The ideal cup of coffee for the morning. Many things must go right before that great-tasting coffee can be poured into your favourite mug, even before you buy the beans at the supermarket. It all begins in the earth, where the beans are grown. Brazil, for example, is the world’s largest coffee producer, yet its soils can be challenging for coffee plants.
Coffee grows in tropical soils that are inherently acidic and deficient in calcium and magnesium. Furthermore, adding fertiliser to the soil increases its acidity. All of these translates to poorer coffee plant yields.
Rogério P. Soratto is a Brazilian researcher who is investigating if limestone and phosphogypsum might assist improve soil. Soratto and colleagues recently published their findings in the American Society of Agronomy’s Agronomy Journal.
Soratto explains that “soil acidity and low exchangeable calcium and magnesium concentrations are among the key factors that limit coffee yield.” “As a result, we conducted a field experiment to assess the impact of limestone and phosphogypsum banding. We looked at them separately and in combination to determine how they affected plant nutrition, yield, and profit.”
Researchers employed various amounts and combinations of just limestone, just phosphogypsum, and the two together in the investigation. Each had a different effect on the soil chemistry. They administered the treatments as a band beneath the plant canopy, at the base of the coffee bushes.
Calcium and magnesium are found in limestone. Its effectiveness is frequently restricted to the soil surface where it is applied. Calcium and sulphur are found in phosphogypsum. It has a stronger ability to absorb calcium into the soil. However, the researchers discovered that combining the two treatments was not as simple as they had hoped.
“The combined application of limestone and phosphogypsum considerably raised the calcium concentration in the soil in our study, as well as causing an overall unbalance of the soil chemistry,” Soratto explains. “This could have limited potassium uptake by coffee plants during the fruit-filling period, when it was most needed.”
In the end, their research determined that using simply limestone was the most effective treatment. Low phosphogypsum rates are recommended if the subsoil acidity is an issue. This will prevent the soil chemistry from being thrown off.
Limestone reduces acidity in the soil while also providing calcium and magnesium. It also reduces the levels of harmful aluminium and manganese in the soil. This boosts the activity of beneficial soil bacteria. Finally, it improves the efficiency of fertiliser. This improves crop performance and makes them more economically feasible.
“The environment in southeastern Brazil is ideal for the growth of Arabica coffee trees,” he explains. “It may make it possible for growers to harvest fruits of high drinking quality. However, because most soils in this region are acidic, this is only achievable in well-managed crops.”
Most notably, the best-performing limestone application raised both coffee yields and economic returns by more than 40%.