For 15 years and above age apple / pear plants apply the following dosage of chemical fertilizers per plant. 
Potash     2.5  kgs                                
Urea          1.5  kg
DAP             750  gms.        Adding fertilizer to apple trees should be done 3 times during the growing season.

1. Make the first application (1/3rd urea, full DAP and 1/2 MOP) in early spring (preferably 15 days) before flowering. 
2. Make the second application (of 1/3rd urea) about a month later, after flowering is completed . 
3  And the final application (remaining urea and MOP) of fertilizer should be applied at the end of June, about a month after the second application under adequate moisture conditions.
Note, :  avoid any kind of hoeing, fertilizer application or pesticides spray during full bloom period.