Badly need help were using those three components But we have problem in Arduino ide when we run the code it always print the result but there is no value of the Nitrogen, phosphorus and potassium.
The advertising for those sensors is fraudulent. They don't measure N or P or K (which is impossible with only metal probes). They do measure soil conductivity and temperature.
Pointless exercise, those sensors are fake.
Show how you connected your hardware.
Show the code you are using.
Show your results.
This device becomes a good exercise in RS485 communication to transfer values from the sensor to the microcontroller and show the results. The results will be meaningless.
Can you clarify what you mean by the above. What results does it print? Perhaps you meant that the N, P, & K values were always zero?
Please provide the datasheet specific to your sensor - there are several NPK sensors that look the same but use different registers for their parameters.
As @xfpd says. A good exercise in RS485 Comms but that's about the limit of this type of sensors usefulness.