dictation doesn't (always) work under Safari

I am using Google Chrome and Safari from my brand new IPhone 6S. I switched recently from Android.

I use a website where I have to enter a lot of text, and I found dictation to be extremely advanced in IOS9, so I use dictation to enter the text.

Problem is, while it works in Chrome browser for IOS, the microphone button on my keyboard is grayed out in Safari on the same webpage.

This would not be a problem if I could use Chrome as my default browser, or if I could create an URL to be opened with Chrome on the homescreen, but due to Apple's policies, neither is available.

Can you help me? Why does dictation work in Chrome on IOS, while with Safari, the button gets grayed out (on the same webpage)?

Thanks,

John