You'll need to refer to tire inflation charts in your tractor's operator's manual for the recommended inflation for your tractor weight and tire size. Recommended inflation levels may be as low as 6 to 8 psi. Consider using larger tires or duals if you must inflate radial tires over 14 psi to meet their weight carrying capacity . Larger tires are better. You'll gain a larger footprint, resulting in reduced ground pressure, along with the ability to carry more weight at lower inflation pressures.
Iron is better than liquid for ballast.
Iron weights can be added and removed more easily than liquid ballast to help you fine-tune your tractor to the task. Liquid ballast makes sidewalls stiffer, which causes a rougher ride and more compaction. It also increases rolling resistance. Use iron wheel weights and suitcase weights to get the ballast you need. A bit of slip is good.