen fiend — yet even so, the crop in the study was able to take advantage of the fertilizer put down in an earlier rotation and yield almost as much.
I imagine many a corn farmer would be shocked to hear that. And even though for a farmer on the edge (as most are) every bushel counts, savings on fertilizer and the fuel needed to spread it would more than make up for the difference in yield.
If nothing else, this study should make it clear that monocropping has got to go. If farmers are going to reduce their carbon footprints and improve water quality (i.e. use less synthetic fertilizer and fuel), then we need to return to polyculture farming.
Too bad the USDA won’t let you do that and keep your subsidies (at least not if you grow corn, wheat or soy) — unless, that is, you can worm your way into this pilot project. By law, no fruit or vegetables can be grown on any acre that receives a commodity subsidy. So here’s hoping that Tom Vilsack and his team pay attention to their own research.