Humus: difference between compost & colloidal humus
You may not be familiar with the term colloidal humus. In this blog we discuss what it is, why is it important, how to make more of it and how to use to improve your soil and plant container mixes
What is colloidal humus?
A brown-black coloured material that is found in compost and soils. It is vital to soil due to the following properties:
- It is colloidal in nature ie it holds water - up to 10 times its own weight
- It has a high cation exchange capacity (CEC) - typically 300-800 meq/100g
- It is ‘sticky and glue like’ - it aggregates other soil components (eg sand & clay) creating tilth
- It is resistant to biological decomposition - lasting typically 10-100 years but often 1000 years.
Colloidal humus is not...
Having defined what it is, it might help to know what is is often confused with. Colloidal humus (CH) is not compost – compost is 95-99% partially degraded organic matter that is typically 1-10mm bits. (This is often abbreviated to ‘POM’ within soil science). Compost (POM) decays typically in 1-2 years, Colloidal humus (CH) lasts 10-100 years, in some cases even longer.
Why is colloidal humus important?
Adding colloidal humus to your soil and container mixes will help you improve your soil to the best it can be. The improvement in soil fertility and tilth will give you more vigorous plants, vegetables and crops - and all in a sustainable manner.
Colloidal humus benefits include:
- Excellent soil water retention
- Excellent re-wetting
- Ability to hold and release NKP nutrients to roots
- Packed with trace nutrients (Ca, Mg, etc.)
- Improves nutrient supply to roots
- Reduces nutrient leaching
- Highest CEC value of all soil components
- Supports microbes and AMF-fungi
- Improves soil aggregation leading to improved aeration, ie oxygen flow to roots and microbes
- Long lasting - typically survives in soil for over 100 years
- Positive environmental impact: both humus & biochar sequest carbon and help offset carbon dioxide and hence reduce green house gases and global warming
How to make more colloidal humus
When organic matter decomposes in soil a tiny amount of colloidal humus is formed. Over time this builds up resulting in the soils we have today which contain anywhere from 0-5% with most averaging 1%. Composting (organic matter decomposition in a heap) also results is a tiny amount for new colloidal humus (1-5% by dry weight).
You can increase the amount of colloidal humus in your composting significantly by sprinkling the SoilFixer Humification Agent onto your new waste as it is added to the heap/bin. This powder increases the % colloidal humus to 30-40% (by dry weight).
How to use colloidal humus to improve your soil and plant container mixes
Once you have your “super” compost, you can add it to containers. You will notice pots and containers are revitalised as the nutrients are released. You will also find the potting mix resits drying out and absorbs and retains water much better. You just need to take care not to add to much as the water holding capacity needs to be balanced against the need for air spaces for essential root aeration. We typically mix shop bought compost 2:1 with compost made with the humification agent. We would aim to add the “super compost" to a clay based soli around 10:1 (10% by volume).
We will add more information on biochar, colloidal humus, composting and soil additives to our FAQ and blog in due course so please register for our updates.
Tony Callaghan, inventor of the patented HOTBIN composter, has authored many posts on how to compost and how to compost more effectively.