We hear a lot about trees, and even seaweed, as carbon sinks to reduce the amount of harmful carbon entering the atmosphere, but not so much about the relationship between soil and the climate.
Retired Australian CSIRO climatologist and soil microbiologist Walter Jehne is touring the country talking to farming groups about an idea called the soil 'carbon sponge' - designed to cool the planet by rehydrating soils. They make for more resilient and productive farms too.
Photo: RNZ / Alexander Robertson
Jehne told Jesse Mulligan that over the last 200 years we have been “collapsing” the soil.
“We’ve been systemically collapsing the soil’s structure, effectively concreting catchments, so how do we rebuild healthy structured soils so they can infiltrate and retain water in the in soil reservoirs and then make that available?”
The soil’s ability to store moisture is a key part of the whole “terrestrial eco-system,” Jehne says.
“Its structural health and the capacity of that soil to make nutrients available but also to retain and make available water.”
The traditional approach of chasing yield has led to ever more inputs, he says.
“We’ve just been adding more and more inputs with the intention of pushing yields – cultivation, excessive fertilisers, irrigation, bare fallows to exclude weeds – and basically all of those processes are really burning carbon out of the soil, oxidising carbon out of the soil.”
He calls it the “more on” mentality.
He says the first step for farmers is to reduce harm to the soil.
“When we cultivate excessively we obviously release carbon, so the question is how much do you need to cultivate or can you use plants, cover crops with deep, strong tap roots that can actually open that soil and we don’t need to cultivate?”
Once the soil is healthy then fertiliser use can come right down, he says.
“If we’re using excessive nitrogen, every gram of nitrate burns off 30 grams of carbon microbially, so how do we improve the bio-fertility of soils? Simply by increasing the availability of those nutrients in the soil rather than having to rely on adding them."
Likewise, biocides attack beneficial fungi, he says.
“We’re adding enormous quantities of biocides to kill insects, fungi, weeds and yet nature can beat all of these things just by growing healthy plants, out-competing the diseases and basically avoiding the need for these toxic biocides which kill the fungi which drive the productivity of those soils.”
Jehne says the idea of regenerative agriculture is catching on.
“It’s really bottom-line stuff, return on investment, because the input costs in conventional agriculture, the thing that’s killing people now with markets less certain, these lower input, more productive resilient agricultural systems will get to that tipping point and we’re part of creating that wave.
“Scientists and policy people everywhere get it. We’ve got to build natural capital and resilience because in Australia now people are getting crops two years out of five, whereas they used to get four years out of five – two years out of five is just financial disaster.”
Photo: supplied
Walter Jehne is speaking at the Lakeside Soldiers Memorial Hall, Harts Road, Leeston
Wednesday 11 March 10.00am - 12.00 noon; Otago University Dunedin, Thursday 12 March 5.30pm - 7.30pm and the Town and Country Club, Gore Monday 16 March 9.15am-11.30am.
