Planting dilemma

A few years ago, to supplement my growing space I "liberated" a piece of land on our property. It's about fifteen metres by 15 metres and good rich soil that has had tons of horse muck on it over the time I've been using it. Problem is it's heavily shaded by trees and only really gets full light in the early morning and late afternoon/evening. It's heavily infested with mice, probably due to the cover given by the trees so peas and beans just get dug up. Carrots get murdered by carrot-root flies and brassicas get mauled to death by wood pigeons. The only crops that seem to do well there are spuds and parsnips and therein lies the problem.

This summer will be the fifth successive crop of spuds off it. They appear quite healthy and vigorous, probably due to the amount of muck applied and in fact the only legacy problem I seem to have is the vast amount of "volunteer" spuds that I have to deal with every year.

If I am to keep on growing spuds on it is there any necessary remedial or other work I need to do to the soil which until the copious amount of horse manure was added was heavy clay? I'm reluctant to abandon it back to nature

I should have added that at planting time I use a modest amount of "Growmore" in the drills

Yes, I know that I'm constantly using the same nutrients Yorkie but I wondered if all the manure plus the Growmore would replace them. I also wondered if liming might be beneficial

There's no sign of a build-up of diseases and pests yet but I agree it's likely to happen at some time if I plant spuds year after year.

I'll try brassicas with protection on half of it

Ironically, another adjoining similarly shaded patch of land that I rescued from nature supports a prolific crop of black, white and redcurrant bushes plus gooseberries without the need for any protection provided I pick the fruit as soon as it is ripe

Thanks, good advice