XXX fertilizer is an organic degradation that can produce non-smelly waste and increase the plant growth.
Is "non-smelly" appropriate?
If you mean that the waste has no smell at all, then you can use the word odorless.
If you mean that the waste doesn't have a rank smell, then you can use something like pleasant-smelling – if it has an odor that is pleasant. Otherwise, you might have to explain what you mean another way:
XXX fertilizer is an organic degradation that can increase the plant growth without producing the unpleasant smells of other organic waste.
"Non-smelly" is a bit awkward and not very specific, but it could be used.
However, "odorless" works better here, to signify not that it smells good (which is not usually particularly desirable), but that it doesn't smell much at all.
How about "that can produce neutral smelling waste"? Neutral would signify it doesn't smell unpleasant or pleasant. Just that it isn't odorless and the smell is pretty neutral smelling.
odor-free is commonly used in marketing material.