By Antynet Ford

Vegetable farmer Zahra Ahmedis facing an increasingly fierce cycle of destruction to her drip irrigation system as water salinity rises around her farm in Bombo, Bamburi, clogging and destroying her system’s pipes.

Over 94 percent of groundwater in the north coast aquifer is above the World Health Organisation’s safe levels for salt, while around 42 percent is fully saline during dry seasons. Yet too much salt quickly poisons crops.

At the lowest levels of coastal groundwater salinity, sensitive crops, such as beans and onions, suffer yield declines and reduced vegetative growth. But at common coastal levels, yield losses reach 25 to 50 per cent for almost all staple and horticultural crops, including maize, beans and tomatoes, rising to 75 per cent at the region’s top sale levels, at which point most crops are ruined.

This has limited the volume of tomatoes Zahra grows, which are particularly hard hit by salts. “On large scale, I farm cowpeas (mkunde), amaranth (mchicha), and okra (mabenda) and tomatoes, I do on small scale and sell to people in my estate where I live,” she said.

But the salt levels are also blighting her irrigation system, by scaling up the pipes and emitters, reducing water flows, watering unevenly and eventually clogging.

“The truth is that irrigation here is really hard… the pipes get blocked every time and you have to keep on changing them because it gets to a point when they are completely blocked and no water can pass,” said Zahra.

“I clean them twice or thrice then when the blockage is beyond repair, then I replace them and the process continues.”.

“This is very costly for a smallholder farmer like me, especially because, you see, the pipes are bought with money. But I realised the green ones last a bit longer than the black ones, so, nowadays I will always buy the green pipes.”

“But at the end of it all, they also get clogged by the salty water.”

Irrigation engineers report that adding nitric acid or other acids to irrigation water until the water reaches a pH of 5.5 to 6.5 dissolves the scale inside pipes. But this needs careful managing to stop the soil acidity rising too high for healthy plants.

Another way to extend the pipe life is to flush water through the pipes at speed to wash our some of the deposits.