I want to ask about the increase in the percentage of something, but I am not sure what is the way to ask it in an interrogative way.
Can I say:
In how many percents does the yield increase if I water the trees every day?
I want to ask about the increase in the percentage of something, but I am not sure what is the way to ask it in an interrogative way.
Can I say:
In how many percents does the yield increase if I water the trees every day?
There's no such thing as 'a percent' - the word means 'in every hundred'.
You used the word percentage in your first paragraph. You can say By what percentage does the yield increase?