We often receive requests to adding biochar to the vermicomposting process to increase the value of the vermicast or the process itself. Most papers I found to this topic are actually finding that biochar hardly ever adds value to vermicast but vermicast almost always adds value to biochar. I would like to see a comparison of the products as single product (controls) and as of combination and to understand where the value adding aspect is.
As the quality of the compost vermicast and biochar varies a lot we need to compare high quality products against each other. Using a low grade compost and a high grade biochar will of course increase the compost quality (even sawdust might do so). But on the other and a high valuable biochar might be 'misused?
Regarding Terra Preta which is used as a referent for the value of biochar. These soils are high in nutrients, biochar, and earthworms (vermicast). What exactly is adding how much value to the soil fertility?
@ Michael, its a good question. If you look at biochar, it is highly porous, lightweight, fine-grained and has a large surface area. Approximately 70 percent of its composition is carbon. The remaining percentage consists of nitrogen, hydrogen and oxygen among other elements. On the other hand, compost usually vermicompost a worm castings are very important to the fertility of the soil. The castings contain high amounts of nitrogen, potassium, phosphorus, calcium, and magnesium. So, both are adding value in different way to the soil. Therefore if you can mix both then it would be fantastic.
For sure, compost to biochar , in order to create two different dynamics of nutrient release kinetics to meet short term supply and long term supply . And till then , short term supply of nutrients is over , biochar will display its amendment effect indirectly triggering the better nutrien supply chain . Perhaps , this is the biggest limitation with biochar , it doesnt cater to plants immediate nutrient requirement , besides high dose of biochar currently being recommended.
In terms of adding value to compost vermicompost is the best option.
Both compost and biochar can have issues with slow nutrient availability. The use of vermicompost which is readily available as a starter nutrient is particularly useful for addition to either compost or biochar which have great physical properties but issues in readily available nutrient content.
The classic work at Ohio State University show that using 10 to 20% vermicompost can raise the potential container tomato production up to and over 50% compared to a growth mixture without the vermicasts.
I would suggest that grower try incorporating 10 to 20% vermicompost in the leaf compost as a optimizing strategy for high value horticultural crops.
Do your own trials to confirm the results under your own condtions.
Compost and biochar can be limited for availability of micronutrients in neutral and alkaline growing media.
Properties of biochar depend upon the raw material and the temperature of pyrolysis during its production. Thus, its sole application or integrated application with vermicompost may give variable crop growth response in different soil. There are conflicting reports on combined effect of biochar and VC. In llettuce sole application of biohar and VC have shown positive effect on plant yield and crop growth but combining biochar with compost did not result in synergistic and summative effect. Contrarily, in rice, combination of biochar and moderate dose of VC improved the rice yield due to reduction of ammonia and nitrous oxide emission. Thus, It is advisable to conduct your own experiment to confirm the response on soil properties and crop yield.
Please go through these articles
http://doi.org/10.1155/2017/3158207
Pedosphere, 2019. 29 (1): 82-94
Biochar co-adsorb organic pollutants along with native organic matter in the soil. Biochar also may cause secondary pollution. It is necessary to maintain soil organic matter for higher crop yields. So, I suggest to add biochar(less quantity as additive) to suitable compost (more quantity). It gives more total nutrient value to the each other.
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