For me RS485 transceiver is the 8 pin integrated circuit (see MAX485 as an example).
From your Moisture Sensor tabele I understand that it already has transceiver inside (it not outputs TXD and RXD lines that you would have to convert (using RS485 transceiver) to RS485 A, B lines.
So you not need transceiver.
But I think at last I understood what you write.
Even we use RS485 since 90s about Modbus I know practically nothing (only heard that name and imagine a little what it is).
So not assume what I write as being certainly true. According what I know (not sure) I think Modbus is stupid communication protocol that forces system to use on transmission much more energy than it is really needed. As the whole world is trying to limit the energy consume I am against using RS485 this way.
In our RS485 use device sends something only when it has something to tell and not have to answer 50 times a second that it has nothing to send (I think, but not sure, Modbus works that way).
So:
- RS485 is the physical specification of connection,
- Modbus is one of possible communication protocols.
I don't know these devices you name transceiver.
I can suppose that those of them that call only RS485 allow to communicate through them in any protocol so if Modbus is needed it then have to be realized at PC using this transceiver.
It is possible that those of them that have Modbus in specification realize that protocol themselves so at PC connected to them you need not to worry about Modbus protocol itself.
You should read these transceivers detailed specification to understand what they offer you.