All your silos are filled to the brim.
This trophy is misleading, I am fairly certain that you can not fill your silos as I got well over 300k in each silo at one point. Based on when this trophy popped for me and what other people are saying my informed guess would be that you need 100-120K total for all 3 silos. This will highly likely come naturally when going for the platinum and again as with eco-farmer it's a quick and easy gold but resist the urge to go for this straight away. Follow the guide in the roadmap and only boost this trophy if you already have Pots of Gold. If it did not come naturally see Harvest King for boosting tips and make sure you drop off all crops at your silo.