Capturing Carbon in the Cane

We stood and watched the air in front of us become thick with smoke, the odd human figure appearing and disappearing within it like mist wraiths as they moved up and down the lane between the cane fields. ‘Do you think we should get in there and help?’, one of the workers I was standing with asked. ‘Nah. I think they’ve got it covered’, the other replied.

The owner of the cane farm, Robert, had made the difficult decision to burn the field despite the strong winds, as the harvester was on its way here to get their quota of sugarcane, and they needed to have the fields ready for it. So it was all hands on deck, and the three of us were each carrying a beater (a stick with a rubber flap at the end to put out fires) and supposed to be on the lookout for ‘floaters’ (flaming pieces of sugarcane that drift with the wind into neighbouring fields). I wasn’t looking forward to having to go charging into the fields to find any resulting spot fires.

It had started quietly, with Robert walking along the downwind edge of the field, stroking his flaming torch against the undergrowth. The fire ate its way slowly against the wind, the air filling with smoke and the sound of popping and crackling. After some time they set fire to the upwind side of the field and it quickly became a conflagration, accompanied by a roar like hundreds of exploding firecrackers.

The thick smoke pouring into the sky seemed to go against the reason I’d come here. But I was seeing a practice normal amongst many cane farmers: using fire to burn the undergrowth while leaving the sugar cane intact, allowing easier access for the harvester.

‘This is the least sustainable thing I do’, Robert had told me. Despite the burning, he has somehow managed to almost quadruple the levels of carbon in his soil. ‘If all the cane farmers in Australia did what I’m doing,’ he’d told me over the phone before I came, ‘then it would remove about seven years of Australia’s carbon emissions from the atmosphere’. I was intrigued and keen to see for myself how he did it, but it was to be a puzzle that I needed to put together piece by piece.

It turns out that Robert hadn’t set out to increase his soil carbon. He’d been trying to tackle an altogether different conundrum.

Earlier that afternoon, having just cycled up through the Northern Rivers in northern NSW, I came over a rise on my bicycle and a gap in the trees revealed a vista looking out over Robert’s cane fields. A mozaic of different shades of green, yellow and brown, crisscrossed with drainage canals and dirt access roads, and the odd truck kicking up dust as it drove through the middle of it all.

Following the instructions I’d been given I turned off the main road and followed a wide canal in to the fields, eventually coming around a bend to find a marquee set up next to a fallow field. Two staff from Southern Cross University were setting up a table with all sorts of soil testing equipment. They were happy for me to join them in the shade of the marquee, and chatted while they waited for their students to arrive.

It seems that Robert’s farm made an excellent case study for what they were teaching. This whole area was once a she-oak swamp, which was cleared and drained long ago and used for cattle and sheep grazing. The land has been in Robert’s family for generations, and he would later tell me how periodic flooding from the nearby Tweed River would sometimes be bad enough to drown all the livestock. They noticed that the small amount of sugarcane they had would survive, so in the 1960’s they decided to switch entirely to growing sugar. But they didn’t realise there was something in the soil that would almost spell their ruin.

As they continued to farm the land, putting in more drainage, their soils became increasingly acidic, damaging their crops.

The demonstrator from Southern Cross University explained ‘acid sulfate soils’ to me. Common in many parts of the world, these are waterlogged soils containing naturally occurring bacteria that lay down sediments of iron sulfide. This is harmless if it’s not disturbed, but if it’s dug up or drained it comes into contact with the air and oxidises to form sulfuric acid, which wreaks havoc, damaging crops, buildings and other infrastructure.

I’m shown aerial ‘before’ photos of Robert’s farm, large tracts of land streaked with yellows and reds: signs that sulfuric acid was infecting his land as it reacted with other minerals to form these bright colours. Robert was faced with a choice between taking extreme measures or going under.

