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Thanks for the information. Biochar is often about half the weight of compost or manure so 15% would be 7% by weight. Recommendations for co-composting (biochar+organics) are often 10-20% by volume or 5%-10% by weight. We have used up to 25% biochar by volume in soil-less media for growing seedlings.
In the Malawi case the 50:50 biochar-manure blend is likely placed into the soil with the seed so a small amount is probably placed in the soil in proximity to the seed. That is similar to techniques others have used where biochar is placed in a planting hole with seed and other amendments. If it is 50% by volume it should be about 25% by weight.
The composition of the char is also important. Biochars from crop straws and ag residues typically have higher ash content and therefore carry nutrients such as potassium and may have a higher liming effect. They are also slightly lower in carbon.
Coconut shell biochar has beneficial attributes which is why it is often activated and exported. Most of the organic based activated carbons sold in the US are from imported coconut shell. One biochar producer uses coconut shell biochar as a base for their formulated products.
What blends have others used? With what crops and in what soils?
From: tluds@Biochar.groups.io <tluds@Biochar.groups.io> On Behalf Of abraham abyslo
From our work on planting coconut seedling here in Nigeria,we have this ratio that consistently works:15/20/20/45 of biochar,compost,top soil and sand grains respectively.
Biochar from coconut shell is best in giving highest yield after charring.
On Sun, Jan 19, 2020, 14:45 Paul S Anderson <psanders@...> wrote: