Charred lands: fertile grounds for sustainable agriculture in Kalimantan?

Forest fire in Indonesia, 2007.

BOGOR, Indonesia (06 July, 2012)_ In the Amazon, it’s called Terra Preta. In the tribal tongues of Indonesia’s East Kalimantan province, it’s called tiem by the lowland Merap and punyuh by the upland Punan. In all three languages, the meaning is the same:“Black Soil,” an apt description of the dark, nutrient-rich soil pockets prized by forest-dwelling tribes in the tropics.

A multidisciplinary research team led by a pair of CIFOR scientists has found evidence that the “Black Soil” of Indonesia’s Kalimantan province, like its Amazon analogue, is “anthropogenic” – a product of decades, if not centuries, of human cultivation. They make their case in a new paper in the journal Forestry.

If borne out by further study, the sites in Kalimantan would be the first scientifically documented instance of Anthropogenic Dark Earths (ADEs) in tropical Asia. The phenomenon has been noted in Latin America from the early twentieth century. However, nearly 20,000 kilometres apart, both the Amazonian and Indonesian ADEs are thought to originate in the same style of farming: “Slash-and-char” cultivation rather than the more common slash-and-burn pattern.

“What we are seeing in [our research site at] Malinau [East Kalimantan] is evidence that ADEs caused by ‘Slash and char’ techniques leads to improved soil quality, and are not necessarily, as some believe, the result of some long-lost knowledge in the Amazon,” says Douglas Sheil, the lead author of the  paper and a scientist with CIFOR’s Forests and Environment Programme. “These improvements in the soil can sequester large-amounts carbon, protect forest diversity and help improve sustainable agriculture in regions that are already deforested and giving poor yields.”

“These soils could be developed in low-tech and low cost ways that can reduce pressure on land and improve sustainable food security where land is scarce,” he added.

Sheil cautions that it is not fully understood how ADEs originated. However, the 15-percent carbon levels exhibited in the soil are understood to be largely thanks to “char.”

Shifting agriculture—which includes both “slash and burn” and “slash and char” methods–is practiced by many tribal peoples.

With the “slash and burn” method, trees and other woody plant are cleared and burned when preparing land for planting — this generates soil nutrients that temporarily improve productivity. When the burn-off is thorough, leaving only ash, the soil enrichment is relatively short-lived and the field must lie fallow for longer before it is ready to re-use.

However, a partial burn-off, or “slash-and-char” method, enhances soil structure and provides a longer-lasting store for nutrients that are gained from various sources but likely reflect food processing and wastes associated with sustained human presence. Overtime, if the clearing-char-nutrient additions cycle is repeated, the result is a build-up of ADEs.

The increase in soil fertility allows indigenous populations to sustain themselves without the use of costly chemical fertilisers. It also helps to conserve forest diversity and boosts carbon sequestration five- to seven-fold, which can last for centuries, even millennia, compared to surrounding rainforest land.

From field interviews, researchers learned that farmers living in Kalimantan’s upper Malinau river basin, clear fields by a method more akin to “slash and burn.” “Slash and char” methods mainly occurred unintentionally, when frequent rain blots out the burn prematurely.

This was probably why only two plots of the 202 plots surveyed had the 15-percent carbon levels seen in the Amazon Terra Preta samples, said Sheil’s co-author and fellow CIFOR researcher, Imam Basuki.

Basuki adds that the new research presents a convincing argument for why slash and char methods should be used by local communities to improve the soil fertility. “This is solid evidence showing farmers and local policy makers that this system will increase their own rice productivity,” he added.

Although remote, the Malinau region is crucially important as a watershed for East Kalimantan, including the provincial capital. It is also a biodiversity “hotspot”, as recognised by the World Wildlife Fund in its “Heart of Borneo” conservation campaign.

All the more reason, Basuki said, to promote slash-and-char in Kalimantan. If soil enrichment through “slash and char” can be achieved inadvertently, how much more could be achieved through deliberate efforts?