Biocar is a carbon rich resource which is a by product of waste management.

The material used for its development is wood, leaves or manures which are maintained in a heated enviroment of 200 to 700 C without oxygen to allow for burning.

This process is called pyrolysis.

This process can be engineered to produce renewable energy resources which are renewable.

Biochr is the solid remanent material with is used for soil amendment.

Biochar can greatly important acid infertile soils as found in yellow and red soil tropics.

Beside working to help lime the soil soil it opens the structure from its low density. In addition the spaces in the coarse texture give a living space orom beneficial soil microbes.

So the interest of biochar also comprises its ability to take excess carbon in the atmosphere and deposit it as a counteraction of greenhouse gases with increasing soil sproducitivty plant quality and stimulating the ecosystems.

The question is more complex and rich in concepts.

In my opinion, there is no great difference between these concepts which are related to the carbon. Biochar can be defined as the result of high carbonization in a special dispositive for improving the retention capacity of the soil as well as for limiting the lessivage process in this soil. Agrichar could be the biochar made for the agricultural purpose.

Pyrochar vs Hydrochar are related to the fire or the water which occured in the formation process of Biochar.

The nature of biochar is to expand niches for biological microbial communities. The physical spaces are habitats for these organisms to fix and abide. The role in an acid soil includes a liming effect. The alkaline nature of many chars can immobilize micronutrients in alkaline soil conditions. The carbon in soil can increase dramatically will biochar as the stablized pyrolized carbon can take thousands of years to decay.

The ability to increase soil organic matter levels can depend more on the resistance of the materials to decay rather than just the quantity.

Because the char conversion can yield a renewable energy resource but also it has the significant ability to sequester in the soil carbon which otherwise would reside as atmospheric carbon dioxide.