One species of amoeba can transport and plant bacteria when it runs short of its normal food, bacteria in the soil. A recent study is the first proof that anything smaller than an ant can “farm,” and shows how evolution can produce alternative strategies to meet the challenges of survival.

Image: M.J. Grimson & R.L. Blanton

The single-celled amoeba Dictyostelium discoideum has no brain, but its complicated social cycle enables farming.

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Discussion Questions

1. What is the working definition of “farmer” in the article, and how do these amoeba satisfy this definition?
2. What are some of the social and economic benefits of human agriculture, and how are they rooted in farming? How did the advent of farming change human history?
3. How did the study author determine that it’s “normal” for these amoeba to carry bacteria?
4. Why does the article say that evolution would favor a species that comes up with alternative survival strategies?

Lesson Plans/Activities

1. Be an amoeba detective. Ask students to collect soil samples and, using a compound microscope, have them record the protozoa they can see on this worksheet, or something similar. Have students compare the protozoan’s shape, movement, cyst formation and feeding patterns. (Students can use this resource to help them with the identifications.) Have students discuss the relationship these organisms might have with their ecosystem. Recommended for grades 8-10.
2. Amoebas and me. Have students research the relationship between amoebas and people. Ask them to develop a skit that presents this relationship.
3. Who else is down on the farm? Ask students to research other organisms that farm and write a paper, or conduct a more creative activity, that describes their farming techniques.

Minirhizotrons took these photos depicting root growth over a three-week period in the summer of 2011. Image courtesy of ORNL.

Teeny little video cameras called minirhizotrons snapped these photos of wetland plant roots. The cameras will help scientists anticipate how the plants might respond to climate change.

Minirhizotrons give scientists at the Oak Ridge National Laboratory a technological boost by allowing them to study living roots, especially the really small ones, without harming the plants. By tracking the life and death of roots in their real-life soil environments, with a few manipulations here and there, scientists can better understand what effects increasing temperatures and carbon dioxide levels will have on wetland ecosystems.

The specific wetlands in question are bogs, which are carbon-rich, but nutrient-poor environments. In other words, bogs collect a lot of carbon deep in their soil due to large buildups of dead plant matter. However, their soils don’t have a lot of nutrients to give back to living plants, making them tricky places for plants to grow.

Roots are responsible for transporting water and nutrients to the rest of the plant. So, in bogs, they have to work extra hard to keep plants alive.

Scientists will use the minirhizotrons in one of Minnesota’s black spruce bogs to track how roots react to their climate-change-mimicking manipulations.

Bogs cover only 3 percent of the Earth’s surface. So, why should we care what happens to them?

Because they store nearly one-third of our terrestrial carbon. Thus, if the planet continues to warm, scientists predict these bogs will dry out and release tons of carbon into the atmosphere, exacerbating warming.

Yikes.

Image courtesy of ORNL. Source: Method of studying roots rarely used in wetlands improves ecosystem research

Hunger season approaching?

In some places, the harvest is preceded by “hunger season,” when stored crops are exhausted but the new crop is not ready. For many reasons, we’re wondering if the Earth is entering a long hunger season:

Food prices reached records in February, which may even have helped spark the political unrest that swept the Middle East. As Lester Brown of the Earth Policy Institute notes, a 10 percent rise in the price of wheat barely budges the price of bread in developed countries, but directly boosts the price of chapattis in India.

The population is expected to reach about 9 billion by 2050, and 3 billion people with rising incomes have a growing appetite for grain-intensive animal protein.

The World Food Program estimates that one person in seven goes to bed hungry. One reason is poverty: In this world, only the poor are hungry. But other reasons are related to supply and demand:

The end of civilization?

Depleted soil is a legacy of many failed civilizations, wrote soil scientist David Montgomery1 of the University of Washington. “In recent decades, archaeological studies confirmed pronounced episodes of soil erosion associated with the rise and subsequent decline of civilizations in the Middle East, Greece, Rome, and Mesoamerica, as well as other regions around the globe.”

Indeed, Montgomery writes, “a limiting lifespan of an agricultural civilization can be estimated by the time needed for conventional agriculture to erode through the native stock of topsoil,” which “predicts reasonably well the historical pattern of a 500- to several-thousand-year lifespan for major civilizations around the world.” These calculations, he says, support the argument “that it was not the axe that cleared forests but the plow that followed that undermined many ancient societies.”

