Aquaponic farming turns fish waste into cheap organic fertiliser

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Former university students are helping farmers in establishing pond water recycling units which allow for utilisation of fish waste as crops feriliser as one of the ways of reducing chemical nutrient supplements.

The aim of Vintage Greens Limited, which is owned by 18 Jomo Kenyatta University of Agriculture and Technology’s alumni, is to help agripreneours cut production costs for increased profit margins through aquaponic farming.

Integrated or aquaponic farming involves turning fish metabolic wastes into nutrients for crops. As the crops mint out the nutrients for growth, they purify the water for the fish.

Vintage Chief Executive Officer Elijah Njoroge said organic farming is one of the major solutions of beating stringent chemical residues in horticultural crops for export to markets like the European Union.

Horticultural crops entering the EU must not have chemical residue of more than 0.02 chemical parts per million.  Inorganic fertilisers and other agrochemicals account for increased residues in produce.

In their set-up, the company grows strawberries together with fish.  Strawberries are grown in a soilless culture such as pumice or cocopit growing which is filled in vertical or horizontal perforated tubes.

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Soil is not used in the set up because it turns the water into mud.

The water is pumped out of the pond to irrigate the crops, which also extract urea and other fish metabolic wastes for growth.

“Urea is rich in nitrogen. Remnant food particles also have nitrogen as well as potassium and phosphorus. Strawberries are heavy nitrogen feeders, therefore, the urea is absorbed. In the process of passing through the soilless media, the water is aerated too before flowing back into the pond,” Njoroge said.

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Accumulation of urea in the pond and decomposition of the excess feeds can poison the fish, causing death.

The solid particles can also clog the gills of the fish, hence, reducing respiration, which may lead to suffocation.

The system is self-sustaining, therefore, no need of adding chemical fertilisers to the green garden.

READ ALSO:Prisons officer helps farmers set up integrated backyard fishponds

Depending on the size of the ponds a farmer requires, Vintage determines the population of the strawberries to be grown to sustain the agribusiness.

Strawberry fruits and fish mature in four and six months respectively. 

PHOTO: Strawberries grown in an aquaponic set-up. JKUAT alumni are helping farmers establish aquaponic farms. PHOTO BY YOUTUBE

Njoroge can be reached on +254706808633