Treated cocopeat–pumice mixtures influence substrate physico-chemical properties, nutrient uptake and potato yield (Solanum tuberosum L.)

Potatoes are a global staple, feeding billions and serving as a critical pillar of food security in many nations. Yet, for farmers in places like Kenya, growing this crop is a constant struggle against the soil itself. Traditional fields often harbor invisible enemies: bacteria, fungi, and nematodes that infect the seed and destroy the harvest. To escape these soil-borne diseases, agricultural scientists have turned to soilless culture, a method where plants grow in a clean, artificial medium rather than dirt. Among the materials used for this, cocopeat—a fibrous byproduct of coconut husks—has become a gold standard. It holds water well, lets air reach the roots, and supports healthy growth. However, cocopeat is expensive and difficult to source in regions far from the coast, creating a barrier for many farmers who need affordable ways to produce disease-free seed potatoes.

This economic reality led researchers to ask a practical question: can they mix cocopeat with a cheaper, locally available material to get the same results? Pumice, a lightweight volcanic rock with a sponge-like structure, offers a promising alternative. It is abundant in Kenya and known for improving drainage and aeration in soil. The challenge was to find the right balance. If the mix contains too much rock, the plant might dry out; too much cocopeat, and the cost remains high. A team of scientists set out to test various combinations of these two materials to see if they could replicate the success of pure cocopeat while lowering the price tag for potato farmers.

The researchers conducted their experiment inside a greenhouse at Egerton University in Kenya, using a popular potato variety known as Shangi. They prepared five different growing environments to compare against each other. The first was pure cocopeat, the second was a mix of seventy-five percent cocopeat and twenty-five percent pumice, the third was an equal fifty-fifty blend, and the fourth was a mix with only twenty-five percent cocopeat and seventy-five percent pumice. The final group served as a control, using standard field soil to show how the plants would perform in traditional conditions. Each setup was repeated three times to ensure the results were reliable, and every plant received the same careful watering and nutrient feeding through a drip irrigation system.

Before the potatoes even began to grow, the team measured the physical nature of these different mixes. They looked at how much water each material could hold, how much air was trapped inside the pores, and how heavy the material was for its size. The results showed that the control soil retained the most water of all (52.0%), while the cocopeat blends generally held more moisture than the pumice-heavy mixes. The pure soil control was also the heaviest and had the lowest air-filled porosity, meaning it offered the least amount of air space for roots to breathe compared to the lighter, more porous cocopeat and pumice blends. The blends of cocopeat and pumice struck a middle ground, offering a balance of moisture and air that is crucial for root health.

When the researchers checked how well the plants absorbed nutrients, they found that the blends performed exceptionally well. The plants growing in the fifty-fifty and twenty-five-seventy mixes absorbed significantly more nitrogen, calcium, and potassium than those in pure cocopeat. This suggests that the presence of pumice helped the roots access these vital nutrients more effectively. The plants themselves responded with vigor. The ones growing in pure cocopeat grew the tallest, reaching nearly sixty-eight centimeters, but the fifty-fifty blend was a very close second. These plants also developed more branches and maintained a greener, healthier canopy for longer than those in the soil or pure pumice. The greenness of the leaves, measured by a device that detects how much light the plants reflect, remained high in the cocopeat-rich mixes, indicating strong photosynthesis and robust growth.

The ultimate test, however, was the harvest. The goal was to produce minitubers, which are small seed potatoes used to start new crops. The pure cocopeat treatment produced the highest yield, with each plant generating about four hundred and two grams of tubers. The seventy-five-twenty-five blend followed closely with three hundred and seventy-five grams, and the fifty-fifty blend produced three hundred and seventy-two grams. These three treatments were far superior to the pure pumice and the soil control, which produced significantly fewer and smaller tubers. The data revealed a clear pattern: the soilless mixes dominated in producing the small, uniform tubers needed for seed multiplication, while the traditional soil produced fewer but larger tubers better suited for the food market.

The study concludes that while pure cocopeat remains the top performer for maximizing potato seed production in a greenhouse, it is not the only viable option. The fifty-fifty blend of cocopeat and pumice performed nearly as well as the pure material, offering a substantial reduction in cost without sacrificing yield. This finding provides a practical solution for farmers who need to produce high-quality seed potatoes but cannot afford to rely solely on expensive imported media. By mixing local volcanic rock with coconut fiber, it is possible to create a growing environment that is both affordable and highly effective, helping to secure the potato supply chain against the diseases that plague traditional farming.