Coffee’s Nitrogen Dilemma
The cascading effects of a pandemic, supply chain pressures, and war have skyrocketed the price of nitrogen fertilizer by as much as 300% since 2020. As a result, farmers of all types and sizes worldwide are taking a big hit – none more than coffee farmers.
Coffee farmers operate on razor-thin margins, often selling coffee for less than the price of production. As if that weren’t enough, they are also contending with a changing climate and serious disease and pest pressure.
Unlike other crops, coffee prices have not increased on par with surging fertilizer prices, leaving farmers in an even more precarious position.
Contemporary coffee farming is largely reliant on annual applications of synthetic fertilizers. Without these inputs, many farms lack the soil fertility to produce a crop.
The average rate of nitrogen fertilizers used on coffee farms is comparable to hybrid corn, which is one of the crops with the highest nitrogen demand. Synthetic nitrogen fertilizers applied at these rates produce a plethora of negative effects, many of which compound over time.
Due to the coffee tree’s ecological niche, preferred climate conditions, and physiological traits there is a clear path forward for the successful cultivation of healthy and abundant trees without the use of synthetic nitrogen.
But first, it is important to understand why the move away from synthetic fertilizers in coffee production is imperative, and how it can be done.
Environmental Effects of Intensive Nitrogen Fertilization
When I envision a coffee farm, I see majestic views down the high-altitude rows of emerald green trees. I remember the sweet jasmine smell of a sea of flowering coffee trees, and I feel the enthusiastic buzz of all the work that transforms the fruit of this tree into the magical drink so many love.
What our senses don't capture is that synthetic fertilizers are propping up the productivity of coffee farms. The increase in productivity comes at a high price, both financially and ecologically. The downstream effects of synthetic fertilizer use take farms to the brink of collapse.
People are usually surprised to learn just how much nitrogen fertilizer coffee farms are applying to their soils. What is even more surprising is that up to 64% of the nitrogen fertilizer applied to coffee fields is lost as a result of leaching and volatilization, and the plant takes up only about 25% of the nitrogen. The nitrogen that is leached through the soil profile makes its way into waterways and groundwater, polluting the drinking water of the very same farmers and their surrounding community. As if that weren’t bad enough, these adverse effects continue to compound.
The volatilization of synthetic nitrogen fertilizers contributes nitrous oxide to the atmosphere. Nitrous oxide has an atmospheric warming potential 265 times greater than carbon dioxide. Due to our changing climate, the areas suitable for coffee production are estimated to decrease drastically within the next thirty years. Who would have thought that standard soil fertility practices would be a contributing factor?
One of the unique characteristics of coffee farming is the lack of irrigation infrastructure on most farms outside of Brazil. Coffee trees rely on predictable rainfall cycles to produce a crop of cherries each year. An essential part of what makes this possible is the high soil organic matter in the typical coffee farm soils that serves as a sponge to hold and release water to plants as needed. Each one percent of soil organic matter can store 144,000 liters of water per hectare. Between rain events and during the dry season, coffee trees can access the water stored in the soil through capillary action, the same way water moves up through a straw resting in a glass.
Synthetic nitrogen fertilizers were once thought to contribute to, or at the very least maintain soil organic matter. However, several recent long-term studies show that these fertilizers caused a net decline in soil organic matter even with massive additions of residues (organic matter) to the soil. The implication to soil health as a whole is extreme. But, if we only consider this in terms of the effects on the resilience of coffee trees to drought and extreme weather conditions, it is grim enough.
Another unique characteristic of coffee is its place as one of the few crops compensated based on quality. Under optimal nutritional conditions, the secondary metabolites produced by coffee trees end up in the fruit and seed, thus determining the unique and robust flavor profiles that make each coffee special. The key to creating optimal nutritional conditions is assuring the availability of a broad spectrum of minerals for plant uptake, mediated by a thriving web of soil microorganisms.
The exorbitant rates of synthetic nitrogen used on coffee farms impede the uptake of essential nutrients like calcium, potassium, boron, copper, and several other key mineral nutrients related to coffee quality. Unfortunately, this is not a one-time event. Seasonal applications of synthetic nitrogen acidify the soil, causing lasting soil nutrient imbalances and potentially toxic conditions. The chemistry within plants is also negatively affected. Elevated nitrogen levels in plant sap decrease the concentrations of phenolic compounds and other plant secondary metabolites responsible for creating each coffee’s unique flavor signature. These same flavor-giving compounds are also responsible for imparting immune-boosting qualities to plants that help ward off diseases and pests. The most detrimental impact synthetic fertilizers have on soil is wiping out the beneficial microorganisms responsible for nutrient cycling, building soil structure, and providing immune support to plants.
To the untrained eye, most coffee trees look vibrant and healthy due to the deep green leaves and luscious vegetative growth resulting from high nitrogen fertilizer rates. However, beneath the facade, these trees will have inconsistent fruit formation, sub-optimal flavor, and poor immunity.
Just as coffee stands out as one of the most complex and challenging crops to grow, it stands out for the myriad of creative solutions ready to be employed for the betterment of coffee farmers and consumers alike. All we have to do is start from the ground up.
Biological Coffee Farming
Coffee as an agricultural commodity is unique in that it can grow in the shade of and together with countless other tree species. Coffee trees prefer to grow in these conditions and have evolved to do so. This gives coffee farmers a unique opportunity to produce additional revenue streams alongside their coffee and generate an abundance of fertility from within their farm gates.
In many coffee-growing regions in Central America, trees like Inga (Inga edulis) and Poro (Erythrina poeppigiana) can be spotted from a distance and indicate the presence of coffee trees beneath their shade. Inga and Poró are both members of the Fabaceae family and have the unique ability to convert atmospheric nitrogen into a biologically available form of nitrogen in the soil. This process is called biological nitrogen fixation. Through this process, nitrogen-fixing trees on coffee farms can contribute 60-350 kg/ha of nitrogen from leaf litter and residues and another 30-60 kg/ha of N from fixation in the rhizosphere. This can exceed the recommended rates of synthetic nitrogen (200-250 kg/ha), yet in a more plant-available form that doesn’t leach or volatilize and comes with the added benefit of significantly increased soil organic matter, enhanced nutrient cycling, and water storing capacity. To further propel this biological flywheel, farmers can add perennial nitrogen-fixing ground covers to their systems, adding to the above-listed benefits and offering much-needed soil erosion mitigation.
In order to fully benefit from the wonder of biological nitrogen fixation, farmers need to understand the interplay between soil minerals, the physical structure of the soil, and beneficial soil microorganisms.
Nitrogen-fixing plants form nodules on their roots to host rhizobium, the nitrogen-fixing bacteria that perform the miraculous feat of converting inert atmospheric nitrogen into a plant-available form of nitrogen. When nitrogen fixation occurs in these root nodules, they will be pink to blood-red color inside. When active fixation isn't taking place, the nodules will be a pale grayish color inside. I have been on numerous farms in the tropics where the system's fertility was predicated on nitrogen fixation only to discover inactive root nodules. The reason in almost all cases was a lack of available minerals, namely calcium, copper, cobalt, and iron (some of the same minerals affected by the overuse of nitrogen fertilizers). All save for iron are typically in low supply in tropical soils. The first barrier to clear in optimizing N fixation is to ensure these four minerals are adequately supplied. For beneficial soil microbes, including rhizobium, to function properly, they need to have the appropriate habitat in the soil. By increasing soil organic matter and balancing the soil minerals referred to as base cations, soils become filled with pore space. The pore space acts like a newly developed neighborhood made up of comfortable houses. Upon its construction, multitudes of beneficial microorganisms fill the new houses. They get right to work in the new community, cycling nutrients, defending the plants from disease and continuing to build and enrich the soil.
The exact process for optimizing nitrogen fixation and overall soil nutrient cycling will look different on each farm. Often this will require other inputs like biostimulants, compost, microbial inoculants, organic fertilizers, and mineral amendments to kickstart the system. It’s not a recipe but a set of principles based on plant physiology, mineral nutrition, and soil ecology.
Finca San Jeronimo Miramar (FSJM), a picturesque coffee farm in Guatemala, is a unique and powerful example of the transition from synthetic fertilizer and pesticide dependence to a fully biological method of producing world-class coffee. They have seamlessly integrated a principle-based approach to fit the farm’s operational capacity. The results speak for themselves. At FSJM, Coffee leaf rust infections historically hovered around 20-40%, even while using several chemical fungicides. After four years of no chemical fungicide applications, enhanced plant nutrition, and improved soil microbiome, rust infection rates are now less than 5% across the farm. Over the same four-year period, synthetic fertilizers were eliminated completely Yet, the coffee trees display luxurious growth, even during physiologically taxing periods like flowering and fruit fill. Leaves that once displayed consistent mineral deficiencies now look picture perfect. Most importantly, yields and fruit quality continue to rise, and the surrounding ecosystem is thriving.
The untenable cost of synthetic fertilizers and the drastically declining health and productivity of many coffee farms is the final impetus needed to embrace the possibility of a future of coffee built on healthy soil. Fortunately, coffee trees have a preternatural ability to grow remarkably well and produce abundant and high-quality yields without the need for synthetic nitrogen fertilizers. This is a harbinger of hope for the future of coffee.
