“The days of starting the pump in an orchard and assuming the trees will be watered are long gone,” says Willem Kieviet, area manager of Indigo Fruit Farming on the outskirts of Mbombela, Mpumalanga.
Instead, he uses a meticulous method in which every decision is backed up by data, and any water applications are checked and double-checked.
“You need to think about how much water you’re applying and why. Ask yourself what time of the day is best for irrigating and what the expected outcome of the irrigation is, then measure whether it was achieved. Applications that rely on technology must be followed up by people, and vice versa.”
Indigo produces mandarins and seedless lemons, and has been using drip irrigation since 1997. Kieviet prefers this method to micro-irrigation, as it uses less water.
“With micro-irrigation, there’s more evaporation because you’re wetting a bigger surface area. Also, the water penetration isn’t necessarily as deep as with drip irrigation, so you lose a portion of the water you apply. Drip irrigation is more focused on a specific area.”
As the farms have mostly sandy loam soil, drip irrigation provides a further benefit: the drippers provide a suitable flow of water to top up the moisture levels without run-off.
The irrigation system differs somewhat from orchard to orchard, as new systems have been introduced on the farms since 1997. While some orchards are planted to a single row of trees with double dripper lines, others have double rows of trees with double dripper lines. The water flow also varies, ranging from 0,7ℓ/h to 2,3ℓ/h. The latter is used for single-row lines and provides water at a rate of 4,6m³/ha/h. The 0,7ℓ/h drippers are placed in double rows and provide 2,3m³/ha/h of water.
SLOWING THE FLOW
Kieviet says Indigo is moving towards reduced flow irrigation. The trees still receive the same amount of water overall, but their uptake is far better with lower flow over a longer period.
A booster pump is used for higher-lying blocks to ensure that the water reaches the irrigation system at the desired pressure.
The farm has a dedicated main line for each orchard so that water can be controlled from the pumphouse, rather than through valves in the orchards.
Each block has a dedicated main irrigation line so that the system can be managed from the pumphouse, rather than the orchard. There are also flow and pressure meters on each line to detect problems and accurately measure what is being applied.
The entire system is automated, which enables Kieviet to view all the irrigation applications at a glance, with problem areas showing up in different colours on his computer screen. Controlling the irrigation from the pumphouse on each farm simplifies management, as valves don’t have to be turned on and off in the orchards, which could be affected by human error.
The trees receive between 3 500m³ and 4 500m³/ ha/year of irrigation water. Citrus trees require about 6 500m³/ha/year. Rainfall in the area is about 820mm annually, which complements the scheduled irrigation, but Kieviet points out that not all rain provides effective irrigation.
“For example, it might rain softly for some time. Although this will count towards annual rainfall, it doesn’t really add much water for the trees. Conversely, storms bring a lot of water, but most of it flows away. We estimate that about 50% of the rain we receive is actually effective irrigation.”
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