“Do you know how the traditional paraffin lamp works?” This is the question Prof John Wesonga, an Associate Professor in the department of Horticulture at Jomo Kenyatta University of Agriculture and Technology (JKUAT) poses as he leads the way to one of the greenhouses at the research site.
My mind draws memories of the small sooty lamp made from a metallic bottle with a piece of cloth dipped in paraffin and acted as the wick. The other end of the piece of cloth was lit into a flame to provide light. But what does this have to do with plants and their water requirements?
“This is exactly how the capillary technology works on irrigated farms. Water from a reservoir is led to the plants along the wick and through the growth medium to provide the exact water requirements for the crop,” explains Prof Wesonga.
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Inside the greenhouse there are tomato plants neatly organised according to their growth stages. There are fruiting ones as well as those heavily weighed down by near-ripening tomatoes. There are younger plants too, their succulent dark leaves hanging firmly on stems that shoot from different kinds of potted growth media.
Unlike other greenhouses at the university with manifest irrigation systems of interconnected piped water, there is no clear indication of how the healthy-looking crops are watered.
But tucked beneath the potted plants are gutters that supply each row of plants with water. And bulging from beneath each of the potted media are wicks dipped into the gutters to suck and transport water into the soil, cocopeat and other types of growth media.
Capillary action
Prof Wesonga explains that the technology works on the concept of capillary action where water from the reservoir is led along a wicking rope upwards to the soil.
“The technology works the same way paraffin is led up the wick in a lamp to continue burning and providing light. Similarly, water is led up the wick to the growth media to keep the plants irrigated. In this model, irrigation is not done above the crops but directly to the roots,” says Prof Wesonga, the project lead researcher.
He conceived the idea to localise the capillary wick technology while he tested production of sweet melons using a similar technology at Okayama University in Japan. That was in 2007.
Wesonga says the target of the technology are urban dwellers with an interest in soilless and stress-free farming.
His idea is also to come up with a system that minimises wastage of water where crops are able to take only what they require.
“With the changing climatic conditions, less rainfall and its unpredictability, there is increasing need to leverage on technology for systems that consume as little water as possible,” he says.
He says the Africa ai (Africa Innovation) Japan funded project is the easiest form of irrigation technology since it doesn’t need any pumping system, electricity or any form of power.
The technology which is still under review has also been found to consume far much less water compared to the normal watering from the top.
No minerals lost
According to Martin Mburu, a graduate in the School of Agriculture and Natural Resources at the university, who is also part of the team of researchers working on the project, up to 63 per cent of water was saved on the crops within a period of six months in the greenhouse.
“When you water from the top, the crops take in only what they need and the rest is lost through surface run-off. But when the irrigation is done from the bottom, no water drains away,” says Mr Mburu.
The graduate researcher explains that soil particles have pores in which water is held to be taken in by the roots while any excess water runs through and is wasted away. He further divulges on the ease of installing the irrigation technology, saying it can be assembled from locally available resources.
Running water also causes another challenge that can be avoided by capillary wick. According to the researchers, surface run-off takes with it a lot of soil nutrients and fertilisers and the excess farm chemicals further results in environmental pollution.
The technology requires little planting media and is therefore suited for urban farmers, some who buy soil to grow vegetables in their backyards.
The fact that the roots are left to take in the water they need further eliminates the need for human input and supervision, making it even more appealing to farmers who have other engagements.
The best part, perhaps, is the ease of construction of the structure which uses locally available materials, making it affordable to small scale farmers.
Affordable materials
A system that holds 28 plants, for instance, needs only Sh5,000 spent on water collection gutters, timber to make a structure that holds the gutters together and wicking ropes which are industrially produced to make suits.
The researchers say to achieve maximum results and minimise water loses, however, the distance of between the wick and the water reservoir should not be more than 4cm.
Common in Japan
“The distance should be very short to ensure the wicking system is not exposed to the environment too much. The more the wick is exposed, the more water it loses to the atmosphere through evaporation,” says Wesonga.
At a more advanced level, the technology is usually a complete automated system that is connected to an even larger reservoir that supplies the gutters with water to be led through the wicks. The large tank has a float valve to automatically refill when the water levels fall.
According to Wesonga, the capillary wick technology is well-established practised in Japan and other industrialised countries.
Instead of the gutters and pots used in research at JKUAT, farmers in Japan use a self-contained unit with a base that acts as a water reservoir and a section for the growth medium on the top base of the reservoir. The wick used in Japan is well covered to prevent growth of roots along its surface.
“Roots tend to grow towards the water source and that’s why they grow along the wick. This sometimes interferes with the capillary action thus the need to cover the wicking system properly. But locally, we don’t have proper wicking ropes,” Wesonga adds.
