How can i do this project?

MY PROJECT IS RELATED TO ELECTRONICS. I PLANNED TO DESIGN A SMALL HELICOPTER KIT THAT SHOULD SPRAY THE FERTILIZER OVER THE AGRICULTURE FIELD. I WANT TO CONTROL THE HEIGHT, AMOUNT OF LOAD IT CAN, and control the movement of the helicopter by a remote. how can i do this project?

You've created a long list of questions. The first and most obvious questions are:

What's wrong with a real helicopter to do the job?

How much fertilizer are we talking about?

Does it have to be a helicopter or could a fixed wing aircraft (i.e. airplane) or even a lighter-than-air aircraft be used instead? Helicopters are significantly more complex than either of the others.

In any case, I'd start with a scaled prototype. Go buy a remote control helicopter at a hobby store. Buy a radio control unit that has one more channel than you need to fly the helicopter. A good helicopter kit will require a four channel radio for flight. Buy a radio with at least 5 channels.

Design a scaled down reservoir for the fertilizer. A gravity fed distribution system is probably sufficient and significantly easier to design and operate. You will only need to have a switched valve to control whether the fertilizer can flow out of the reservoir. Use the extra channel on the radio control to operate a servo connected to the valve switch. You can buy a servo readily at a hobby store but will need to design your own valve switch.

Before taking off with your carefully designed prototype, make sure you know how to fly the helicopter. Even remote control models can be difficult to handle.

very carefully

There are already radio controlled helicopters that you can buy. However I don't know if it would be legal to fly a large version unmanned whereever you want?

oh wonderful project,, i think you must read more books about that,, just start by simplifing your request in to items and find each item answer