The next day she went out to visit the soil scientists, who were happy at her interest. They wanted to be able to feed themselves, and as more and more settlers moved south, this was going to be impossible without more soil. But they were finding that manufacturing soil was one of the most difficult technical feats they had ever undertaken. Nadia was surprised to hear this— these were the Vishniac labs, after all, world leaders in technologically supported ecologies, having lived for decades hidden in a mohole. And topsoil was, well, soil. Dirt with additives, presumably, and additives one could add.

No doubt she conveyed some of this impression to the soil scientists, and the man named Arne leading her around told her with some exasperation that soil was in fact very complex. About five percent of it by weight was made of living things, and this critical five percent consisted of dense populations of nematodes, worms, mollusks, arthropods, insects, arachnids, small mammals, fungi, protozoa, algae, and bacteria. The bacteria alone included several thousand different species, and could number as high as a hundred million individuals per gram of soil. And the other members of the microcommunity were almost as plentiful, in both number and variety.

Such complex ecologies could not be manufactured in the way Nadia had been imagining, which was basically to grow the ingredients separately and then mix them in a hopper, like a cake. But they didn’t know all the ingredients, and they couldn’t grow some of the ingredients, and some that they could grow died on mixing. “Worms in particular are sensitive. Nematodes have trouble too. The whole system tends to crash, leaving us with minerals and dead organic material. That’s called humus. We’re very good at making humus. Topsoil, however, has to grow.”

“Which is what happens naturally?”

“Right. We can only try to grow it faster than it grows in nature. We can’t assemble it, or manufacture it in bulk. And many of the living components grow best in soil itself, so there’s a problem providing feedstock organisms at any faster rate than natural soil formation would provide them.”

“Hmm,” Nadia said.

Arne took her through their labs and greenhouses, which were filled with hundreds of pedons, tall cylindrical vats or tubes, in racks, all holding soil or its components. This was experimental agronomy, and from her experience with Hiroko Nadia was prepared to understand very little of it. The esoterica of science could go right off her scale. But she did understand that they were doing factorial trials, altering the conditions in each pedon and tracking what happened. There was a simple formula Arne showed her to describe the most general aspects of the problem:

S = f(PM,C,R,B,T),