Put me down in the never water a mango category. I haven't seen rain in a month and I still don't even think about watering mango. They do fine without it. Some of my trees are loaded with fruit. I haven't watered mango in 15 years. They don't need it and I think do better without it this time of year. Your mileage may vary, but i never water mine. Only time to water mango is when first planted. If you plant in the rainy season then you typically never have to water. Sure, watering won't hurt them, but they don't need it in my opinion. This is for East Central Florida. I'm in a severe drought right now and keeping the jaboticaba watered. But, Mango?!? LOL...never water them...
Put me down also in the never water a mango category, and fertilize only lightly. Of course, other climate conditions might require different culture.
My farm experienced a reasonably severe drought last year. The mangos, mostly 2 and 3 year old, came through the drought better than almost any other fruit tree I have. It's a s good as cashew.
The seedlings clearly have a significant tap root during their first year, but I don't know if that persists. I think the mango's drought resistence comes from it's ability to retain moisure in the leaves.