DR SUSAN ORGILL, CHIEF SCIENTIST
Picture our soil as a bucket that holds carbon, and every season, we’re either topping it up (and hopefully, holding a bit more) or watching it leak. For a long time, Australian agriculture was carrying buckets with holes in the bottom. Centuries of cultivation, erosion, and overgrazing stripped away the organic matter (of which ~58% is carbon) that once acted like a sponge – holding water, feeding crops and microbes, and storing carbon.
But here’s the exciting part: we can patch the holes and start filling our bucket again. The question is: how much can we store, and how fast?
The frustrating – but exciting – answer? It depends.
Not all buckets are created equal. Soil type and climate set the bucket’s capacity: heavy clays hold more carbon than sandy soils, while sunlight, rainfall, and temperature govern how quickly photosynthesis drives carbon underground.
Other factors matter, too:
- Starting soil carbon concentration: Degraded soils are often close to ‘empty, presenting potential for strong gains. Rich, dark coloured soils might already be close to full.
- Magnitude of management change: Small tweaks bring incremental benefits, but transformative changes, like adopting multi-species pastures or integrating organic amendments, can dramatically enhance carbon accumulation.
- Depth of carbon storage: Carbon can be stored at the surface and deeper in the profile. The ‘bucket’ is typically less full deeper in the soil profile. Building carbon at depth improves soil stability and resilience, but typically takes longer to accumulate.
- Photosynthetic potential: It’s not just the plants you see above ground. Roots and their exudates feed diverse underground communities of microbes and fungi, transforming organic matter into stable soil carbon.
As for speed, research in Central NSW suggests we can add around 0.4 to 0.7 t C/ha/year. So, not quite a flood of carbon, but a steady drip-feed. And each tonne matters, improving water holding capacity, infiltration, nutrient cycling, and resilience to drought.
What’s the best way to fill our soil carbon bucket?
The first step is knowing our soil: its colour, texture, structure, pH, and constraints like nutrient deficiency, salinity, or compaction. Every management decision is like turning the tap on or off. But here’s the catch: the best results don’t come from blasting carbon into the soil bucket like a garden hose on ‘jet’ mode. Sudden, heavy inputs or poorly managed practices risk splashing gains away. The trick is steady, well-distributed inflows – the ‘shower’ mode.
And if we follow the hose analogy, multi-species pastures are the gold-plated hose reel. I recently saw this in action on a farm near Yass, NSW: tillage radish creating biopores, inoculated legumes fixing nitrogen, and oats pumping root exudates deep into the soil. The farmer is now preparing to sow a perennial pasture – a carefully matched mix of deep-rooted grasses, legumes, and forage herbs suited to the soil and position in the landscape. All of it is driven by engaged, skilled management, and a clear commitment to building carbon-rich, resilient soils.
Other proven practices we can use to build soil carbon (and keep it there) include:
- Balanced nutrient strategies (C:N:P:S) so stubble decomposes efficiently and feeds soil biology.
- Pasture phases and cover crops to introduce diversity that keeps roots channelling carbon into the soil year-round.
- Controlled grazing at high-intensity and short-duration, followed by long rest periods to boost regrowth and root depth (e.g. one-day grazing followed by 40-60 days’ rest on the New England Tablelands, depending on enterprise size and paddock numbers.)
Fill your bucket, and set your farm up for a productive, resilient future
Healthy soils are the foundation of profitable, productive farms. They hold water, cycle nutrients efficiently, and give flexibility in how, when, and what you produce. They’re also a powerful ally in tackling climate change, locking atmospheric carbon where it belongs: in the ground.
The question isn’t whether we can fill our bucket. It’s whether we’re ready to commit to the mix of science, patience, and management required to keep it topped up.
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