A large bus soon arrived and parked next to the marquee, and a crowd of ‘students’ filed out and gathered around the display. They looked older than I’d expected, and apparently there were local councillors and policy-makers amongst them. The university staff began their demonstration, showing how a soil sample is taken. They inserted a cylindrical metal shaft, like a giant narrow apple corer, deep into the mud, twisting it and pulling out the long rod of soil that had entered its hollow core. They demonstrated testing small samples of this from different depths, and the test tubes containing the most acidic samples soon started bubbling and frothing.

Our host Robert soon arrived in his ute, apologising for being late — he’d been away dealing with the harvester. This was the first time I’d seen him: an older man of average height wearing a flat cap over his short grey hair.

Robert explained to the group how he had worked alongside experts from the university to try to turn his acid sulfate soils problem around. They tried many tactics, including applying lime, and laser-levelling the land to prevent overdraining. They also reduced how much they cultivated or tilled the fields, to expose less of the soil to the air.

Acid sulfate soils can’t be removed, so they were hoping to merely stabilise them. They started getting results back from the university’s soil testing showing the oxidation had not only stopped, but the acidity was decreasing! They also found the soil carbon content had increased, and this seemed to be buffering against the acidity.

So began Robert’s journey with soil carbon.

The presentation wrapped up, and Robert left the participants milling around and came over to meet me, inviting me to follow him. He hopped into his ute and drove off down a dirt track through the cane fields, with me trailing behind on my bicycle. We pulled up at an intersection where his team of workers were waiting to start burning the cane fields. I was introduced and then we got to work — well, I was more of a spectator.

Burning the fields releases all that carbon into the atmosphere. Robert explained that he only burns about 10% of his crop. Just his ‘two year old’ cane that has been left to keep growing for a second year before harvesting, and where the undergrowth has become especially dense.

As dusk fell and the light began to fade, I eventually handed over my beater and rode my bike up to the shed on the hill to set up camp. Robert and his team continued burning the fields until after dark. From the hillside where I was camped, the burning cane and tower of smoke made a dramatic sight. Soon the harvester arrived and started harvesting the freshly burnt cane, its lights clearly visible in the night.

Robert came to pick me up the next morning, driving me down into the cane fields to join them as they burned more fields. The harvester had started up again that morning. It came to them five times over the harvesting period, and they needed to make sure that enough fields were ready for it.

As we drove between the fields, he told me his soil carbon content has increased from 2 to 3% to about 8%. There’s currently about 200 tonnes of carbon in his soil per hectare, totalling 20,000 tonnes across his 100 hectares. He says the carbon enriched soil has also benefited his cane growing.

He explained how they used to plant and harvest each field then get three ‘returns’; that is, three subsequent years of harvesting where each time the cane regrows from the original stalks. They’d then need to leave it fallow for a year, planting a legume crop of soy beans, faba beans and rye grass to fix nitrogen and improve the soil. Now they’re able to plant and get four returns before a fallow year, simply because the soil is healthier.

Every 1% increase in carbon allows his land to absorb an extra 120,000 litres of water, reducing run-off and improving drainage. In the floods of 2017, his fields were under three metres of water with no cane showing. It resulted in the highest value harvest in his lifetime. He says it’s because his carbon-enriched soil acted like a sponge, holding on to the water for longer.

He’s also been able to cut his fertiliser use by 30%-40%, with analysis showing that more fertiliser wouldn’t bring any extra benefit. It’s saving him a lot of money, and the crops are still getting better.

But how did he do it? I still didn’t have a clear picture.

Later that morning, Pip, the presenter from the TV show ‘Landline’, arrived with her team to interview Robert for a piece they’re doing on soil carbon, and I sat back and watched the experts in action. I then joined them in their car as they drove to different parts of the farm to get the shots they needed. Pip helped to fill in some more of the picture for me.

‘Have you heard of the ‘no till’ or ‘minimum till’ movement?’, she asked. In the 1980s and 90s a movement grew amongst Australian farmers to do away with the plow. Plowing rips up and turns over the soil, and was mainly used to reduce weeds, with farmers sometimes plowing two or three times to turn the weeds under. But it also exposes and dries out the soil. With the development of better herbicides like glyphosphate it allowed farmers to plow or till their soil less.

