North Coast croppers have long sought a cost-effective way to improve organic carbon content in their soil and boost yield, but a group meeting at Clovass via Casino on Tuesday were told the only ‘silver bullet’ was time.
Retired soil scientist Dr Bob Aitken, Yamba, advised the Coastal Grower Solutions Workshop ‘how to manage heavy clay soils’ that adding organic matter improved crop yield and promoted resilience through biology, but growing carbon content was a long and slow process.
“The best peat soils on the Tweed have 20-30 per cent organic matter,” Dr Aitken said. “Medium levels for cultivated soils are around 3.5 per cent. For those of you thinking of increasing your carbon content to those high levels – you’re not going to gt there.”
And yet growers realise a do-nothing approach is not the answer. Alan Munro, Woodford Island, realised the need to add organic matter and built a two-row augur that delivered a band of compost and sugar mill ‘mud’ in half-metre wide strips. Scientific studies showed a boost in sugar can yield statistically nearly the same as adding urea at the rate of 230kg/ha. But the cost was too dear. Further studies are continuing with council green waste.
Of course most growers are willing to try soil amendments in order to reduce their reliance on chemical inputs so they and their children can farm into the future. And when land on the coast has a higher value why not invest back in?
Soil development officer at Wollongbar, Abigail Jenkins, said the best way to increase organic matter was to grow healthy and varied plants, with a diverse range of root architecture. When it came time to working soil there needed to be a balance between too much stimulation with resulting loss of carbon, and not enough.
North Coast slay soils are naturally high in magnesium and prone to compaction when wet, but they do dry out to the point of cracking which allows air, water and nutrients to get to new depths and condition that soil.
“Use that cracking to your advantage,” she advised.
Meanwhile, Mid North Coast agronomist Matt Thompson, Taree, suggested lime over gypsum at high rates to boost yield and improve soil quality but stressed the importance of creating soil where calcium is twice the presence of magnesium, not the other way around.
“Apply gypsum only when the calcium percentage is above 60 per cent,” he said.
Time heals all
North Coast country varies from clay that cracks when dry to light, freely draining sandy loam but wherever producers farm they are now are increasingly keen on investing back into their greatest asset.
“You can’t fix soil simply by putting on more NPKS,” said Matt Thompson, Mid Coast Agronomy, who advises lime over gypsum in conjunction with reduced till to bring a cropping paddock back into balance. And yet he says the liming affect will be lost if it is not topped up.
Soil Development Officer Abigail Jenkins, Wollongbar, said the aim of croppers should be increasing humus. But to make a lot of carbon you need a lot of nitrogen, phosphorous and sulfur. “The best way to grow carbon is to grow organic matter over time,” she said.
