I often add rice husks to potting mix to help with drainage and in the belief that when they finally break down, they add some organic matter to the soil. I was wondering what, if any, is the difference between the normal chaff and that which has been burnt (แกลบดำ)? 

Also, would it be good as a mulch? 

My wife add it to her mulch.

2 hours ago, khwaibah said:

My wife add it to her mulch.

I'm wondering about using it as mulch on its own. 

1 minute ago, djayz said:

I'm wondering about using it as mulch on its own. 

 

She add s rice straw, rice hulks, cow chips with some earth, water it cover up let ferment.

I'm guessing that the decomposition of rice husks would involve removing nitrogen from the surrounding soil. Not a big deal in view of the rather light weight of the husks but worth keeping in mind. Carbonised rice husks seem to get used in making potting mixtures and likely don't use up nitrogen.

Raw hulls contain lignin which is slow to decompose. It is burnt off during the carbonisation process as are volatiles leaving effectively charcoal. This will effect the C::N ratio and increase pH levels and act similarly to liming.  CRH also acts like a normal carbon filter and provides a home for microbes.

Note CRH will effect the nitrogen levels with excess carbon reducing the nitrogen content. The trick is to get the balance right. As nitrogen is lost quickly in composting (leeched and volatised) having a high level of carbon at the start will assist in trapping the N in plant useable form given microbial activity is present.