Posted: 08/02/2014 at 22:32
Any bulky organic matter like this will help in the long term but anything uncomposted like wood chippings will deplete the nitrogen levels in the soil (as nitrogen is taken in as they decompose), so plants will not grow very well for a year or so if you dig it in fresh. Much better to compost the chippings first, adding as much green matter as you can lay your hands on to provide the nitrogen required for them to decompose. You can also add other high-nitrate sources such as urine or high-nitrate fertiliser as a compost accelerator.
I think raised beds are an excellent solution for a clay slope though and you can use them to terrace the slope, making it a much more useful area to grow things in.