What feature is essential for a spray tank to effectively function?

For a spray tank to effectively function, a critical feature is having an opening for filling. This is essential because the tank must be able to receive the liquid that will be sprayed onto crops. Without a proper opening for filling, it wouldn't be possible to load the tank with the necessary pesticide or nutrient solution before application, rendering the entire operation ineffective.

While options such as adjustable spray nozzles, a filter system, and a specific capacity can enhance the efficiency and versatility of the spraying process, they are not fundamentally necessary for the basic operation of a spray tank. The opening for filling is the primary design component that enables the tank to be used, making it indispensable in ensuring that the tank can be filled with the treatment solution required for pest management.