By helping farmers measure soil moisture with precision, a simple sensor is reducing waste, improving yields, and making agriculture more sustainable.

RANDFONTEIN, South Africa –

Patricia Seaba faced many challenges when she began farming. But few were as perplexing as the exploding cabbages. One moment, the plants seemed fine, cocooned snugly in their leaves, growing into the swirly purple and white heads that customers in suburban grocery stores couldn’t get enough of. The next, she was sitting in her living room when she heard a pop outside. When she got to the field, the cabbages “were bursting like balloons,” Seaba recalls. 

The problem continued for the rest of the season. Not every cabbage she grew self-detonated, but enough of them did that it eventually stopped surprising her. Sometimes, Seaba says, she would pick a cabbage intact, only to have its rubbery body split apart in her hands. 

Seaba knew that the plants she grew were always communicating with her. As she tended the fields of her 17.5-hectare (43 acre) vegetable farm near Johannesburg, she watched their color, texture, and posture for clues about what they needed. But exploding cabbages were like a foreign film with no subtitles. They must be trying to tell her something. She just had no idea what. 

The answer, when it arrived, was unexpected. And it came from an equally unforeseen source. One day in 2023, a government liaison for farmers visited Seaba. He had a small device in his hand, made up of three wires, each with a small white water-sensing bulb dangling from it. The man explained that this was a Chameleon. It had been developed by an organization called the Virtual Irrigation Academy (VIA) to tell farmers like Seaba how much moisture was in their soil. That, in turn, would help them make better decisions about watering their crops. 

Seaba was skeptical. After all, she could see with her own eyes when the red dirt at her feet was cracked and dry, indicating the roots coiled below the surface needed water. Anyway, she and her partner Rinae Tshikangavhadzi irrigated their fields the same way all their neighbors did—three times a day, every day. Why reinvent the wheel? 

Still, they decided to give the little device a try. And almost immediately, the Chameleon returned a surprising message. “We saw we were giving all the plants too much water,” she recalls. 

This, it turns out, is what the exploding cabbages had been trying to tell her. They were drowning. 

Turning Water Into Food 

VIA’s Founder Richard Stirzaker has been talking to plants most of his life. Long before he was a research scientist with a specialty in irrigation and an obsession with what he calls “turning water into food,” he was a little boy growing vegetables in the sandy soil of his Cape Town backyard. 

When he was in kindergarten, his teacher asked him to bring a seed to school and plant it. “I couldn’t believe that thing made a bean,” he recalls. “I thought, this is magic.” 

Stirzaker never fully recovered from that wonder. Instead, he turned it into a career. When he was a teenager, his family moved to Australia, where he pursued his PhD in soil physics. Then he went to work studying agriculture for the country’s national science organization, CSIRO. 

Over time, he became obsessed with one particular problem: Water. 

Stirzaker often worked with smallholder farmers in sub-Saharan Africa. And every one he met grappled with the same quandary: how much water was needed for their plants to grow. 

To be clear, the technology to solve the problem existed. The 5 percenters of global agriculture, large commercial farms, were outfitted with an expensive array of devices to measure the moisture, temperature, and nutrient content of their soil. As a result, they could gauge with precision when to water, and equally crucially, when to stop. 

But more than half the world’s food is grown on farms less than 50 hectares (123 acres) in size. A third is grown on farms smaller than 2 hectares (5 acres). And Stirzaker knew that when it came to gauging water use, smallholder farmers had almost nothing to go on but what they saw with their own eyes. 

And as it turned out, their eyes were deceiving them. 

The conventional wisdom tended to go like this: Irrigate your crops when the soil looks dry. And yes, dry soil sometimes means dry, thirsty plants. But it can also just as easily indicate that the ground is protecting itself, forming that crusty exterior to shield the moisture below from evaporation. 

However, short of digging up their own fields every time they watered them, farmers had no way to see what was happening down in the root zone. And because the dangers of too little water were so clear, they often ended up swinging too far in the other direction. They “killed their plants with kindness,” explains Luan Steyn, VIA’s Research and Development Engineer. Kindness, that is, in the form of too much water. 

Overwatering, it turns out, is all kinds of bad for farms. It flushes nutrients from the soil, which must be replaced—often at great expense—with fertilizer. Plants yield less. And that’s to say nothing of the social implications. Water is a shared resource, and in many parts of the world, farmers compete for their share of communal sources, cutting rifts through communities and families. 

