When it is added to soil, biochar has generally been shown to be beneficial for growing crops; additionally biochar contains stable carbon (C) and after adding biochar to soil, this carbon remains sequestered for much longer periods than it would in the original biomass that biochar was made from. Crop yield improvements with biochar have been demonstrated repeatedly for acidic and highly weathered tropical field soils (Lehmann et al., 2003; Rondon et al., 2007; Steiner et al., 2007; Kimetu et al., 2008), and there is new data on biochar use in temperate soils of higher fertility (Laird, 2009; Husk and Major, 2010). While many reports on biochar trials exist in the scientific literature, the practice of applying it to soil in commercial farm or other “real life” operations is just beginning, and no widely accepted guidelines currently exist.
Biochar should ideally be applied to an area of soil that tree roots will eventually utilize to take up nutrients, i.e. the “drip line”. The drip line refers to the area you would get, once the tree has reached its mature size, if you drew a circle on the soil corresponding to the size of the tree’s crown. To apply biochar to the entire drip line it is necessary to work it into the soil beyond the tree’s planting hole, and this is not always possible. Here we describe different ways of applying biochar when establishing trees.