Terraced fields store more organic carbon than sloped ones — with implications for sustainable arable farming in hilly areas.
A team of researchers from China turned their attention to the soils of the Loess Plateau, renowned as the cradle of Chinese Civilisation. More recently, the area has been ecologically restored, with terraced agriculture a prominent landscape feature.
Comparing terraced and sloped fields
The scientists collected soil samples from 84 sites (77 terraced and 7 sloped) at 10 depth intervals, up to a depth of one metre. They dried and sieved the samples, then analysed soil organic carbon (SOC) by oxidising it using potassium dichromate in acidic conditions, a standard testing approach. They explored soil texture using laser diffraction, which determines the size of different particles by looking at how they scatter laser light.
The sites picked for the work represented different cropping types, while they also included five abandoned apple tree terraces. On the latter, the researchers then tested three different vegetation restoration approaches.
Topsoil drives carbon gains
From their analysis, they found that terraced wheat fields had 1.5 times more SOC in their first metre of soil than sloped, with the topsoil (first 30cm) showing particularly marked differences. Writing in the journal Scientific Reports, the scientists suggested that “converting some sloping land into terraces would enhance the carbon sequestration capacity.”
Impact of land abandonment on soil carbon
Terracing has long been associated with reductions in soil erosion, fertility retention and increased productivity. While the scientists’ results point to the addition of improved soil carbon performance to this list of advantages, they noted that such gains can be lost if land is abandoned — something that has seen an increase in the study area, as well as being a broader global issue.
While the SOC they saw in the abandoned apple tree terraces was lower than in those still in use, it fell short of statistical significance. The team also pointed to options to avert the loss of carbon storage, with planting tree species on terraces shown to result in higher SOC content than planting forage (alfalfa). In the study, Chinese red pine brought the highest SOC, and alfalfa was lower than natural grassland.
From these findings, they noted that “it is necessary to protect the natural grassland left behind [after land abandonment] and choose tree species with better ecological benefits when planting trees.”
Global relevance of terraced agriculture
Around 5% of the world’s arable fields (over 850,000 km2) are terraced, but the study suggests that there would be positive reasons to use the approach more in upland areas. While the findings have global relevance, the researchers point to a specific significance in China, bringing a farming approach practiced for millennia to bear on modern problems.
“In the face of China’s huge food pressure and the goal of increasing carbon sinks to mitigate global climate change, terraces have significance and importance,” they added. “Continuous strengthening of terraces management will give full play to their carbon sequestration role.”
Key takeaways
- Terraced fields stored 1.5 times more soil organic carbon than sloped land.
- Differences were most pronounced in the top 30cm of soil.
- Study adds carbon storage to known benefits of terracing like erosion control.
- Abandonment risks reducing soil carbon gains over time.
- Tree planting, especially Chinese red pine, boosted carbon on abandoned land more than forage crops.
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