Chemical content of Composts – June 2022
As part of my upgarding of the nursery, we decided to investigate alternatives to ‘normal’ compost.
Whilst most compost suppliers do not add a chemical content breakdown on the bags, they may well give a PH value. Which is usefull in its own right, but it can be limiting.
This blog post came about, as we tried growing seed etc in the new compost. None grew, also trees that were potted, seemed very lacking in vigour.
The new compost was supposed to be a blend of composted chippings and amongst other things, green waste. We had purchased a tonne of this, only to find when it was delivered it was nothing like the pictute, and the smell was unbelievable. Now I am undeterred by the smell of cow manure and horse manure, which sometimes can smell quite sweet. My belief was that it has some sewerage waste, as the smell was vile. The heat was still being generated in the bag, and you could not touch it.
So we decieded to try and find out what was in it. We took samples at 2 different levels. We used a very basic test kit, not one that gives exact figures for NPK and PH, but more of a comparison.
We plumpted on a kit produced by Hanna instruments.
The tests give a range of colours, which are compared to a known colour range and readings. It was not too easy in getting a fluid out of compost. We had to mix distilled water with a quantity of compost, and then let it settle out. This did not happen, as nothing settled out, unlike a sandy soil. So we filtered and filtered using laboratory filter papers, till we got something that resembled a watery liquid.
Four test tubes were filled with different chemicals from out of the supplied sachets. Then a known amount of liquid was added. and then waiting a few minutes for things to happen.
TEST SAMPLE1
TEST SAMPLE2
In checking out the top image, it shows very high levels of N, P and K and surprisingly very high PH level much greater than 7
This resulted in us confirming that we had not got compost but ‘top dressing’. Top dressing being a high nutrient mix that is applied when plants are already growing or as a boost to ground during winter.
No good for seed sowing or where new roots are formed, as the high Nitrogen burns tender roots. It’s the old saying – never use any fresh manure, including chicken bedding.
However most finished composts are about neutral pH within a range from 6 – 8 with 7 being neutral and 8 is alkaline. Also composts commonly contain about 2 percent nitrogen, 0.5–1 percent phosphorus, and about 2 percent potassium.
As detailed at https://www.researchgate.net/publication/325554533_Chemical_composition_of_different_types_of_compost
Reference sources for further reading
http://www.carryoncomposting.com/416920214
https://www.hotbincomposting.com/blog/composting-and-ph-levels-in-the-hotbin.html