Improving tunnel production using less water

The nursery is on the canal system in White River and uses additional boreholes to service the nursery. While the water is of a high quality, Ezigro nevertheless sterilises it in a chlorinator. One of the challenges facing the business is the need to improve water-use efficiency.

“Water will become scarce and we have to constantly look at ways to save and recycle water,” stresses Baird. The business has implemented a number of changes in recent years to reduce water use.

“We’ve changed to finer nozzles in our irrigation system. These are pressure-controlled and produce a fine mist spray. This results in better water absorption in the plants and less waste. There are no wide overlaps where water goes over the trays, so the irrigation is more concentrated.”

The tunnels have two irrigation lines: one for clean water, the other for fertigation. On average, the plants receive water at a rate of 2,5ℓ/tray/day. Baird and his team have also changed the growth medium to improve water-use efficiency. Previously, pine bark was used, but the switch to a mixture of coco peat and coir has resulted in a 15% water saving due to this medium’s superior water retention.

The nursery uses approximately 60m³ of coir and peat a week during peak season. The coir is bought from a local company that sources it from Lithuania, while the coco peat is purchased from Mozambique. Although the peat is three times the price of the pine bark, Baird says the added expense is worth it, as it results in better quality seedlings.

“Pine bark is quite a raw product and has variable nutrients and pH levels. It’s inconsistent, whereas coir and peat are consistent. But we have to ensure that the coco peat’s sodium level is not too high, which is often the case due to the salty air in Mozambique. It’s possible to flush it out, but generally we send it back if the salt level is too high,” he says.

The tunnels are covered with 200-micron plastic to allow light in and keep the interiors warm and humid. The climate in White River is ideal for tunnel production as the minimum and maximum temperatures do not reach extremes. “One needs a consistent temperature to produce a quality seedling,” explains Baird. “The climate created in the tunnels is ideal and no additional heating or cooling is necessary. If the temperature exceeds 30°C, we open up the sides to allow airflow. When the temperature drops, we lower the sides again to contain the heat. We strive for 80% humidity.”


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