What is the measures in controlling land degradation

land degradation can be controlled by gardening, conserving tillage, using fertilizers, and constructing wind breakers

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.