Answer:
Based on the other guys answer he clearly means reforestation (gardening).
Soil is a NON-renewable resource
And for the missing answer I think its groudnwater cuz its asking for a way to conserve soil fertilization. In the next sentence it says that organisms decomposition is the key to replenishing soil fertility so, if soil is encountered with groundwater it will be impossible for it to erode.
Step-by-step explanation: