Switching on to switching off

A simple invention has the potential to change the way we irrigate, from the backyard garden to large horticultural enterprises.

Story David Salt, Photos Frances Mocnik

A water-saving device, originally developed to meet the needs of subsistence farmers in South Africa, could become one of Australia’s most important inventions. Called the FullStop, it simply consists of a plastic funnel with a black pipe stuck in the middle. But what it does is quite complex: it allows the user to irrigate accurately by showing what happens in the root zone when soil is watered.
Inventor Dr Richard Stirzaker, who works at CSIRO Land and Water, has been passionate about growing plants and understanding how water interacts with the soil all his life. This passion permeates through his work and his home. It’s impossible to visit his average-sized suburban backyard in Canberra and not be gobsmacked by the size, range and productivity of his vegetables, vines and trees. And all over his little horticultural kingdom lie a daunting variety of sensors and probes sticking out everywhere, with numerous lines of polypipe carrying water from rainwater tanks, the washing machine, the kitchen and the bathroom.
“Water makes the world go around,” Richard says. “Today you and I will drink two to five litres, we’ll use 50-200L for washing and sanitation, but we’ll eat between 2000 and 5000L because every kilojoule you consume took around a litre to produce back on the farm. Water is an increasingly precious commodity, but very few people know how effectively they’re using water. I’m hoping the FullStop will get lots of people learning about how to deliver the water their plants need – be that a backyard vegetable patch, a market garden or a massive commercial enterprise.”
Richard began developing the device in the 1990s while working with the University of Pretoria in South Africa. He and his team sent out more than 1000 prototypes into a range of irrigated environments, which led to the release of a commercial version in 2004. Almost 10,000 units – at a cost of about $150 for a pair in Australia – have been sold worldwide since then.
According to Richard, the device lets the user know when the soil is full of water, so that watering can be stopped. “It’s what we call a Wetting Front Detector,” he says. “The wetting front is the front line of water as it moves through the soil. It’s like when you add a little water to the top of a dry sponge and watch it move down through the sponge. The wetting front is the line where the wet sponge meets the dry sponge. The soil is just like a sponge. When you're irrigating a crop, it's important to know when that wetting front has reached the main root zone. You don't want the water to go below the root zone because that's simply a waste. And it’s more than just water you’re wasting because you’re potentially losing valuable nutrients carried in that water.”
A funnel is buried in the soil and, as the wetting front moves down into the funnel, it concentrates the water. By the time it reaches the neck or narrow end of the funnel, there’s a little amount of free liquid that flows into a small catchment chamber at the bottom. This causes a float to rise, sending up a flag at the top of the central pipe. “This signal tells the irrigator the soil is full – time to stop,” Richard says.
What really makes the FullStop important is that, over time, it can teach the user how to be more effective with water. “You get a feel for how water is interacting with your soil and your growing system,” Richard says. The water sample in the FullStop can also be used to monitor salt and fertiliser levels.
Joyce Wilkie and Michael Plane from Allsun Farm, a 40-hectare property near Gundaroo in the NSW Southern Tablelands, grow vegetables and market their produce directly to subscription customers and restaurants. “Several years ago we took part in an experiment with the FullStop to see if using it had any impact on our watering behaviour,” Joyce says. “We installed several units and then Richard monitored our water use. The trial ran for three years during which time we planted garlic, pumpkin and carrot crops. Through the trial it became clear that I had been making just about every mistake you could make.”
Joyce and Michael learned that, for sprinklers, the interval they were using between events was too short, and the duration of the irrigation was also too short. So the water was not going very deep into the soil and a lot of it was simply evaporating from the surface. And, for drippers, their interval was too long and the duration of their irrigation was also too long, so the water tended to go below the root zone.
“The thing is that every situation is different, and every person’s experience is different,” Richard says. “It’s not a matter of giving someone a blueprint of how to irrigate perfectly – that blueprint doesn’t exist. However, the FullStop challenges you to question your knowledge every time you use it and that’s how you learn.
“On the very first day when we were setting up and testing the FullStop at Allsun Farm, we were challenged. They’d been watering for less than half an hour and all the FullStops suddenly popped up. They said, ‘What, the water’s gone down that deep in just half an hour?’ And they changed their watering habits from that first day.”
The positive impacts are ongoing. “Besides letting us monitor how the water is moving through the soil, it’s got me interested about the whole topic of water and soil,” Joyce says. “I now think about it every time I turn on the tap.”