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If the soil we have has pH 7,2 and we want to add this fertilizer which has 15-0-15 (NPK). What should the fertilizer contain in order for the pH to get reduced?

I believe that $\ce{K+}$ ions should derive from $\ce{KCl}$ because it won't affect the pH.If it comes from $\ce{K2SO4}$, the soil will be more alkaline. I'm confused about the nitrogen. Should it come from urea or NH4NO3? I believe that if the ions come from urea it will be more alkaline. Or should it come from $\ce{(NH4)2SO4}$?

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  • $\begingroup$ This Wikipedia article has tables of different fertilizers and their composition with respect to their NPK content. For example, the fertilizer sylvite is a naturally occurring mineral of KCl that is 0-0-63. Most of the fertilizers are of course synthetic mixtures. Also note that the value for P is reported as $\ce{P2O5}$ and K as $\ce{K2O}$. K and P are not actually present as these species, this is just a convention for reporting their values. This doesn't answer your pH question directly, but I'd still check out the above link. $\endgroup$
    – airhuff
    May 9, 2017 at 18:26
  • $\begingroup$ @airhuff Thank you! My question is on a theoritical level. I just ran into this question and I was curious and confused. The only reason I mentioned those compounds was because they were as choices. $\endgroup$ May 9, 2017 at 18:34
  • $\begingroup$ OK, I didn't quite get the context ;) What you've said about K and urea is correct, and the chemistry for the ammonium compounds is a bit more complex. However, if you read the Wikipedia pages for the ammonium compounds, I think it will be clear which one will be likely to acidify the soil. $\endgroup$
    – airhuff
    May 9, 2017 at 19:22

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