Dear Kumar
I feed our palms here with Di-amonium phosphate in liquified form in our winters & also coconut palm fertilizer made specifically for 25 years plus aged coconut palm trees.Since these are all are chemical based use it only in trace quantities.i.e one regular spoon of fertz for 20 to 25 liters of water.And once the plams accept this then you can do this every 20 to 30 days.
And the white markings you see on those plastic pots are from camalin crayan pencils avaliable in all the local stationary book shops etc...
Love,
kris
Thanks Kris - at present I use a mix of clay and sun dried cowdung - it gives superb results - that too only before the mango fruiting season. But I will give this a try next month.