Good to know about the project you are doing. But, if you want to connect any board to Blynk, you do need some kind of internet connection, unless you are trying to run it on a local server.
And HC-12 module is basically used for communication between two arduino devices. It won’t help you in connecting to the internet.
And I think the reason you are using an HC-12 module is just because the place where your arduino located, lacks Wi-Fi connection. So, let me solve this problem by simply giving an example.
Assume that in the farm, there is a location, where the boss arduino is located with the HC-12 module.
And there are other arduinos around the farm from where they send the data like moisture, humidity, temperature etc. to the boss arduino. And the boss arduino will have the wifi connection to interact with Blynk server.
Instead of using Boss Arduino, you can use ESP8266 which already has Wi-Fi built in. And this time you don’t need to use the pins of the ESP. This would be an easier solution for you.
Using the combination of ESP & Arduinos like this, you can take advantage of long range data transmission of HC-12, and you will stay connected with Blynk as well.
Tip - You can use specific IDs for the other arduinos to specify, which arduino is sending data to the Boss ESP/Arduino. This will help you show data accordingly on the Blynk app.
Also, you can refer this video to get help in connecting HC-12 with Arduino