19-year study shows we’ve been undervaluing how much compost can boost carbon capture

//19-year study shows we’ve been undervaluing how much compost can boost carbon capture

19-year study shows we’ve been undervaluing how much compost can boost carbon capture

It’s no secret that organic farmers believe in compost, but just what role compost plays in soil’s ability to store carbon – and keep it out of the atmosphere, where it contributes to climate change – has been less clear.

A recent study from the University of California suggests that compost plays a larger role than once thought in building soil carbon.

It also found that carbon levels fluctuate more in deeper soil than most evaluation methodologies tend to account for. In practical terms, the findings could mean compost has been undervalued by agricultural incentive programs, and that we’ve been measuring carbon levels in soil all wrong.

Nicole Tautges, co-author of the study, says it wasn’t a surprise to find that compost is good at helping soil store carbon – it’s where exactly it does this that was revealing.

“The surprising piece was that it raised soil carbon between one and two meters deep. Because the big question is, ‘How does the carbon get down there when we’re only applying it in the top foot?'” adds Tautges, the chief cropping systems scientist at the UC Davis Agricultural Sustainability Institute.

Her team has hypothesized that it has to do with how water moves through soil, and they plan to continue studying its movement. But just demonstrating the importance of soil depth could be significant, both for increasing the value that farmers and policymakers place on compost application and also, eventually, for how soil carbon measurements are taken.

“When you only measure the top foot, there’s potential to both over- and underestimate carbon storage in our agricultural soils,” says Tautges.

In the study, which was published this summer in the journal Global Change Biology and conducted at a long-term research site the university initiated in 1993, the researchers measured soil organic carbon at five different depths down to two meters over a period of 19 years.

They compared the carbon levels across a number of different cropping systems – conventional, conventional with cover crops, and one that included the application of compost alongside cover crops.

Researchers found that systems using cover crops alone not only failed to store more carbon, they actually lost significant amounts of carbon in the soil below about a foot deep. The system that used both cover crops and compost, however, had significantly increased soil carbon content over the length of the study – about 0.7 percent annually.

That may sound like a small number, but it’s enormous in the context of soil, where change is slow and gradual. The “4 per 1,000” initiative has called for a 0.4 percent increase in soil carbon annually around the globe as a way to combat climate change.

By |2020-10-21T08:21:02+00:00October 21st, 2020|Uncategorised|Comments Off on 19-year study shows we’ve been undervaluing how much compost can boost carbon capture