By not disturbing the soil as much, it also improves soil carbon. ‘You know that smell of freshly plowed earth that so many farmers love?’, Pip asked me. ‘That’s the smell of the soil carbon oxidising.’

Robert brought down his tractor so that he could show us the large contraption attached to the back of it: a ‘bed renovator’. He demonstrated using it to prepare the fields for planting, driving it up and down the furrows, and explained that it disturbs the soil 80% less than conventional methods.

He pointed out some of the bare fields, specifically the long mounds and furrows that are strewn with ‘trash’: debris such as bits of cane stubble, stalks and leaves from previous crops. He’s learnt to leave this trash on the fields, as it provides extra carbon for the soil. The extra ground cover also helps to retain moisture and stop the soil heating up as much, which is important as the climate gets hotter.

Most farmers don’t like doing this, he told me, as it looks messy with all the trash left on the fields. They like the traditional look with nice clean brown fields. There are also practical challenges to this new way of farming. Robert has had to invest in new equipment and learn how to seed directly into the stubble.

So, he does minimal tillage, leaves the trash on the fields, what else? ‘Fungi’, Robert tells me.

Robert tried to explain the role that fungi plays. At first they were finding the cane trash wasn’t breaking down into the soil. He received advice from the Head of the Department of Agriculture in New Zealand to try spraying a minute amount of nitrogen on the residue — it worked. The improved carbon and nitrogen ratio encouraged the growth of certain fungi called endophytes, which help to break the trash down into the soil and increase the carbon content.

Wanting to better understand the role of fungi, I later phoned Guy Webb from the non-profit organisation Soil C-Quest. Their goal is to fast track the research, development and deployment of biotechnology to sequester carbon.

He told me that Robert is encouraging the growth of a range of different fungi. But what if we could inoculate our crops with specific species of fungi that maximise the sequestration of carbon into the soil?

They’ve found that certain fungi strains called ‘melanised endophytes’ work in a symbiotic partnership with the plants to produce melanin, a carbon compound that is much more resilient to breaking down and being released back into the atmosphere. Testing has shown dramatic increases in soil carbon in only a matter of weeks.

It’s become standard to inoculate legume crops with rhizobium bacteria to improve nitrogen fixing. Guy and his team want to deploy an inoculum of these melanised endophytes in the same manner, to help sequester carbon. ‘It would be like a probiotic’, Guy says, ‘a microbe that lives with the plant and delivers benefits both to the plant and the climate.’

Guy sees soil as the biggest terrestrial carbon sink available. Farm trials are still in early stages, but he believes that rolling out a carbon inoculum for farmers worldwide could offer a huge opportunity for climate change mitigation.

Back at the cane farm, Robert’s soil carbon levels are almost at saturation according to the soil experts, but Robert still wants to push for higher.

He says that thanks to his higher soil carbon levels, his drainage is better, he needs less inputs like fertiliser, the work required is less, and his bank balance is as good as it’s ever been.

‘Why aren’t more farmers doing it then?’, I ask. ‘They don’t understand it’, he replies, ‘and they won’t until we can research the science and publish papers.’ They tried publishing a scientific paper in the early days about the increased soil carbon content, but it got rejected — levels of soil carbon that high hadn’t been seen before, so they weren’t believed.

Doing scientific research to validate his methods is expensive and takes time. But then in 2014 he received a prize for carbon sequestering and won $10,000 worth of soil testing. Since then 12 PhDs have been done on Robert’s farm. The science is now coming along rapidly.

With the final pieces of the carbon puzzle having fallen into place in my head, I say farewell to Robert and set off from his farm on my bike. It’s been fascinating to see what can be achieved when farmers and scientists work together. I’ll be passing many more cane farms as I journey north, and I’m filled with renewed hope as I think of the potential they now offer.

Huge thanks to Robert and his team for hosting me on his farm, and to the crews from Southern Cross University and Landline for taking the time to talk with me.

Thanks for following my journey! Can you donate to help keep me pedalling forwards?