I wonder what proportion of the carbon in a plant comes from fertilisers vs CO2 taken in while growing? It looks like some fertilisers do contain carbon - but

I wonder what proportion of the carbon in a plant comes from fertilisers vs CO2 taken in while growing? It looks like some fertilisers do contain carbon - but not all. Eg ammonium nitrate doesn't, urea does. The ammonia tends to be produced using methane - so right now the fertiliser production process does produce vast amounts of CO2 (but that isn't carbon which goes anywhere near the cow). The CO2 from ammonia production seems solvable (assuming an abundant supply of non-fossil fuel energy) through the electrolysed hydrogen -> ammonia route. Would that be enough, or is the carbon locked up in minerals used in phosphate production also a major source of CO2?