How should smallholdings be mapped as a landuse?

I do not understand the difference betwean a smallholding and any other farming. It is common for farms to produce a mixture of foods, and for their own consumption as well as for cash.

Note that a crop field in someones back yard does not make it a farm. If the primary use of the area is for living and seccondary use is for crops then it is a residential area. This goes the other way so if the primary use of an area is for food production but there is a farmer living on the lands then it is a farm (with a farmyard).

I do not exacly know what you are describing but you are not describing anything different from a residential area where it i common for people to grow crops in the back yard. In that case you should use landuse=residential

I did some on-ground mapping ins Sub-Saharan Africa and also stumbled across this issue.

The basic problem ist that you often find yourself in areas which have a mulitfunctional landuse (typically living, some subsistence or even cash-crop farming, some small shops, often scattered forested or scrubed areas, etc.). Besides the mosaique nature of the landuse pattern, these landuses are often highly dynamic on the temporal scale. Particularly in urban areas (like it is the case on your image) the mosaique of landuses changes very rapidly and typically becomes more and more residential.

So we basically have a complex landuse pattern to map, and to my opinion it is not a matter of a missing landuse-tag. Once a suburban dwelling moved from highly multi-functional to residential it seems clear that the landuse=residential would be appropriate. A multi-functional landuse pattern may only be represented by the mosaic of tiny landuse pockets here and there but besides being complex you are also running the risk that it will be outdated rapidly.

As others have said, it's probably not a good idea to propose some new tag for this. Personally I'd call this whole area farm land. Clearly it's interspersed with little patches of land area which could be mapped in a very finicky way to try represent residential bits. There's also a wondrous variety of tags for different crops / orchards, ...if you had the time for that sort of thing.

We can generalise this question to "How itty-bitty and fine-grained should landuse areas be?". And this is a tricky question. We have it listed here as an open question which applies equally in other situations. In a city we have to decide if a corner shop in the middle of a residential area needs to have it's own little patch of landuse=retail.

My opinion: land use mapping has to involve some level of broad brushstroke simplified classification. Increased detail only comes when you start mapping individual buildings. But that's just the way I see it, and of course other mappers come along and add details anyway. So for example I wouldn't have bothered with this pink patch, but I'm not sure how I would justify deleting it, now that it's been added.

A lot of tagging questions can be settled by thinking "what is this thing primarily?" (same for classifying different types of shop in a city for example). So is this land area primarily farm or residential? I'd say farm.