Now in pot experiments the most important point is to have the same number of plants per pot. To achieve this you plant more seeds and then you thin them after emergence to keep the same number of uniform plant per pot.
Now for calculating fertilizer rate of application in pots, you calculate according to soil weigh as you correctly indicated 2.2 M Kg/ha. You don't have to weigh the soil, just use the bulk density to calculate weigh from volume. Forget about space in pot experiment. you will have a lot of problems since pots have different shapes and forms!
Another recommandation mix soil and fertilizers for each treatment for the number of replicate pots. If you are using 5 replicates pot of 2 Kg soil/ pot, mix the fertilizers you want to apply to the 5 pots with 10 Kg of soil and after mixing well (preferably mechanically) distribute the same volume of soil in each one of the 5 pots.
If the amount of fertilizer to apply is small mix with some soil first and mix well before mixing to the whole soil. The idea is to have as much as possible, a uniform distribution.
You might also consider fractionating you nitrogen source if it will be leached.
Now according to the exact aim of your work other method sof fertilizationare possible.
Finally remember that maize is a mycorrhizal plant and this beneficial symbiosis can be influenced by the amount of soluble P you are adding.
Wishing you a lot of success in your work
hope it's help you
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