AHC/WI: Other River Valley Civilizations?

The problem with what you've quoted, and the example of the agricultural practices of my ancestors doesn't give claim to your conclusion that Mesoamerican strains of maize would drain the soil of nutrients just the same as more northern varieties of the crop. The comparison falls flat because there were larger and longer lasting urban centers from Central Mexico down to Nicaragua. So that's the evidence I'm looking for, not the reason why they failed in OTL and why my peeps had to move around once a generation. That's not what's being questioned.

And the draft animals were what? There were dogs and turkeys, and in some places semi-domesticated deer. Human feces was what was largely used for manure. These same practices and breeds of animals could all be acquired through a stable trade network being developed.
Good question. Certainly in Tenochtitlan they dug up lake mud and put it in floating beds for growing food, and that would restore nutrients to the land. What they did in relatively dry land farming, I don't know. Similarly, I don't know what the Maya did.

It's true that human manure, especially if you had wheeled carts/wheelbarrows to haul it around, could be used to fertilize fields, but I don't KNOW of any American (North or South) group that did that, but that may well be my ignorance.

We have two questions here, that I didn't really unpack.
1) nutrition of the food. Apparently the Mound Builders around Cahokia, say, didn't have beans, so there's an amino acid deficiency problem if you cant get other protein (e.g. game or fish, and there is very strong limits on how many people you can feed with wild game).
2) the other problem is fertility of the soil. Which again has a couple of prongs a) nitrates (dealt with by growing beans - the three sisters form of agriculture is very useful there) and b) minerals like potassium.

2a is well dealt with with the Mesoamerican or Haudenosaunee crop package. 2b isn't, and I don't know how the Mesoamericans dealt with it (aside from Tenochtitlan).

OK, a quick look at Wiki provides
One of the greatest challenges in Mesoamerica for farmers is the lack of usable land, and the poor condition of the soil. Several different methods have been used to combat these problems. The two main ways to combat poor soil quality, or lack of nutrients in the soil, are to leave fields fallow for a period of time in a milpa cycle, and to use slash-and-burn techniques. In slash and burn agriculture, trees are cut down and left to dry for a period of time. The dry wood and grasses are then set on fire, and the resulting ash adds nutrients to the soil. These two techniques are often combined to retain as many nutrients as possible. However, in the jungle environment, no matter how careful a farmer is, nutrients are often hard to retain.

and
However, the Aztecs created floating plots of land called chinampas. These were floating plots of mud and soil, placed on top of layers of thick water vegetation.
"chinampa" I think that's the word I was looking for.

What that article DOESN'T explain is how non-lake, non-forest agriculture restored fertility to the soil.
 

Driftless

Donor
Another part of puzzle for Mississipian Cahoikia, how did they deal with sewage and potable drinking water? With a population between 6,000 to 40,000, that becomes an enormous public health issue. For that matter, how did other riverine cultures deal with the issue?

The Mississippi itself would not resemble the current river much. The current river carries a lot of silt from agricultural runoff, in a more-or-less contained central channel. Even though there is a main channel now, the river is quite braided. Back then, it would have been mostly a collection of variable flow channels, some of which would near dry up in late summer. Then the upstream watershed would have mostly come off areas of glacial till, with some of the main stream flowing through a limestone & sandstone bluff area.
 
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