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.

Dead Flowers and the Giant Juicer

As someone who's known the value of compost, I can appreciate the value of detritus in nature, especially in the desert where organic carbon is often the limiting factor in vegetative growth.
Are plants worth more dead or alive? Where does all the detritus go? Why do some ecosystems produce more dead standing matter than others? What does this say about ecosystem health or productivity? To answer these and many other fascinating ecological conundrums, ecologists would like to measure and compare the efficiency of different systems. Efficiency is conceived as the ratio of production (new tissue) to biomass (existing tissue). But,

"...there is another way of looking at the figures of productivity in relation to biomass. This is to say that biomass as we define it is a quite unrealistic way of measuring the standing crop of a community. For example, is it justifiable to treat the dead wood and bark of a tree as if they were in any direct way causally determining the rate at which that tree makes new dry matter (or fixes energy?) Nearly all the differences in community productivity that we see between community types arise because we choose to define biomass in this way. It might be much more sensible to define biomass in terms of weight of living tissue (if we could find a way to measure it)." p.720 Ecology. Begon, Harper, and Townsend.


To better compare measures of productivity the authors want to separate structural and detritus from actual living tissue. I suggest using a Giant Juicer (GJ) to strain out all the structural fibers...of course, their proposal begs the question of what it means to be "living" versus nonliving, because to measure dry weight they would evaporate the juice, leaving, at the bare minimum, most of the intracellular structural components. Are proteins alive? Maybe they should just measure the weight of DNA and RNA?


Measuring an accurate ratio of production to biomass (P:B) is useful for figuring out all kinds of stuff, e.g. how ecological succession affects productivity and whether natives or invasives sequester more carbon (i.e. are more productive). NB: since cropland productivity has been measured at utilizing nearly 10% of the available solar flux it is certain that native flora are usually suboptimal. (Limiting nutrients are the cause of suboptimal production.) But that judgement of "suboptimal" might only point to a flaw in our measurements: perhaps a long-term measure of the sustainable productivity would yield different results (organic farming?)...or perhaps this simply reiterates the hope of the Panglossian Paradigm in ecology, that natural systems are somehow "better" than man-made systems. Indeed, this does appear to be part of the assumptions of Permaculture (taking natural ecosystems as the model for our own human habitats).

It does seem that most living organisms in natural ecosystems create more habitat for other organisms simply as a side-effect of building their own tissues (parasites, detrivores) and homes (e.g. burrows, beaver dams). Humans appear to be the glaring exception to this logic, in that we more frequently destroy habitat (antibiotics, monocultures, cities) than create it.


But all these speculations must remain entirely philosophical and equivocal until my Giant Juicer can provide quantitative certainty...