While no-tilled crops are widely considered to be among the best ways to sequester carbon, the actual amounts may actually be tied to soil type, soil drainage and soil depth.
It’s well documented that no-till effectively stores carbon within 10 inches of the soil surface, says Humbeto Blanco. But little is known about carbon storage in deeper soil profiles, adds the Ohio State University research scientist.
He maintains most carbon-sequestration studies have focused on what’s available in the layer of soil near the surface rather than the entire soil profile. A lack of data from the entire soil organic-matter profile means the effects of no-till on carbon sequestration and offsetting carbon dioxide emissions aren’t totally conclusive.
Go Deeper With Research
As a result, Blanco and soil scientist Rattan Lal decided to evaluate the amount of carbon stored to a depth of 25 inches in both no-tilled and tilled fields.
Data collected from 11 soils in Kentucky, Ohio and Pennsylvania demonstrated that concentrations of carbon in subsoil layers of no-till fields were low. In some cases, the amount of carbon stored in subsoil layers in tilled fields was actually higher.
Blanco says the research indicates that no-till increases soil organic matter in the upper layers of some soils, but doesn’t always store more carbon throughout the entire soil profile than with tilled soils. This suggests no-till’s impact on carbon sequestration may depend on soil type, sampling depth, drainage and several other factors.
While the total soil organic carbon found to a depth of 25 inches with no-till was similar to those found with tilled soils, there were a few instances where the total carbon pool was 30% higher in tilled soils.
The researchers theorize that the reason more carbon was found in deeper soil profiles in tilled fields was because the plowing process mixes residue at lower depths. In some instances, plowing may loosen compacted soil enough to allow plant roots to extend deeper in the soil.
The disparity may be related to differences in soil profile characteristics and the ability of roots to grow deeper in tilled soils. But the main fallacy of these conclusions is that fewer acres are being plowed each year, and this certainly wouldn’t likely be a popular option.
Stable Vs. Unstable Carbon
The researchers also raised the question as to whether carbon stored near the surface is stable since most carbon dioxide is released from near the soil surface. As a result, they say it’s essential to avoid making generalized comments about no-till and sequestered carbon.
The amount of carbon that can be sequestered from the soil must also be evaluated in terms of no-till’s numerous benefits, including reduced fuel, labor and equipment needs, less erosion, improved soil productivity, increased wildlife habitat, better methods of maintaining and conserving soil water and higher net profits for growers.