As is apparent in the terra preta, the addition of biochar can dramatically darken the colour of
soil, especially in soils that are low in organic matter. A relationship between soil colour and
low temperature fire occurrence has been demonstrated (Ketterings et al., 2000). Oguntunde
(2008) found soil at charcoal manufacturing sites to have 8% greater hue, and 20% higher
value and chroma. Since dark soils absorb more solar energy they may, depending on water
content and plant cover, display higher soil temperatures (Krull et al., 2004). This will affect
rate processes, enhancing the cycling of nutrients and potentially extending the growing
season in seasonal climates. In Japan it is a traditional farming practice to apply charcoal to
accelerate snow melt. Anecdotal evidence suggests more rapid crop establishment in
temperate soils enriched in char, but to date no quantitative relationships between biochar
application rate and these parameters have been reported. The study of Oguntunde (2008)
showed a one-third reduction in soil albedo in soils enriched in char. On a large spatial scale,
the application of biochar could affect the albedo of the Earth’s surface. Increasing surface
albedo has been proposed as a possible mitigation measure for climate forcing (Crutzen,
2006).