I think at that point the phrase "engineered soil" loses all utility. We've been engineering soil with domesticated herd animals since prehistory, bringing fertilizer from pasture to arable land at the very least. If we look further at the most recent archaeological research on cultivation, there's growing evidence that soil engineering is how societies move from cultivation-assisted hunter gatherers to fully sedentary agriculture (and the strongest evidence, i.e. from extant isolated tribes in jungles, is that even the so called hunter gatherers participate in extensive soil engineering to support cultivation).