> There are many places that are abandoned and barren because we did agriculture there.

Totally but I'd argue nowadays it's not because we are missing the knowledge but rather ignorance and short-term economic gains.

Imo sustainability goes hand in hand with population (and lifestyle). We want a diverse ecosyaystem, this simply doesn't work if there are 10 billion people wanting to eat meat or produce tons of plastic. Our problem is not knowledge in agriculture that prevents us from sustainable living.