Soybeans as a Nitrogen Sink?

"Field Investigations of Manure and Synthetic Fertilizers on Agronomic Crops in Ohio" a talk by Keith Diedrick, OSU School of Environment and Natural Resources Soil Science Graduate Program.

This talk described the problem of too much fertilizer: large factory farms produce huge amounts of manure, which then must be disposed of. Whereas city and municipal biosolids (human waste) must be handled with extreme caution including up to a year of filtration, settling, fermentation, and more filtering, animal waste is treated differently. It is spread directly on conventional farm fields. Current agricultural practice includes spreading manure on top of snow (which then melts directly into local streams).

This research aimed to determine how much of this goop could be applied before the fields became over fertilized. This research should help farmers know when and how much animal waste they can apply to their fields. Ironically, the research was conducted on crops that actually require no fertilizer: soybeans. Because soybeans are legumes, they fix their own nitrogen and increased fertilizer has not shown increased productivity. While there may have been some productivity increase with increased use of manure, the limiting factor appears to be the production of dissolved forms of nitrogen in the soil. If farmers hypothetically wanted to limit the amount of fertilizer running off their fields, how much manure can they apply? Unfortunately, given that no groundwater or runoff samples were taken, it is not clear that this research can answer this question.

Maybe when will we stop researching factory farms and Roundup Ready soybeans and start researching solutions to the ecological and agricultural problems of today there will be better news to report here. This talk completely omitted the issue of antibiotics, surfactants, and other persistent organic pollutants (POPs) in manure and what effect these compounds might have on downstream ecology. I'm not just questioning the blatant narrow mindedness of this research, but the entire mindset that could lead someone to claim that this toxic manure is "just NPK" [nitrogen, phosphate, potassium] and that those three chemicals are the only thing important to plant nutrition and ecosystem functioning.