Old Sorghum, New Roots: What ‘Lazy’ Modern Crops Mean For Africa’s Soils
On a dry August morning outside Gokwe, Midlands Province, 62-year-old farmer Mai Ncube kneels in her field, turning up clods of soil with a hand hoe. Side by side, two crops tell a quiet story. The tall hybrid maize she bought on credit stands lush but shallow-rooted near the fertiliser bands. A strip of red-brown sorghum, saved from her grandmother’s seed, looks leaner above ground – yet when she tugs at a plant, its roots run deep and wide.
She doesn’t have a word for “root exudates” or “circular nutrient economy”. What she does know is this: when fertiliser is short, the old sorghum still feeds the family.
New research from the University of Queensland (UQ) in Australia suggests farmers like Mai Ncube may be holding a key to future food security – not in the grain we see, but in the hidden chemistry of roots underground. The study, published in npj Sustainable Agriculture, compared modern sorghum varieties with traditional “landrace” sorghums and found that old varieties are far better at pulling phosphorus from hard-to-access and recycled sources.
This matters for every village in Zimbabwe, and for African agriculture at large, because the world’s supply of mined phosphorus – the backbone of modern fertiliser – is finite, concentrated in a few countries, and increasingly expensive.
What Did The Sorghum Study Actually Find?
The UQ team, working in the School of Agriculture and Food Sustainability, grew modern sorghum from a breeding programme alongside traditional or landrace sorghums under controlled laboratory conditions. They then fed the plants either conventional, soluble phosphorus fertiliser or less soluble, recycled phosphorus sources.
Project lead Dr. Michael Walsh said the differences were clear.
“Growing the sorghum plants in laboratory conditions revealed some stark differences,” said Dr. Walsh, a researcher at the University of Queensland. “The traditional sorghum outperformed the plants from a modern breeding program when they were given less soluble and recycled phosphorus — they took up more of this vital nutrient and grew bigger.”
The scientists analysed more than 20,000 chemicals released by the roots – known as root exudates – to find out what was happening in the soil around each plant.
“We analysed over 20,000 root-generated chemicals to identify exudates that acted like pickaxes, unlocking phosphorus so that the crop could grow,” Dr. Walsh said.
Modern high-yield sorghum, bred for decades in the presence of cheap, soluble fertilisers, did well when phosphorus was easily available. But as soon as the team switched to less soluble, recycled forms of phosphorus, the modern varieties stumbled. Traditional landraces, shaped over generations in low-input farming systems, kept growing strongly.
“Years of breeding crops in the presence of easily accessible fertilizers has created high-yielding crops for modern farms, but they can be ‘lazy’ underground,” Dr. Walsh said. “As soon as the phosphorus was less soluble and harder to access in our experiments, the modern sorghum was outgrown by the traditional sorghums which had adapted to grow in environments with less available nutrients.”
FFA Explainer:
Root exudates are tiny organic compounds that plant roots release into the soil. They can attract helpful microbes, dissolve locked-up nutrients like phosphorus, and even fend off some diseases. Different crop varieties release different exudates – and that can decide who thrives when fertiliser is scarce.
Why Is Phosphorus A Big Deal For African Farmers?
Phosphorus is one of the three main nutrients in most fertiliser bags, alongside nitrogen and potassium. In Zimbabwe, as across much of Africa, it’s what helps maize, sorghum, wheat, and soya set strong roots and full grain.
Most phosphorus fertiliser comes from phosphate rock, mined and processed into products like single or triple superphosphate. Honorary Professor Susanne Schmidt, who worked on the UQ study, warns that this system is under pressure.
“Mined and refined phosphorus is a non-renewable resource, and it is subject to price volatility and supply chain interruptions as only few nations possess deposits,” she said.
When international prices spike or foreign currency is tight, smallholders feel it first. Bags of Compound D or Compound L stay in the shop. Fields go hungry. Yields drop.
Yet while we import expensive fertiliser, we flush away vast amounts of phosphorus every day – in livestock manure, human waste, and food scraps.
“A circular nutrient economy will be the way to a sustainable food future,” Professor Schmidt said. “That means reclaiming agricultural inputs like phosphorus from wastes, including livestock manure and human effluent, and unavoidable food waste.”
For Zimbabwe, which has committed under NDS1 to raise agricultural productivity while protecting natural resources, this idea fits neatly with broader sustainability goals and the African Union’s Agenda 2063 vision of resilient, climate-smart food systems.
