Using rocks to grow vegetables

By Gerald Tenywa

The Biblical story of a wise man who built his house on a rock comes to mind when at the residence of Maria Mabira of Mugwanya zone on Rubaga hill, Kampala.

Although her home is located on a rocky and hilly terrain, she has made great gains in agriculture courtesy of modern farming methods. Mabira breeds fish and cultivates vegetables.

Both enterprises thrive in a symbiotic relationship where the vegetables depend on their (fish) waste for survival, a term called aquaponics.

“The venture takes little space, yet the returns are good,” says Mabira (seen below with Charles Mulamata, who is Mabira's partner in the new vegetable growing venture at Rubaga.)

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How does she grow vegetables on rocks?

When Mabira was growing up, she thought plants would die without soil, but has since learnt that crops need just water and certain nutrients to survive.

Aquaponic farmers rear the fish in a tank and as they feed, they release nutrients (urine and faecal matter) into the water. This water is directed to the vegetables in wooden troughs, which contain stone pebbles.

The troughs are lined with polythene sheets to trap the water, which is filtered by the stone pebbles. The water is then pumped back to the fish tank.

Edith Nankya, a manager at Africa Aquaponics, which brings together aquaponic farmers in the country, says such technology can even be used on rooftops.

“This technology solves space issues that have for long plagued urban farmers,” she says.

In addition to this, the technology produces 100% organic products. It also uses less water than other agricultural technologies.

Return on investment

Under a greenhouse, this technology requires sh3.2m. However, each month, a farmer who grows high-value vegetables such as lettuce can earn sh1.8m from the vegetables. After six months, fish such as cat and tilapia can also fetch as much as sh900,000.

“The vegetables help the farmers earn money to buy feeds for the fish,” says Charles Mulamata, the chairperson of Africa Aquaponics.

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Mulamata’s award provides seed money

Mulamata, the brain behind the aquaponics, was recently awarded for his innovation. He has turned part of the prize money into a seed fund to promote the technology.

As a way of creating sustainability, Mulamata has partnered with Mabira to establish a new model that ensures that finances remain available until the project takes off.

On top of this, technical managers adept in fish technology have been employed at Mulamata’s farm.

Mulamata has a hatchery for tilapia and catfish, as well as vegetables such as tomatoes.