기후변화로 인해 유기농법이 적합해 보인다

Organic farming methods, including extended crop rotation, may help U.S. agriculture to better cope with climate change.

Reading up on the nation’s deepening drought and failing crops last week, I came across an interesting piece by Jonathan Foley, director of the University of Minnesota's Institute on the Environment. 

Jonathan Foley

The venue was a roundtable of expert opinion in the New York Times, centered on the question, "How Can We Prevent Another Dust Bowl?"

Like most of the other panelists, Foley had the good sense to address a less alarmist and more interesting question, which in his case might be paraphrased like so: “What can Americans learn about growing crops in hotter, drier climate regimes?”

Short answer: a return to older, less industrialized and chemical-intensive farming practices can restore a resilience that been lost in modern methods:

Sadly, much of America’s commodity agriculture is especially vulnerable to climatic extremes – whether droughts, floods, heat waves or cold snaps. In particular, it is hard to imagine a system more susceptible to bad weather than the American corn and soybean belt.... 

You can drive from one end of the Midwest to the other and see almost nothing but corn and soybeans. If either crop fails (in terms of production or price), farmers are doomed. (Imagine a mutual fund that only invested in two companies. Wouldn’t that be incredibly risky?) Diversification – from two crops to dozens – would help guarantee at least some production and income each year.

Adding to the inherent vulnerability of any monoculture, Foley wrote, these particular crops have shallow roots and thus can’t reach for soil moisture that lies below the level of recent rain or irrigation. And they are grown with techniques that rob the soil itself of its ability to capture and store moisture.

The remedies Foley proposes are familiar elements of the agricultural approach often labeled organic or sustainable: Crop diversification and rotation, reduced tillage and enhanced tilth, organic fertilizers and so on. He closes with this provocative (and unanswered) question:

Extreme drought will happen again, guaranteed. Will American agriculture take a cue from this summer and prepare for it? 

A different time, a different take

Let there be no doubt that Foley knows whereof he opines. These points are derived in part from a paper he co-authored last spring in the journal Nature, a meta-analysis of 66 studies comparing yields from conventional and organic farm operations, raising 34 different crop species.

Back then, though, the conclusions that got the most attention were all about theadvantages of industrial ag. Under the headline “Organic farming is rarely enough,” Nature itself rolled out the findings this way:

Crop yields from organic farming are as much as 34% lower than those from comparable conventional farming practices, the analysis finds. Organic agriculture performs particularly poorly for vegetables and some cereal crops such as wheat, which make up the lion’s share of the food consumed around the world.

 Cereals and vegetables need lots of nitrogen to grow, suggesting that the yield differences are in large part attributable to nitrogen deficiencies in organic systems, says [Verena] Seufert [of McGill University in Montreal, the lead author].

 In conventional agricultural systems, farmers apply chemical fertilizers to fields while the crops are growing, delivering key nutrients such as nitrogen when the crops need it most. Organic approaches, such as laying crop residue on the soil surface, build up nutrients over a longer period of time. “There is not the synchrony between supply of nutrients and crop demand,” says Andrew MacDonald, a soil scientist at Rothamsted Research, an agricultural-science institute in Harpenden, UK.

At the time, those findings drew considerable fire from organic-farming advocates — a good example being Tom Philpott over at Mother Jones. He criticized the study for focusing narrowly on yields per acre while dismissing environmental impacts, and pointed out that while industrial ag may indeed look more productive in ordinary times, the authors themselves found a different story when the weather turns extreme:

“Soils managed with organic methods have shown better water-holding capacity and water infiltration rates and have produced higher yields than conventional systems under drought conditions and excessive rainfall.”

 In other words, organically managed soils deal with water better — both in conditions of drought and heavy storms (the frequency of which is also expected to increase as the climate changes). Soil rich in organic matter (well-decayed remnants of plants and other living creatures) bolster soil in weather extremes by helping store water in times of scarcity and by holding together and not eroding away during heavy rains.

 Given the increase in both kinds of weather events that's likely in our changing climate, Philpott wrote,

This raises a key issue: the paucity of funds we invest in organic research. According to the latest numbers I've seen, 4 percent of the food consumed in the United States — and 11 percent of the fruits and vegetables — is organic. How much of the USDA's research budget is devoted to organic research, including projects like developing proper organic seed lines? Less than 1 percent, the National Sustainable Agriculture Coalition's Ferd Hoefner recently told me. The other 99 percent goes to industrial ag — yet another de facto public subsidy to the agrichemical industry.

And it also suggests, at least to me, that the likely answer to Foley’s question — will Americans take a cue from this summer and begin to do things differently? — is not “you betcha!”

Here and there, hopeful signs

On the other hand, I saw some hopeful signs in the trade press — publications that speak to the actual farmers who are making the critical, on-the-ground decisions:

• Over at Ag Professional, an article promoting a bulletin of the Sustainable Agriculture Research and Education organization that advises farmers on saving water through conservation tillage, crop rotation and improved soil management.
• In CropLife, a report on achieving better soil quality through organic methods, including extended crop rotation and no synthetic fertilizer. 

Finally, I was impressed by a report on a 30-year, side-by-side comparison of organic vs. conventional cropping conducted by the Rodale Institute, which claims its Farming Systems Trial to be the longest-running test of its kind in America.

Given that the Rodale enterprises were essentially born in organic gardening and farming, it’s no great surprise that organic came out on top. But the methodology seemed fair enough, and the wide range of advantages – equal yields, richer soil, lower energy requirements, better drought tolerance and higher profits – is pretty compelling.