Earth's recent climate spiral.

[The Grand Nudger]

The amount of carbon they released in the making of terra preta was impressive for Stone Age population, but trivial next to the current industrial rate and volume of release.    The self-regenerative properties of terra preta greatly contributes to lowering the amount of initial burning needed to get the process started.

- Similar ancient and eco-friendly ways of agricultural production are present in many parts of the world. In fact at the beginning of the century all agricultural methods were traditional and quite similar to this “terra negra” method of agriculture.
    Of course more modern agricultural methods have increased agricultural production a lot. So we cannot seek to totally eliminate modern methods of agriculture. But the issue is this:
Rectangular agricultural spaces, with chemical fertilizers and intensive agriculture are gradually becoming sand. Sand is when there is no biomass left in the soil. So you have to put even more chemicals and even more water into it in order to be able to grow anything in this type of soil.
   The alternative to this is to have soils with at least 3% of organic material in it (living organisms and to have trees around agricultural fields that will reduce erosion, create some shadow (that will protect these organisms) and attract and trap rainwater. With such soils you need less irrigation and much less pesticide and fertilizers. I think this should be the new method of agriculture because even in much religious societies like India the number of farmers committing suicide has increased a lot in this century.
   So this is one of the many methods that are available to us even we are to keep inhabiting this spaceship of ours

Slash and burn is not eco-friendly.  

If we wanted to point to an eco friendly form of traditional agriculture (that will feature heavily in future) we need look no further than the chinampas system also used in those same slash and burn areas and cultures.  We need to come to terms with the fact that we will need more food than even the well managed soils of earth (dwindling at present) can sustainably provide.  This started out as floating beds of vegetation, but today has morphed into massive zero discharge systems pulling in 17m3/hour at 99.6% reuse efficiency capable of producing over 500 tons of animal protein and many, many more in edible or useful vegetative and fruiting mass which require no fertilizers, pesticides, or antibiotics whatsoever (in fact, can't operate -with- them).   With more green energy available every year - excess sustainable productivity can go to processing the nutrient mixes and provide lift far beyond what we generally find available today, to the point that they're suitable for the fine delivery lines of scalable vertical systems..which, even on the low end, can increase the productivity per acre of many important crops by as much as 200-800%.  Freeing up field acres for even more staple crops under no-till management and livestock as regenerative agriculture. All of which leading to greater soil and water conservation, reduced hunger, increased wealth, and lower carbon footprints.

This is something we can do today, no future tech or future discoveries required.  It's already economic at scale, but, at least for now, with capital investment high and the price of oil very intentionally kept low, it struggles at the scale of the small and/or family farm.  Thus, the epa and the nrcs in conjuction with the usda and land grant college system have pumped tons of money and research and volunteer work at steering future investments and developments into operations like this, and out of what we will soon no longer call conventional ag.