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What Should Be Done About the Excess Nitrogen Fertilizer That Is Claimed to be Wreaking Havoc with Earth's Forests?
Volume 6, Number 49: 3 December 2003

In a recent News Feature in Nature, Nosengo (2003) frets about the findings of James Galloway, an environmental scientist at the University of Virginia in Charlottesville, who estimates, according to Nosengo, "that almost half of the nitrogen spread onto fields is not taken up by crops but instead washes away."  What happens to this unused nitrogen?

Much of it is converted to ammonia and NOX, which makes its way into the atmosphere from whence it ultimately rains down upon earth's forests, many of which are claimed to be receiving an overdose of this normally essential element.  Too much of a good thing can sometimes be bad for an organism, however, and such is claimed by some to be the case with today's forests.

Nosengo relates what Aber et al. (1989) opine to be the likely course of events in this situation.  The forest initially thrives, but at some point in time the input of nitrogen exceeds demand.  Then, when the trees cannot absorb all the nitrogen that is available, it builds up in the soil, mostly as negatively-charged nitrate ions that attract positively-charged calcium and magnesium ions and ultimately carry them down to the water table, thereby depriving the trees of these much needed nutrients.  Thus "weakened," in Nosengo's words, "the trees become increasingly vulnerable to frost, drought and parasites," while at the same time, "rising soil acidity causes a loss in biodiversity in the undergrowth."

"So," Nosengo asks, "how can we save our forests?"

A number of possible actions are listed, all of which are considered to be technically feasible.  However, they are described as being so expensive that no one currently employs them.  In addition, Nosengo quotes Galloway as saying, and quite appropriately, that we currently need nitrogen fertilizer to grow sufficient food to feed the world and "we will need it more in the future."

Faced with this conundrum, a proposed "solution" will be presented at an international meeting that will convene next October in Nanjing, China, one of several countries that are said to have "no intention of reducing their use of nitrogen."  Nevertheless, the aim of the conference, according to Nosengo, "is to propose a 'Nanjing protocol' to address the issue of nitrogen at a global level."

Sound familiar?  The use of a substance that is essential for proper plant growth and development, including production of the food we need to survive, is said to produce a gaseous byproduct that is bad for the biosphere.  In addition, although the substance is known to be expensive to regulate, it is nevertheless slated for regulation on a global scale via the accords of an international protocol that will be named after the city where it will be proposed.  Is this deja vu or what?

Well, we propose to take the analogy of the Nanjing and Kyoto Protocols even further, by suggesting that we solve the so-called problem of excess nitrogen fertilizer use by doing what we suggest should be done about the so-called problem of excess anthropogenic CO2 emissions, i.e., absolutely nothing.  Our rationale for this policy of "dual inaction" is solely scientific; and it is doubly to be preferred over the two protocol prescriptions.  Why?  Because it actually solves the "twin problems" of the two protocols at one and the same time.  Here's how it works.

Earth's forests would have the capacity to significantly reduce the rate of rise of the atmosphere's CO2 content as a consequence of the growth stimulation provided by the aerial fertilization effect of the extra CO2 if sufficient soil nitrogen were available to them to enable them to fully respond to the extra CO2 [see our Journal Reviews of Schafer et al. (2003) and Finzi and Schlesinger (2003), as well as Growth Response to CO2 with Other Variables (Nutrients - Nitrogen: Trees) in our Subject Index].  Likewise, earth's forests would have the capacity to significantly reduce the rate of loss of nitrogen from forest soils if sufficient aerial CO2 were available to them to provide the extra growth needed to remove the excess nitrogen from the soil and keep it from being lost to ground water.  Hence, the solution to each of the perceived problems is to let them coexist, so that the excess of each supplies the need of the other.

This plan of (non)attack could perhaps be called a reciprocating supply-and-demand approach.  In one case, lack of soil nitrogen keeps the rate of CO2 removal from the atmosphere via earth's forests far below their actual carbon sink potential; while in the other case, lack of aerial CO2 keeps the rate of nitrogen removal from the soil via forests far below their actual nitrogen sink potential.  Thus, when both of these substances (atmospheric CO2 and soil nitrogen) are allowed to rise simultaneously, the potentials for forests to remove each of them from their respective atmospheric and soil reservoirs also rise together, as does the productivity of the entire biosphere, all without any unnecessary interventions on the part of man.  It's truly a win-win-win-win (count 'em) situation.

Clearly, more experiments and subsequent analyses will be required to determine the absolute magnitudes of the interactive processes germane to this scenario; but at least there is now a simple conceptual framework for going about the task of obtaining those results.  Compared to the almost unimaginable costs associated with the tremendous interventions that would be required by the standard solutions of the Nanjing and Kyoto Protocols, the costs of such an experimental program would be truly miniscule.  Logic would thus suggest that these important studies be begun as soon as possible.

Sherwood, Keith and Craig Idso

Aber, J.D., Nadelhoffer, K.J., Steudler, P. and Melillo, J.M.  1989.  BioScience 39: 378-386.

Finzi, A.C. and Schlesinger, W.H.  2003.  Soil-nitrogen cycling in a pine forest exposed to 5 years of elevated carbon dioxide.  Ecosystems 6: 444-456.

Nosengo, N.  2003.  Fertilized to death.  Nature 425: 894-895.

Schafer, K.V.R., Oren, R., Ellsworth, D.S., Lai, C.-T., Herrick, J.D., Finzi, A.C., Richter, D.D. and Katul, G.G.  2003.  Exposure to an enriched CO2 atmosphere alters carbon assimilation and allocation in a pine forest ecosystem.  Global Change Biology 9: 1378-1400.