Coffee husks are a big potential risk to soil nutrients due to high carbon in them.
By Arnest Tumwesige
LUWERO: Luwero District, home to more than 140 coffee hulling machines most concentrated in the town council is grappling with a growing paradox: the rapid rise in coffee production is generating massive volumes of husks that are both a potential economic resource and an emerging environmental concern.
With an estimated annual output of 800,000 bags of coffee, each weighing 60 kilograms, the district produces thousands of tonnes of coffee husks every season. For many farmers, these husks have become a readily available solution for mulching. But agricultural experts warn that this common practice could be silently degrading soil health.
According to Wilberforce Semigga, the District Principal Agricultural Officer, the problem lies in the high carbon content of coffee husks. For such materials to decompose into beneficial organic matter, they must undergo a biological process driven by microorganisms one governed by the Carbon-to-Nitrogen ratio.
“The breakdown of carbon into simpler, biodegradable substances requires a lot of nitrogen,” Semigga explains. “This creates competition between soil microorganisms and crops for nitrogen, which is essential for plant growth.”
Research shows that materials with a high carbon-to-nitrogen ratio, such as coffee husks, can trigger nitrogen immobilization a process where nitrogen becomes temporarily unavailable to plants. Instead of enriching the soil, the husks may initially deprive crops of vital nutrients.
While farmers may observe short-term benefits such as moisture retention and weed suppression, the long-term effects could include declining soil fertility.
“If left untreated, the husks behave almost like a nutrient sink,” Semigga adds. “They absorb nitrogen that crops would otherwise use.”
Tapping into the potential
Within this challenge lies a significant economic opportunity. Studies show that when properly processed through composting, co-composting with nitrogen-rich materials like animal manure, or conversion into biochar coffee husks can be transformed into high-quality organic fertilizer and soil enhancers.
This opens up new possibilities for agro-processing enterprises focused on organic fertilizer production; establishment of composting facilities for sustainable agricultural waste management; and bioenergy generation and alternative uses such as animal bedding and feed additives
Globally, major coffee-producing countries such as Brazil and Vietnam have already embraced coffee waste valorization turning husks into bioenergy, organic inputs, and other value-added products. For Luwero, this presents an untapped agribusiness frontier.
Evident practice
At the farm level, however, traditional practices persist. Naluggo Margaret, manager of a coffee hulling facility in Kasana Industrial Area, notes that about 80 percent of farmers who bring their coffee for processing take back the husks.
“Some private individual buy husks that remain at the factory is a bags, but most prefer to reuse what comes from their own coffee,” she says.
Paul Mugerwa, a coffee farmer from Lumu Zone in Luwero Town Council who has been in the trade for seven years, says husks are central to his farming routine.
“I use them for mulching my coffee garden and as litter in my poultry house,” Mugerwa explains. “In areas where husks are applied, weeds don’t grow easily, which helps with weed control.”
However, he admits uncertainty about their long-term impact on soil fertility.
“If it is true that the husks reduce soil nutrients, then experts need to come and guide us. Otherwise, we could be damaging our soils without knowing,” he says.
The economic incentives for coffee farming remain strong. A kilogram of kiboko (unshelled coffee) currently sells for about UGX 7,000, while fairly average quality coffee fetches up to UGX 15,000 after hulling encouraging farmers to increase production and, consequently, husk generation.
Nakasongola, Nakaseke focus
Across the greater Luwero sub-region, including Nakasongola and Nakaseke districts, coffee is increasingly becoming a dominant cash crop. In Nakasongola, agricultural officer Henry Kawesi notes that coffee thrives particularly in the wetter sub-counties such as Kakonge, Kalongo and Katungo.
Meanwhile, the Buruuli Cultural Institution in Nakasongola has launched an initiative targeting the planting of 100,000 coffee seedlings among at least 500 farmers, further boosting production prospects.
In Nakaseke District, agricultural officer Rwela Titus says coffee is central to household incomes, with expansion efforts being supported under the Parish Development Model. As coffee production expands, so too does the urgency to manage its by-products sustainably.
