There will be no "safety features" on that tractor! ;-)
But consider
It's not that the tractor won't start, it's that it will not turn over with the starter. It may very well start with a pull in gear or if it had a hand starter (It doesn't)
But
Your saying the battery is good, is not sufficient. How is it good? NEW and charged? Has it started other engines? Have you measured the voltage while the starter is activated? (should be 6.2V when not called on, and dropping to 4-5 V when the starter system contacts are made.
Are the battery terminals making good contact? Clean and tight? Can any of the connections be moved by hand? (bad)
The "click" is the starting solenoid. Hearing only the click is a sure symptom of either a bad battery (low charge) or poor connections.
There is even the possibility that the contacts within the solenoid are bad. Have you tried "clicking" 100 times to see if one time it "catches? (I have that issue with the bolens Solenoid, I just live with it, It always starts, I just don't know when ;-)
Me?
I would go through EACH connection between Ground, Battery, Starter solenoid, and starter to be sure everything was clean and tight (ther fact that you get the "click"confirms that the Key/ starter button is working.
I would also suspect the battery.
Check the voltage!
Sometimes, if the starter has not been used in a while, it helps to give the starter motor a jog using the methods Jerry has described. I just use jumper cables.
You can jump a 6V starter motor with 12V from your car or truck,, but don't let any lights, or the regulator remain in the circuit! Disconnect the big wire from the tractor to the starter motor or the Smoke will leak out!