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February 08, 2009

Poor attention to drainage threatens Tanzania irrigation project

Sophia Shimbo was among the pioneers of a government settlement scheme in Kivulini, Mwanga District of northern Tanzania in the 1970s.

The once successful agricultural project, which made a semi-desert bloom with maize, rice, and vegetables, is now moribund. The desert has reclaimed its own, due to lack of foresight by official planners.

With abundant supply of water from rivers flowing from Mt Kilimanjaro and nearby springs, what was once arid land was turned into rice fields, maize and beans farms through irrigation. By all standards, the yields were good and excitement was high as many farmers in Tanzania joined the irrigation scheme.

However, the designers of the irrigation scheme overlooked one critical factor — drainage — in the design of the irrigation systems. Because of the poor drainage, salts started to accumulate in the soil. By 1980, many farmers were reporting salt deposits in their fields.

Studies done in the area by the Agricultural Research Institute (Ari-Mlingano) in the 1992 established that soil salinity had affected 65 per cent of the 410-hectare irrigation scheme with disastrous effects on crop yields.

Maize yields dropped from 1,400 kg to 600 kg per hectare and it became almost impossible to grow beans, tomatoes and water melon in the saline soil. Yields of the three crops dropped by half from 1,000, 3,800 and 9,600 kg per hectare respectively, according to Abdul Karim Munisi, Kileo Ward Agricultural Extension officer.

Ms Shimbo recalls that she could only average seven bags of rice from her one hectare farm, down from an average of 40 bags when she started in 1974.

Concerned about the decline, Ari-Mlingano approached the Kenya-based Maendeleo Agricultural Technology Fund — an initiative managed by Farm-Africa — to partner with it in reclaiming the salt-affected area. With financial support from the Fund, Ari-Mlingano embarked on the project in partnership with a sister research institute — the Arusha-based Selian Agricultural Institute — to introduce technology that would reverse the salinity in the soil.

The technology, which combined the use of gypsum (calcium sulphate) — a naturally occurring white mineral — as well as drainage and good irrigation techniques, had demonstrated ability to reclaim salt affected areas in previous studies.

This time round, Ari-Mlingano ensured that drainage was part and parcel of the new technology.

Charles Lyamchai, principal agricultural research officer at Selian Agricultural Research Institute, singled out the importance of drainage as a critical factor in the reclamation of the salt affected area.

He said the use of gypsum helps break down sodium bicarbonate to form calcium bicarbonate — which is not harmful to plants — and sodium sulphate, a compound that dissolves easily in water and drains away through the drainage canals.

Indeed, farmers who apply gypsum without a proper drainage system will not solve the problem, as Mwanganga Juma found out. He continued harvesting a bag of beans from his half hectare irrigated field in Kivulini while those combining gypsum and good drainage had yields of up to 35 bags from a similar piece of land.

Ms Shimbo has seen her yields rise from 30 bags of rice in 2006 to 60 bags in 2007 from her one hectare plot.

Mohamed Juma, chairman of Kivulini Water Users Association, has seen the productivity from his half-acre paddy field in Kivulini rise from only 12 bags before application of gypsum to 28 bags of rice after reclamation. He hopes to attain 35 bags after completing the reclamation.

On the flip side, the price of gypsum has been rising steadily from the initial Tsh20,000 ($18) to Tsh35,000 ($31) per 90 kg bag.

So far, half of the 410-hectare scheme has been reclaimed.

More farmers are taking up the technology because they can see the benefits.

But across the border in Kenya, the technology has not been adapted.

This is because, unlike in Tanzania, the area has not been transformed into an irrigation scheme, despite the abundant waters flowing from the nearby springs and rivers from Mt Kilimanjaro.

The East African

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