What Is A Circular Nutrient Economy, In Practice?
A circular nutrient economy sounds abstract, but on the ground it can be as simple – and as complex – as making sure nutrients don’t leave our food system for good.
- Instead of dumping raw sewage into rivers, we treat it and recover phosphorus for safe fertiliser products.
- Instead of letting manure wash away in storms, we collect and compost it or process it into pellets.
- Instead of burning or landfilling market and household food waste, we turn it into organic fertiliser.
Countries like Sweden and Germany are already experimenting with fertilisers derived from human waste and industrial by-products. Across southern Africa, there’s growing interest in turning manure, abattoir waste, and even ash into safe, regulated fertiliser products.
FFA Explainer:
A circular nutrient economy keeps nutrients like nitrogen and phosphorus cycling within agriculture for as long as possible. Instead of a one-way flow – mine, apply, lose – it focuses on recovery, recycling, and smart use. This reduces dependence on imports, protects water bodies from pollution, and cuts greenhouse gas emissions.
But there’s a catch. Many recycled fertiliser products release phosphorus more slowly or in less soluble forms than factory-made chemical fertilisers. If our crops have become “lazy” underground – relying on spoon-fed phosphorus – they may struggle to use these new sources efficiently.
This is where those old sorghum landraces come back into the picture.
How Do Traditional Sorghums Outperform Modern Varieties?
The UQ researchers didn’t just weigh plants and measure phosphorus in the leaves. They looked closely at what the roots were doing chemically.
Traditional sorghums released suites of root exudates that acted, in Dr. Walsh’s words, like “pickaxes” – helping dissolve or detach phosphorus bound to soil particles or trapped in recycled fertiliser granules. Over decades in low-input, often marginal environments, farmers had unconsciously selected for varieties that could fend for themselves in poor soils.
Modern sorghums, bred in research stations with consistent applications of highly soluble fertiliser, didn’t need those same underground skills. Above ground, they may yield more in high-input systems. Below ground, though, they can be less curious, less aggressive – slower to explore tough soil and unlock tight nutrients.
“This study has shown traditional sorghum was more efficient at drawing phosphorus from the soil, so these landraces are a great source of information,” Professor Schmidt said. “Breeding crops with a view of their root exudates could improve phosphorus use efficiency and ensure agriculture is ready for reclaimed nutrients.”
The research – formally titled “Non-targeted root exudome profiling reveals genotype-specific strategies for phosphorus use from conventional and recycled sources” – is, in the team’s words, proof-of-principle. Field trials with sorghum and other grains are planned next.
What Does This Mean For Zimbabwean Farmers Now?
Most smallholders don’t have the luxury of choosing between “conventional” and “recycled” phosphorus. They use what they have: a bit of basal fertiliser, some cattle kraal manure, compost pits, ash from the cooking fire, and whatever microdosing they can afford.
That reality makes the UQ findings especially relevant for Zimbabwe, where fertiliser prices have repeatedly spiked and where many communal and A1 farmers continue to plant traditional cereals such as sorghum and millet alongside maize.
In Gokwe, Mai Ncube describes how her family copes in years when fertiliser is scarce.
“Maize yeku shop inodya fertilizer yakawanda. Kana isipo, unongowana mashanga,” she said – the hybrid maize from the shop eats a lot of fertiliser; if it’s not there, you harvest mostly stalks. “Ndosaka tichichero zviyo zvedu zvekare. Zvinoshingirira nenzara yevhu.” – That’s why we still plant our old sorghum. It endures the soil’s hunger. [Illustrative — verify or replace]
Her observation lines up with the science. Traditional cereals – sorghums and millets – have long been known to perform relatively well in poorer soils with limited inputs. The UQ work gives a biochemical explanation for at least part of that resilience.
For farmers and extension officers, a few practical implications stand out:
- Don’t abandon landraces too quickly. While modern hybrids bring yield potential, farmer-saved sorghums and millets may hold genetic tools – especially in their roots – that future breeders will need.
- Value manure and organic matter. Even if phosphorus in manure is less soluble than in bag fertiliser, crops with the right root traits can still access it effectively.
- Mix crops and varieties. Intercropping or rotating modern and traditional cereals can spread risk between input-hungry and input-efficient crops.
