Biochar is a carbon-negative soil amendment shown to significantly enhance soil fertility and increase crop yields by retaining water, generating a conducive environment for nutrients, and creating a soil environment that allows microorganisms to work better.

Here are a few excellent works about biochar and its many applications published the Biochar Journal (tBJ):

How Biochar Works in Soil

The 55 Uses of Biochar

Terra Preta: A Model of Cultural Technique

Biochar in Poultry Farming

The Use of Biochar in Cattle Farming

Treating Liquid Manure with Biochar