Allotments v Farms

I think 1kg per square metre is very achievable, especially if you're getting more than one crop out of the space per year i.e. spring, summer and winter harvests.

Crops which I know give me more than that:

garlic - 2kg/sqm
potatoes (in pots) - 10+kg/sqm
tomatoes - 13kg/sqm (1.8 sqm border in the greenhouse produced 24kg of tomatoes, if two hadn't died early it would've been closer to 30kg)

Lighter things like leaves don't give you much all at once but spread over a long time I bet we're getting well over 1kg of lettuce from two trough planters. It would be interesting to track everything but honestly I'd give up a few weeks in 

I would love to track it all too - but can't be bothered  I would like to know how many kilos of gooseberries the birds ate too!