06. Biochar: application and incorporation

Preparation
For these trials, there is no need to prepare the biochar before application, since it is already a small uniform size. If the biochar was fines from charcoal for example, it may be necessary to crush some of the larger pieces, to make it easier to spread.

Timing
It was noticed that the ash from the brick factory was very dusty, and from this experience adding on a windy day is not recommended. Biochar which is moist would not blow away, and for biochar from the SME gasification units in these trials, it is possible to choose fresh biochar which is still moist from the process of washing out the biochar from the unit.

Application
It is recommended that the method of application fits in with the technological constraints which are already occuring in the area. For example where land is hand dug (most likely to be small scale farms), the bags can also be spread on the land by hand also. Where the farm is large scale mechanical means can be considered appropriate. This has not been used for the trials in Cambodia since most of the areas are small sized.

Biochar should be applied at a time in the system when it will not require extra effort for incorporation, for example before final plough. At the Sangkheum Centre – the biochar was added at the same time as compost and manure application, so no extra incorporation was required.

Incorporation for trials
Where biochar is being applied to rows for the trials (this makes monitoring easier than plots which cover multiple rows), but the farm is ploughed by ox, it is incorporated by hand to avoid dragging the biochar across the rows. Ploughing is generally done by oxen or very occasionally hand driven mechanical plough (picture to follow…) for large fields.

Depth of application
Biochar should be incorporated to no more the depth of the roots of the crop being grown. It is easy with a hoe (in well tilled soil!) to incorporate to 10-15cm which is sufficient.
For tree crops it may be more appropriate to add the biochar to the hole which is dug before planting – in this project tree crops are not being tested.

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