biochar is made by heating organic materials such as wood waste, crop residues, or animal manure to 350–500 ºC in the absence of oxygen. It has been advocated as a soil amendment because of its long-term carbon storage and because it has been shown to increase soil cation exchange capacity, water-holding capacity in sandy soils (see soil water), and biological activity (see soil biota). In trials in several European vineyards, the biochar had to be activated by mixing it with compost or manure. Despite early positive results, by the mid 2010s, no firm recommendations had been made for biochar use in viticulture, primarily because of the variation in commercially available products and their complex interaction with soil type, climate, grape variety, cover crop, and microbial activity.