Closing the Knowledge Gap 

For Seaba and Tshikangavhadzi, the exploding cabbages proved only the tip of the iceberg. They irrigated all their crops three times a day, just as they saw the other farmers in the area do. But all that irrigation meant that they had to keep their small pump running day and night to transport water from a nearby dam to the fields. Huge electricity bills chewed away at the farm’s small profits, leaving the couple scrambling to pay their workers. 

Seaba and Tshikangavhadzi had gone into farming with romantic notions of how it might go. Both in their early 30s, they’d grown up in Soweto, a Black township south of Johannesburg that was synonymous with urban grit. “To me, cucumbers came from the grocery store,” Seaba says. 

But Tshikangavhadzi’s family had a background in farming, and in 2014, he, his mother, and Seaba began farming a plot of land leased from the Department of Agriculture. The farm was part of a government effort to redistribute land from white farmers—who, according to experts at Stellenbosch University, still own nearly 80% of the country’s farmable land—to Black ones. 

The leasing program got the family a good deal on the land itself. But there was another chasm they still had to cross to have any chance of keeping up with their white neighbors who had been running commercial farms for generations. That was the gap in knowledge. 

Seaba and Tshikangavhadzi knew they needed to learn everything they could about vegetable farming, as fast as they possibly could, and so they threw themselves into applying for mentorships, grants, and awards. 

But both say one of their most profound learning experiences came from their two engineered water measurement devices, which they received from VIA. 

Those two products are the fruits of Stirzaker’s career-long obsession with the small-farmer water problem. 

His first invention is what he calls a Wetting Front Detector (WFD). The funnel-shaped gadget is inserted into the ground to measure how deep moisture from irrigation and rain goes. For instance, it tells farmers if the water has reached a plant’s roots. The device also takes samples of the soil water that can be tested to measure salt and nitrate levels—key indicators of healthy soil. 

The other device, the aforementioned Chameleon, measures water suction, or how hard it is for the plant roots to extract water from the soil at any given time. Stirzaker says that what sets these two devices apart from other water management tools on the market is their price point (cheap) and how easy they are to use (very). 

The Chameleon, for instance, employs a simple color code to help farmers interpret its data. A reader lights up red if the soil is dry, green if it is moist, and blue if it is wet. 

Of course, Stirzaker is quick to point out, the colors alone don’t determine what a farmer does next. They are just a data point. “This is not a tech fix, it’s a people fix,” Stirzaker says. “People possess so much creativity to solve problems if they just have the right information.” 

The Power of Data 

On a recent morning, in a small room in a low-slung industrial park in Pretoria, a blocky metal machine gobbled plastic pellets. It whirred and beeped, and several seconds later produced a small plastic cylinder destined for the interior of a Chameleon sensor. 

When Stirzaker founded VIA in 2016, he was building nearly all his devices himself in his lab in Australia, then hauled suitcase-loads of them to the African countries where he worked. 

But since then, Stirzaker and his team, led by engineers Luan Steyn and Divan de Vaal, have devoted themselves to figuring out how to make nearly every piece of their technology, from the wiring down to the water sensing tip, locally in Africa. 

The idea, he says, is that the communities using the sensors should “not just be at the end of our value chain, but also at the beginning.” 

Today, nearly every part of the Chameleon—save its microprocessors and a few associated pieces—is made in South Africa, as is the WFD. And VIA recently opened a second production line for Chameleons in Blantyre, Malawi. 

To date, VIA has produced and sold nearly 100,000 WFDs and Chameleons in 20 countries, largely through projects and NGOs, who distribute them to small-scale farmers. But the organization wants to reach more farmers, and faster, and for that, Stirzaker says, they simply need to get bigger. 

That will help them reach even more farmers like Seaba and Tshikangavhadzi. 

Last year, the couple’s farm hit a major milestone. They obtained an inter- national quality and sustainability certification called the Global G.A.P. Among other things, this required that they show auditors how they were responsibly managing the farm’s water use. 

Easy. They just whipped out their Chameleon sensors and the case was closed. When the farm received its certification, they popped a bottle of champagne in celebration. 

Stirzaker’s device had made it easy to quantify the progress they’d made on the farm. But they already knew they were succeeding. 

Learn more about Virtual Irrigation Academy.

Author: Ryan Lenora Brown
Photographer: Lauren Mulligan