Fine top soil substrate compaction

HiNtZ

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I've decided to go with a minerlised top soil substrate and came across a nice tutorial on how to do that.

The only question I have is relating to a concern about the compaction of fine soil substrates.... I had the problem with the westlands aquatic compost that the first couple months were great, then the soil literally turned to a cement like composition where even my crypts roots couldn't bust through at all.

Is there any way that I can stop this happening? I'm only going with about an inch of soil capped with fine gravel and sand.
 

X3NiTH

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I am going to assume the cementing is a consequence of the CEC of the substrate sucking up calcium ions that are in excess (London water) and then reacting with phosphate dosing producing Apatite, the cross linking throughout the substrate as this forms will cause it crust.

I have made this assumption because I have observed this with the raw ingredients in a bag. I tried to save some time when preparing my water and spent a couple of hours one night making up little baggies of the required amounts of salts in it (about a six month supply), the B component bag as part of its makeup has Pottasium Phosphate and Calcium Nitrate (silly me had forgotten how reactive this compound is). I didn't find out until the second waterchange that the Calcium Nitrate (absolutely loves to hydrate and liquify freeing up the calcium) bound with the Phosphate making it completely unavailable. The little white rocks it formed were extremely difficult to crush (required a hammer) and would not dissolve even in excess of 40ppm CO₂ in the water storage container.

Maybe mixing the soil with something that's has a higher CEC to grab more of the free calcium would help and also that it has a larger volume compared to soil particle size so that it makes it harder for it to concrete together. No idea what would be suitable (can only think of sphagnum and LECA at the moment), maybe just mixing an inert sand through it would be enough to separate the particles enough to help prevent concretion.
 

HiNtZ

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The soil I was using before specifically was the westland aquatic pond compost capped with sand. The stuff was coming up in sheets after a year! The plant growth in the first 6 months was very good though.

IIRC it said that it was not suitable for lime hating plants so can only assume something went wrong in what you mentioned - I was dosing P very heavily also.

I may just mix some fine gravel into the top soil and see how it goes...
 

Tim Harrison

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It happens as part of the mineralisation process. The organic matter decomposes leaving just the clay minerals, and you're right it becomes a bit like cement.
I just let it mineralise in situ and add 1:1 moss peat, this maintains the structure of the compost for a much longer period. You can also add a few handfuls of grit as well, which also helps.
The added advantage for a low-energy is that CO2 is given off for longer and it may enhance the CEC of the mix.
 

HiNtZ

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Joined
26 Jan 2016
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578
Location
London
It happens as part of the mineralisation process. The organic matter decomposes leaving just the clay minerals, and you're right it becomes a bit like cement.
I just let it mineralise in situ and add 1:1 moss peat, this maintains the structure of the compost for a much longer period. You can also add a few handfuls of grit as well, which also helps.
The added advantage for a low-energy is that CO2 is given off for longer and it may enhance the CEC of the mix.
Does the peat moss have an effect on lowering soil PH though?
 

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