Soil health is often gauged by the percentage of organic matter — the decomposing plant material that feeds microbes and soil animals, and enables soil to hold water and nutrients, says Jane Johnson, a soil scientist with the U.S. Department of Agriculture in Minnesota. “Most of the characteristics that we associate with high quality soil are directly or indirectly linked to soil organic matter.”

Therefore, the emphasis on protecting and improving soil so it can feed an ever-growing population often comes down to the level of organic matter. In the United States, much of the cropland has already lost 30 to 50 percent of its organic matter since Europeans started farming a couple of centuries ago, says Rattan Lal, a professor of environment and natural resources at Ohio State University.

Most productive soil in Africa and Asia has lost 70 percent to 80 percent of its organic matter, says Lal, an outspoken defender of the soil, and long ago crossed the line toward ruination. “There is a threshold — about 1.2 percent to 2 percent of carbon [the usual measure of organic matter] — to maintain soil health, water retention and other soil services.”

Many soils in Africa, India and China have only one-tenth that much carbon, Lal says, and that leads to a truckload of trouble. “When you add fertilizer, it washes into the groundwater because the organic matter is not there, and the same goes for pesticides and herbicides. These chemicals wash into rivers or the groundwater, or enter the atmosphere, where they cause human health and environmental problems,” without conferring much benefit to the crop.

Lal says a train in his native Punjab, India is dubbed the “Cancer Express” because it travels through a region where “many people are prone to cancer because of pollution of the drinking water. The soil does not have the capacity to hold water and pollutants. That is what the biological health of soil does; you get microbial decomposition, absorption of organic matter and retention of water. If crop residues are taken away, if dung is taken away for cooking, the soil has nothing left to provide the services. It essentially becomes a sand culture.”

Good soil, great benefits…

About the only bright spot in the grim picture of soil destruction is this: many solutions offer synergistic benefits. Leaving a crop residue on the surface cuts wind and water erosion, and raises the level of organic matter. Conservation tillage cuts erosion, reduces the need for irrigation, and stores carbon in the soil. Smart irrigation reduces water use, and the need to plant on steep, erodible slopes.

Soil – some still call it dirt – is not as popular as Facebook or Dancing with the Stars. But it’s a whole lot more important. “Our ability to feed humankind in the future depends on a stable, improved soil resource,” says Jerry Hatfield, director of the Agricultural Research Service lab in Ames, Iowa.

Or, as University of Minnesota soil scientist William Larson once said, “Soil is that thin layer on the planet that stands between us and starvation.”

Enough with the problems. Let’s look at some serious soil solutions.

Washing away

Because water erosion can rapidly flush nutrients, mineral soil and organic matter from hilly land, the battle against water erosion has been a focus of American farmland conservation since the 1930s. One common prescription is contour planting; rows planted across the slope are more resistant to erosion than those running up the slope.

A standard way to protect soil is to leave crop residues in place after harvest, but bioenergy proposals often suggest that these wastes be fermented into cellulosic ethanol. The best solution depends on the situation, Johnson says. “If the land is highly erodible, we should not take residue. But if the landscape has a low erosion risk, then if we can manage it to protect organic matter by leaving enough residue in place, chances are we will have more than enough cover for erosion control. I believe it is possible to take some residue off, but not everywhere.”

The focus in protecting soil has shifted from the mineral component of soil to its organic matter, which is more sensitive, says Johnson. “In most cases, protecting the organic matter will protect against erosion, but if you only manage for erosion control, that may be not enough to retain the organic matter.”

Gone with the wind

The “Black Blizzards” of the 1930s Dust Bowl proved beyond question that wind can transport large amounts of soil to the wrong place. Could we see a rerun of the Dust Bowl? “People say we will never have a Dust Bowl again, because of the conservation practices that we put in,” says Hatfield, but the Dust Bowl also followed years of severe drought, which further stripped farm fields of cover.

Furthermore, says Hatfield, co-editor of a new book on soil management,2 many of the windbreaks planted to slow wind erosion have been removed to allow the use of large farm machinery. “What would happen if, across the Great Plains, we had three or four years with hardly any rainfall? I dare say we would not see the extent of the Dust Bowl, but would our current conservation practices be sufficient? … How much can you expect when the land is naked?”

