Topic: Why is my topsoil more determinedly claggy than my subsoil?

[Vinlander]

I'm on heavy clay, but I find that lumps of my subsoil (even yellow clay) left on the surface over winter will weather nicely to crumbs.

However dark, fertile-looking lumps of topsoil left in identical conditions don't - in fact they harden to adobe as soon as they dry out.

Is this the fertiliser-created claggyness I've read about in L D Hills books?

He says that old KCl fertilisers were the worst for disturbing the ionic balance of the soil.

Will anything else cause this? Is it just CO2 making the topsoil less alkaline?

I will be treating it with Gypsum at some point but it would be nice to know how to stop it in the first place...

Cheers.

PS. I will also try pulverised plasterboard in a controlled experiment - the price of Gypsum is crazy - it's more expensive than the plaster of paris made from cooking it!

[Ian Pearson]

The gypsum should help a bit to aid flocculation.
How much organic matter is there in the topsoil? My first suspicion would be that there are low levels. If the soil is dug annually most of the humus will be burnt off after 5 to 7 years unless you are compensating for the effect by adding large amounts of compost.

[Vinlander]

I haven't had the plot long and I'm not sure how much or recently it was manured or limed - it certainly has a very wide range of humus contents - even the odd horse egg is visible in the best bits.

I'm fairly experienced in dealing with heavy soils in this locale - it's based on yellow clay, and I'm pretty confident that the colour of this soil is a good indicator of the amount of humus.

The problem exists in everything except the darkest bits.

I wouldn't expect this topsoil to be as claggy as it is (except maybe the palest sections), but I've had limited experience with subsoil (it's closer to the surface than I'm used to) - I'm particularly surprised by how well it weathers.

It may be that the helpfully crumbing subsoil is by far the most unusual of the two aspects...

[Ian Pearson]

It's a strange world when you start using subsoil as a soil improver!  ;D

[Vinlander]

It's a strange world when you start using subsoil as a soil improver!  ;D

Yes, it's tempting to use it to create a tilth for sowing - crazy!

I'm pretty sure lime or gypsum will solve the problem but the contrast between the two soil types has left me scratching my head...

Cheers

[amphibian]

It's a strange world when you start using subsoil as a soil improver!  ;D

I used to work clay over a sand subsoil, the subsoil certainly aided the crumb of the topsoil when mixed.