I'm no expert but I would guess it depends on what you are growing and how large of a plot you have. Are you talking about a home garden or a monoculture over many acres?
Excessive fertilizer is probably never a good idea.
It's not necessary to have a cover crop but I find it very beneficial.
I have been growing vegetables on the same 1000 square foot (50 x 20) space for 17 years with few problems. I put compost and some organic fertilizer on each year, mulch heavily with leaves and hay and in the fall plant winter rye as a cover crop over the winter.
Hope this helps.

I'm hoping to rent an allotment when I move to Sweden and I was wondering if it is worth separating into four sections instead of three, leaving one fallow which will be included in the rotation. Would it still be helpful on such a small piece of land?

Could you define what 'fallow' means to you a bit?
The term means different things to different people-
I could start going on about what it means to *me* and not help you a bit!

Whatever is best for the soil. I really don't know the exact definition as I'm new to gardening.

what size piece of land are you talking about?

I don't know the size yet, I would imagine a rented allotment is about the size of a small garden.

Many define fallow land as having been plowed but left unseeded. However, others of us think of fallow as a garden plot left to rest, and regenerate. That can include tilling the soil, if necessary, and seeding a cover/green manure crop to be turned back in to add some organic mater to the soil.
We are told, in the Bible, to let land remain fallow every 7 years so it can regenerate. Many of the older farmers practiced a 7 year rotation on the fields they worked, although seldom, from my conversations with them, was the field left barren and exposed to the ravages of the sun, wind, and rain. A green manure/cover crop of some kind was usually planted in that fallow field.
I find very little to nothing about leaving fields fallow today although many people do practice adding compost and other forms of vegetative waste regularly in the hope that would eliminate the need to leave land fallow.

I just try to keep feeding organic matter and rotating crops as best as possible.

â¢Posted by BrianW23 none (My Page) on Mon, Mar 24, 14 at 5:29

I don't know the size yet, I would imagine a rented allotment is about the size of a small garden

I'm guessing a small garden is "small" so I would say leaving part of it fallow wouldn't be a good idea. It would be just wasted space. How long are you planning on staying there?
If only a couple of years I would plant as intensively as you'd care to.

BrianW23 - I doubt you'll have space to leave a quarter fallow. If you make lots of compost, add muck and move your crops about a bit you don't need it. I've never seen (intentional) fallow areas at my allotments and I've had mine over 20 years. They are all crammed to the gunnels all the time.

I thought it would be a case of just rotating but I thought it was worth checking just in case. Thank you everybody. Darth_weeder - I'm planning on staying for life.

Perhaps this article might be of some use.

Here is a link that might be useful: crop rotation

As kimmsr's link suggests, crop rotation is of limited importance in a small garden Even if you move things around they are so close together that pests and diseases can travel from one area to another whatever you do. I just do a rough legume, brassica and 'other stuff' system but I don't sweat it if I have a space which needs filling or a plant which needs a home. They just go where they will fit.

A lot of diseases and pests, even the ones with the broad ranges, don't affect both grassy and broadleaf species. Therefore instead of fallow you can plan to use one section for monocot/grassy species of veggies, such as onions, garlic or corn. Not sure if corn will grow in Sweden though. Other sections can be used for dicot species.

Good luck in Sweden and tell us how the garden works out.

Thank you all for your advice. I'm thinking that rotating might be good for the soil anyway. I've still got plenty of time to think about that before I move.

Thank you darth - I'll let you know.