[bobbyt]

My plot has still got parts where the soil is quite heavy and claggy. I've been treating it with various methods from horse manure to soil treatments, chicken pellets etc. About half of it is manageable now. I was thinking of laying cardboard on the other half (mainly because I have a lot of cardboard packaging to get rid of), and layering fresh horse manure on top of that over Autumn/Winter. Should I then cover that with sheeting or just leave open for nature to do its thing. Will the cardboard rot down in that timespan? Will this method be beneficial to the soil? Any helpful thoughts at all please.

[al78]

Leave it open, don't put sheeting over the manure. Yes the cardboard will decay over time, and will help suppress weed growth before it decays. The soil will benefit from the organic matter and the manure will help to dilute the clay. My soil is much better than originally after speading manure in the autumn and leaving it over winter.

[snowdrops]

The manure would compost down better in a heap 

[Subversive_plot]

Have you worked any lime or gypsum into that clay?

The reason the lime could be helpful has to do with a property of many clays to stay more open-textured and drain a bit better if the soil has plenty of calcium (magnesium, such as in Epsom salts, works as well).  Anything with sodium will do the opposite, tending to close the soil structure and decrease drainage.  Without delving too far into the details, this has to do with the structure of clay particles on a microscopic scale; sodium causes the clay structure to swell and close up, but calcium or magnesium can alleviate that problem.

I agree with snowdrops that compost would decompose well in a heap, or compost bin, but if you are looking for something to cover that cardboard over winter, do what al78 suggests, then dig it in next spring.

[Goosegirl]

When you're digging the soil get some grit or sharp (not builder's) sand and incorporate that in as a quick fix.

[Christine]

Don't be in a hurry bobbyt - it can take some seasons to really sort out proper clay.

[bobbyt]

Ok thanks for all the helpful replies. Had the plot about 6 years now, a big improvement over the years obviously, been using gypsum, poultry pellets, rotted manure, fresh manure, cardboard, and trenches for beans using uncooked kitchen waste etc, but still got some areas that are difficult to plant seeds in. It's great in some places, but hard work in others, especially after a dry spell like now. Maybe I'm digging up clay from underneath, but a no dig plot is a bit of a problem, as I can't get enough manure/mulch to cover the sort of depth you need for that. Perhaps I'll try again in small patches and see how it goes.