Confronting drought

The Dust Bowl shocked Americans, but drought is a common problem that has differing consequences. Recent reports show that California’s farm industry did well during the 2007-2009 drought, mainly because large farmers had access to irrigation water. But wheat production in Southwest Kansas is now expected to fall at least 25 percent due to drought. According to Bloomberg News, the state’s wheat crop “has suffered irreversible damage from the country’s driest spring in half a century…”

In places where irrigation is impossible or inadequate, standard soil-conservation techniques, including retaining organic matter in and on the soil, can improve water retention.

ENLARGE

Cities devour farmland

The 80 million people joining the population every year require 3200 square kilometers land for shopping malls, roads, airports and housing. Cruelly, much of that growth occurs in places with productive soil, says Charles Rice, a professor of agronomy at Kansas State University, because big cities typically start out in a region with productive farms. “Chicago is a prime example; the soils in northern Illinois are some of the best in the world, but unfortunately Chicago is growing. I hate to see that valuable productive land paved, built upon. In Asia and Europe, around the world, megacities are consuming land. We need to figure this out, but nobody has.”

Salty soil is worthless soil

A bright idea: reduce tillage, save topsoil

Perhaps the largest success story in protecting soil is the no-till revolution in agriculture. Rather than turning over soil to bury weeds and crop residues, a no-till machine plants directly in the stubble, then controls weeds with herbicide. The process saves diesel fuel and also retains organic matter, says Hatfield, who observes that carbon compounds oxidize rapidly when the soil is disturbed. “We need to protect the soil from within, with more organic matter, and from the external forces, like wind and water.” Sustaining the soil, he says, “Is really about building that organic matter reservoir.”

In 2010, no- or low-till farming occupied at least 20 million hectares each in the United States, Brazil and Argentina, with significant areas in Canada and Australia.

“If you go to South America and talk to producers,” says Hatfield, “they look at conservation practices as the normal accepted practice — if you used a moldboard plow [which turns over the soil and exposes it to erosion] they would probably shoot you! In the last 20 years, they have realized what a precious resources soil is, and to maintain its viability, they have preserved the organic matter.”

But worldwide, no-till occupies only 6 or 7 percent of the 1,500 million hectares under cultivation. “You could call that a success,” says Lal. “But in the places where it is needed most desperately, Africa, Asia, those desperate farmers cannot implement no-till.”

Summing up

Optimism is not a common response to discussions of the world’s degrading soils. Lal says two to three billion hectares already are degraded, but contends that problems related to energy use, global warming and clean water also have strong ties to land degradation.

To take two examples, surface water is easily polluted when it washes off eroded land, and healthy soil stores vast amounts of carbon, slowing global warming. “All these issues are linked with one another, and soil is the common link,” says Lal. “We have the IPCC [Intergovernmental Panel on Climate Change] to address climate change … but soil is addressed by nobody, even though … we cannot address water security, energy, biofuels, global warming, without soil.”

Not to mention the daily problem of putting bread on the table…

But here’s a reason for optimism: The measures that can solve individual problems often can solve multiple problems. Conservation tillage saves water, organic matter, topsoil, even energy. Drip irrigation reduces salinity and saves water and energy. Cover crops raise fertility and reduce erosion.

And, no coincidence, all of these soil-friendly practices also increase yields.

So if you like to eat, the time to think about soil is … now.

“Oxygen from air or water passes directly from their outer cuticle into their blood vessels. Normally, soil has a mix of air and water — about 50 percent of the pore space in soil is air, the rest is water. Oxygen diffuses easily through air, and the soil stays aerobic because oxygen comes in from the surface.”

But after a rain, the soil pores and the worm burrows fill with water. Oxygen diffuses about a thousand times slower through water than through air, she says. “The worms can’t get enough oxygen when the soil is flooded, so they come to the surface to breathe.”

Beats drowning.

But why don’t the little darlings just slither back downstairs when the soil dries out? This is less clear. “Once at the surface, they seem to get confused about where their burrows are,” Balser says. “It may be that cars, lights and people disorient them. They move to seek safety, but sometimes they don’t make it back into the soil when the burrows drain, and it looks to us as if they are committing squirmy suicide.”

It’s not all gloom and doom, however: spring rains are open season for vermiphagia (eating worms).