New relevance for an ancient farming trick

A millenniums-old fertilizing technique could help play a significant role in restoring nutrient-poor soils while combating global warming, according to a team of scientists from the University of Delaware.

For years, some archaeologists and sustainable-development activists have known of the technique, which uses ground charcoal. It was first uncovered as scientists studied a 1,500-year-old soil-charcoal deposit in the central Amazon. There the soil was enriched by charcoal from tree bark and animal bones. After analyzing it, the scientists found that it was some of the richest soil on the planet.

Typically, farmers in developing countries use compost, animal waste, and plant debris to enrich their land. But these decompose quickly, releasing carbon dioxide into the atmosphere over short time periods. Once it's applied, charcoal, or "biochar," would lock its carbon in the soil for hundreds of years. Moreover, the charcoal has a high nutrient level; it can capture and slowly rerelease water; and in granular form, it keeps soils relatively loose once it's mixed in. The team tested the approach on seedlings and found faster germination and higher growth rates among wheat grown in a soil-biochar mixture, compared with plants grown in biochar-free soil. The group says it is looking for ways to mass-produce biochar relatively cheaply and is undertaking long-term field studies to see how well this approach works on vegetables and other crops.

The researchers – one of several commercial and university-based groups exploring the potential for biochar – reported its results at last week's annual meeting of the American Chemical Society.

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