Spend on technology, save on water

Gamtoos Valley’s three-year drought meant farmers were only allocated 40% of their annual water quota this year. And the catchment area of the Kouga Dam got little relief, despite recent good rains.

But the valley’s farmers took the initiative and implemented a water-saving system, recording savings of up to 40%. Lourens Schoeman reports.

The Gamtoos Valley, known
as the Eastern Cape’s vegetable and fruit basket, has been crippled by drought for three years. To save water, farmers here have spent over R300 million on sophisticated soil-moisture probe technology – and it’s paying off.About 65 of the valley’s 200 farmers are already participating in the programme, with about 4 000ha out of the area’s total 9 000ha involved.

So far, between 300 and 400 probes have been installed, and the technology’s use in the valley is steadily expanding. The huge cost hasn’t been in vain – water savings of between 30% and 40% have been recorded at a time when the valley’s water source, the Kouga Dam, was at 33% of its capacity, with about 23% of this earmarked for use by the Nelson Mandela Bay Metropolitan Area.

How the probes work
Wouter Vermaak of the agricultural technology company Retouw Landbou, based in Hankey in the Gamtoos Valley, explains that the probes, developed by DFM Software Solutions, are inserted in a grid pattern into the orchard soil to a depth of about 800mm.

These probes simultaneously record soil-moisture content and temperature readings at six depths (20cm, 30cm, 40cm, 60cm and 80cm below the surface), as well as the surface temperature, on a sampling spacing determined by the soil type, its uniformity and water retention capacity and the crop’s requirements. “These values are recorded hourly by a default setting that can also be user-customised.

On this default interval setting, the probe can store up to 4 000 values, or about 22 weeks’ data,” Wouter says.

This soil-moisture management tool takes the guesswork out of irrigation planning. The technology is very expensive, especially for an individual farmer, but it’s impossible to produce optimally without it, as it identifies and treats the cause of suboptimal irrigation, he says.

The probes guarantee accuracy and reliability, are temperature-compensated and aren’t affected by salinity.
Data is downloaded and processed by DFM Probe Schedule Software, a user-friendly package that provides abundant information for effective scheduling.

A DFM Probe Utilities software package interprets soil-moisture content and temperatures – which are continuously recorded by the logging soil-moisture probes – and uses the information to support and implement informed irrigation decisions. It depicts the information on a selection of graphs, including depth, level and summary, so you can see how moisture moves through the soil profile.

Each sensor level can also be viewed independently to determine soil-moisture depth at that spot, how long the irrigation cycle should last, and when to start the next cycle.

“I read the graphs every morning to determine if, and how much water farmers must give their trees or vegetables during the next 24 hours,” Wouter explains. “Some farmers read their own graphs and make the necessary adjustments to their micro-irrigation systems as and when required.

“The system supports decisions that prevent over-irrigation and under-irrigation, promote root development, create the ideal air/water balance and prevent unnecessary crop stress. These decisions also optimise fertiliser intake and salinity management, while saving on energy costs, facilitating crop manipulation and managing the soil/water buffer.”

Saving water, electricity and jobs
Gamtoos Irrigation Board chairperson Merwe du Preez points out that with the new technology, farmers can irrigate, with the same amount of water, about 25% more land now than they did in the 1960s when flood irrigation was used. Pierre Joubert, the Board’s general manager, reiterates, “Water from the dam supplied to the farmers is accurately measured, but the new technology enables farmers to harvest a larger crop using less water.

Every drop a farmer saves is a drop remaining in the dam for the next water year.” Merwe also says that giving trees the right amount of water “is the difference between harvesting export-quality and poor-quality fruit, and between good prices and poor prices. “Furthermore, farmers also find that, with more efficient water use, their electricity bills are now lower than they were before Eskom’s latest price increase.”

The valley’s farmers’ annual quota for the current water year is only 40% of their normal allocation, and Pierre says that every 10% decrease in the quota can lead to 1 000 jobs being lost. Currently 7 000 workers are employed on farms in Gamtoos.

“If farmers hadn’t approached this water year as positively as they did by continuing normally in the belief that it would rain before the dam dried up, and that restrictions would eventually be lifted, thousands of people would already have been out of work. In Gamtoos, water brings jobs and food.”

Although farmers are positive and say the situation could have been far worse if they hadn’t adopted the new technology when they did, they’re upset about facing the brunt of restrictions while “real restrictions” aren’t in force in Nelson Mandela Bay.

Merwe says, “The restrictions in Nelson Mandela Bay are such that consumers only pay more for their water if they use more than a certain amount. But when we’ve used our quota, our sluice gates are closed.” He says they’re also unhappy that the Nelson Mandela Bay Municipality only reacted to restrictions months after farmers did.