Cara Eisenpress - - Soil Health

For Coffee Plants, Healthy Soil Is Key

In 2008 and 2009, the Nevado del Huila volcano erupted in southwest Colombia. Not long after, Clarence Cocroft, a soybean, pecan, and black-eyed pea farmer from Mississippi, bought nine hectares of land 120 miles north of the volcano, a plantation near Bogota where several tons of Huila’s ash had reached. Three years later, Cocroft, who is trained in biochemistry, planted coffee trees on the farm.

“I have always been a coffee lover,” Cocroft says. And he decided to try growing coffee in Colombia in part to satisfy his own curiosity about the question of what makes one coffee better than the other one. After a few years of experimenting and learning as he farmed on the Colombian volcanic soil, he found an answer: “It’s the soil and the brand.”

Cocroft is not alone in wanting to grow a better cup for a growing population of coffee lovers. The market for specialty coffee has shot up over the last two decades. In 2017, 40 percent of American adults were drinking specialty coffee, up from 9 percent in 1999, according to National Coffee Drinking Trends, a U.S. National Coffee Association survey. Amidst this demand, many farmers, like Cocroft, have realized that soil has a profound influence on the finished cup of joe.

Many farmers have realized that soil has a profound influence on the finished cup of joe.

The Best Soil for Coffee

In Cocroft’s case, the volcanic soil has seemed almost magical. “Anything you plant there will grow,” he said of the southwest Colombian region where he plants. In fact, the soil is so rich in nutrients, he says, that he uses no fertilizer at all.

This low maintenance is not necessarily typical. Generally, coffee plants have the same needs from soil as most plants. They need the essential nutrients like nitrogen (but not too much), phosphorus, and potassium. Coffee, which traces its origin back to South Sudan and Ethiopia, also needs its soil in high altitude—between 1000 and 2000 feet (300 and 600 meters) for Arabica, which are generally considered to be higher quality and used for specialty coffee. And, climate matters, too, with temperatures ranging ideally between 55°F (about 13°C) and 78°F (about 26°C), according to U.N. Food and Agriculture Organization (FAO). When the temperature is not too hot, photosynthesis occurs more slowly, as does a plant’s metabolism of nutrients.

Interestingly, silica has been an important element for Cocroft's soil, because it reduces the number of pests, he says. Copper, sulfur, and zinc also fend off pests and common coffee diseases.

Researchers have found that slightly acidic soil is most favorable to coffee plants, so it’s important for farmers to monitor the soil to ensure that the low pH isn’t causing aluminum toxicity or shortages of phosphorus, calcium, and magnesium.

In many coffee-growing countries, there are traditional practices around amending the soil with fresh or composted coffee cherries and other byproducts, like coffee pulp. Reusing these parts of the plants help reduce waste from coffee farms, according to the FAO, as well as contributing microbial populations to the soil.

But, there are criticisms of such practices, too. “Then you get ants,” said Cocroft, who actually repurposes his cherries to make wine.

Soil’s Effect on Coffee

Soil has a direct effect on the quality of a cup of coffee in two ways: first, how it handles moisture, and second, the nutrients in the soil, which affect the oily substances and fats in the bean.

Cocroft also found that volcanic soils have a high water-holding capacity. It holds water well so that roots can “open up,” he says.

“The soil holds the nutrients for the root,” explained Cocroft. “The root has to swell, because if roots are too thin, you have to keep watering, and that destroys the affinity of the coffee, the smoothness.”

Volcanic ash in soil helps swell the roots, he said, so that even though they’re only about a foot long, they swell as big as a finger. Once swollen, the roots retain water. “That limits you from having to water so much,” he said, leading to smoother coffee.

Volcanic soil is good for this kind of water retention, as are soils with high quantities of organic matter.

Soil Trumps Climate

Proper soil management has not always been there in coffee-growing countries, many of which are impoverished and lack guidance from institutions like extension programs, according to Luis Álvarez Welchez, who worked for decades with the FAO. Small coffee growers often sell to much larger traders, a system that also doesn’t encourage slow-and-steady soil health management.

For Cocroft, soil health truly transcends the importance of either climate or altitude, and he has an experiment under way to prove that. With a pilot study at Mississippi State, Cocroft is bringing volcanic ash soil to greenhouses in his home state and planting coffee there. The program intends to control most variables by using smart greenhouses, AKA growth chambers. “We’ll make the same humidity, atmosphere, and pressure as Colombia, just indoors,” he said. But the magic soil? That needs to come from Colombia.