Because rice is such a different crop than wheat or barley, there are a lot of differences in the way that rice cultivation shapes the countryside. […] The thing to note about rice is that it is both much more productive on a per-acre basis than wheat or barley, but also much more labor intensive; it also relies on different forms of capital to be productive. Whole-grain wheat and brown rice have similar calorie and nutritional value (brown rice is somewhat better in most categories) on a unit-weight basis (so, per pound or ton), but the yield difference is fairly large: rice is typically around (very roughly) 50% more productive per acre than wheat. Moreover, rice plants have a more favorable ratio of seeds-to-plants, meaning that the demand to put away seeds for the next harvest is easier – whereas crop-to-seed ratios on pre-modern wheat range from 3:1 to 10:1, rice can achieve figures as high as 100:1. As a result, not only is the gross yield higher (that is, more tons of seed per field) but a lower percentage of that seed has to be saved for the next planting.

At the same time, the irrigation demands for effective production of wet-rice requires a lot of labor to build and maintain. Fields need to be flooded and drained; in some cases (particularly pre-modern terrace farming) this may involve moving the water manually, in buckets, from lower fields to higher ones. Irrigation canals connecting paddies can make this job somewhat easier, as can bucket-lifts, but that still demands moving quite a lot of water. In any irrigation system, the bunds need to be maintained and the water level carefully controlled, with also involves potentially quite a lot of labor.

The consequence of all of this is that while the rice farming household seems to be roughly the same size as the wheat-farming household (that is, an extended family unit of variable size, but typically around 8 or so members), the farm is much smaller, with common household farm sizes, even in the modern period, clustering around 1 hectare (2.47 acres) in comparison to the standard household wheat farms clustered around 4-6 acres (which, you may note with the yield figures above, lands us right back at around the same subsistence standard).

Moreover, rice cultivation is less soil dependent (but more water dependent) because wet-rice farming both encourages nitrogen fixation in the soil (maintaining the fertility of it generally without expensive manure use) and because rice farming leads naturally to a process known as pozdolisation, slowly converting the underlying soil over a few years to a set of characteristics which are more favorable for more rice cultivation. So whereas with wheat cultivation, where you often have clumps of marginal land (soil that is too wet, too dry, too rocky, too acidic, too uneven, too heavily forested, and so on), rice cultivation tends to be able to make use of almost any land where there is sufficient water (although terracing may be needed to level out the land). The reliance on the rice itself to “terraform” its own fields does mean that new rice fields tended to under-produce for the first few years.

The result of this, so far as I can tell, is that in well-watered areas, like much of South China, the human landscape that is created by pre-modern rice cultivation is both more dense and more uniform in its density; large zones of very dense rice cultivation rather than pockets of villages separated by sparsely inhabited forests or pasture. Indeed, pasture in particular seems in most cases almost entirely pushed out by rice cultivation. That has very significant implications for warfare and I have to admit that in reading about rice farming for this post, I had one of those “oh!” moments of sudden understanding – in this case, how armies in pre-modern China could be so large and achieve such massive local concentrations. But as we’ve discussed, the size of an army is mainly constrained by logistics and the key factor here is the ability to forage food locally, which is in turn a product of local population density. If you effectively double (or more!) the population density, the maximum size of a local army also dramatically increases (and at the same time, a society which is even more concentrated around rivers is also likelier to allow for riverine logistics, which further improves the logistical situation for mass armies).

But it also goes to the difficulty many Chinese states experienced in maintaining large and effective cavalry arms without becoming reliant on Steppe peoples for horses. Unlike Europe or the Near East, where there are spots of good horse country here and there, often less suited to intensive wheat cultivation, most horse-pasturage in the rice-farming zone could have – and was – turned over to far more productive rice cultivation. Indeed, rice cultivation seems to have been so productive and suitable to a sufficient range of lands that it could push out a lot of other kinds of land-use, somewhat flattening the “ideal city” model that assumed wheat and barley cultivation.

Bret Devereaux, “Collections: Bread, How Did They Make It? Addendum: Rice!”, A Collection of Unmitigated Pedantry, 2020-09-04.