I live and work in the northwestern province of Battambang, Cambodia. My wife and I started a small farm in 2017. We are preparing to plant roughly 85 fruit trees (longan, durian, jackfruit, mango, orange/lime, guava) on very flat ground. The soil, however, is not good, to say the least. First, the top meter of soil is from soil taken out of the ground when digging a pond in 2018; very few weeds even grew in that soil during the 2018 rainy season! Second, even the original soil—the soil that was covered with the pond digging soil—was severely degraded after decades of rice growing using a stew of chemical inputs, being left exposed during the hot season with no vegetation, and continuous deep plowing.
So, I am seeking advice on how to plant fruit trees in such poor soil?
Additionally, whatever I learn from my farm will be passed on to the NGO I work for. We have an organic market garden project, but we have not done work with fruit trees.
I would really appreciate any advice that might be given!