For youth and women’s farming groups experimenting with climate-smart cereals, this could be an opportunity to position themselves at the frontier of “below-ground breeding” – using citizen science and on-farm trials to identify which traditional lines perform best under low-input, manure-based systems.
How Should Breeders And Policymakers Respond?
The UQ team is clear: yield still matters. Farmers and nations can’t afford to go backwards on productivity. Yet the study suggests that, as we adapt to a world of more recycled fertiliser and less easy phosphorus, breeding pipelines need to shift their gaze underground.
Traditionally, breeders have selected plants based on traits we can see – grain size, plant height, days to maturity, resistance to visible diseases. The new research calls for root traits and root exudates to join that list, especially for staple crops that will rely increasingly on recycled nutrients.
For Zimbabwe, that could mean:
- Encouraging the national breeding programmes to screen sorghum, millet, and maize collections not just for drought or disease tolerance, but also for phosphorus use efficiency and root exudate profiles. [SOURCE REQUIRED]
- Partnering with universities and international centres such as ICRISAT to explore African landrace sorghums in more detail.
- Aligning soil fertility policies with the move towards a circular nutrient economy under NDS1 and the SDGs, including safe recovery of phosphorus from urban and agro-industrial waste streams. [SOURCE REQUIRED]
There’s also a regulatory and research gap. If Zimbabwe and its neighbours are to use recycled fertilisers at scale – including products derived from sewage or industrial waste – they will need standards for safety and quality, along with agronomic trials to test performance on key crops.
This is where the UQ finding about “lazy” roots becomes a warning. If fertiliser policy moves in one direction – towards slower-release, recycled phosphorus – while breeding remains locked in another – favouring varieties that expect spoon-feeding – farmers could be caught in the middle with poor yields and rising risk.
Aligning breeding, soil fertility strategies, and circular economy policies is not just scientific tidiness; it’s insurance for future harvests.
What Questions Remain Unanswered?
The UQ study was a controlled experiment – a careful laboratory proof-of-principle. The team themselves say they are keen to test sorghums and other grains in the field, where temperatures swing, microbes swarm, and roots compete with weeds.
Important questions for African conditions include:
- How do these promising landrace traits perform across different soil types, from the Kalahari sands of Matabeleland to the heavy clays of Muzarabani?
- Can we identify low-cost field methods for screening root traits, so breeders aren’t confined to expensive labs?
- How do root exudates interact with local soil biology – the mycorrhizal fungi, bacteria, and termites that already work our fields?
- What happens when we apply mixed fertiliser strategies – a bit of Compound D at planting, manure in the basins, and recycled products from local waste treatment plants?
Answering these questions will take partnerships between international researchers, African universities, extension services, and farmers themselves. It will also require financing – from government, private sector, and climate funds – to support long-term soil health work instead of chasing only short-term yield gains.
Still, the direction of travel seems clear. As Professor Schmidt puts it, reclaimed nutrients are coming.
“Recycled nutrients will become very important in the future,” she said.
That future is closer than we think in African cities, where sewage treatment upgrades, organic waste recycling companies, and climate-smart urban planning are all on the agenda. The question is whether our crops will be ready to make full use of those recycled nutrients when they arrive.
Where Does This Leave Farmers Like Mai Ncube?
Back in Gokwe, the sun climbs higher as Mai Ncube finishes her inspection. She pulls a few sorghum heads, rubs the grain in her palms, and talks about the coming season: seed money, fertiliser rumours, the risk of another mid-season dry spell.
For now, her strategy is simple. She’ll plant the hybrid maize again – because when the rains are good and fertiliser is available, it fills the granary. But she’ll also keep a broad strip of her grandmother’s sorghum in the field, and another in the seed gourd hanging from the kitchen rafters.
Science is catching up with her wisdom. The UQ study reminds us that those old sorghum lines aren’t just cultural heritage; they’re living libraries of traits we may desperately need in a world of recycled fertilisers and tightening phosphorus supplies.
If breeders, policymakers, and farmers can work together to read that library – from the grain to the roots to the invisible “pickaxe” chemicals in the soil – Africa’s smallholders will be better placed to feed their families, their nations, and a warming, crowded planet.
As Mai Ncube dusts the soil from her hands, she looks over her field and smiles.
“Chikafu chedu chiri pasi pevhu futi,” she says – our food is also beneath the soil. [Illustrative — verify or replace]
The new science agrees.
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