This is a rhetorical question. It can also be translated as "It cannot be made salty again" or "No one can make it salty again." (See: [[rc://en/ta/man/translate/figs-rquestion]])
## for the soil or the manure pile ##
"Manure pile" can be translated as "compost heap" or "fertilizer." Manure was used to fertilize gardens and fields. Food that had gone bad could be mixed in with manure. But salt that had lost its flavor could not be used even for that. It was completely useless.
## He who has ears to hear, let him hear ##
This can also be translated as a command: "If you have hears to hear, listen well" or "If you hear what I am saying, pay attention."
## He who has ears to hear ##
“Whoever can hear” or “If anyone hears me”
## let him hear ##
“let him listen well” or “let him pay attention to what I say”