I'm taking a stab at this effect. Here's the result so far with hair for grass on a single patch using a vortex force (can't get anything out of the fan or constant(?))
Anyway, the obvious things are how the grass is all moving in a single block. Also, how it doesn't bend in an arc with the following through.
I've tried all the settings. Any suggestions?

The control splines affect the hairs on neighbouring patches so you could use more, smaller patches which would give you more control over localised movement and more variation.

Change the angle limits and maybe forces instead. Where is your vortex located?

Used fan and 15' angle limit.

more than one type of hair also

I'm trying to think of where you can change the hair type.....

The fan and vortex options are in the root force property list. Right at the bottom. Also I put a fbm turbulance on the force.

I think John is talking about adding more than one hair emitter with a different image or color to the hair system. Right click on hair system to add a new emitter.

After you've implemented the good ideas here, try using several forces and phsyically moving them over the grass for that localised gusty look.

Paul Forward did a pretty nice grass effect

http://www.hash.com/forums/index.php?showtopic=18781

EDIT: You have to save the .mov to disk and then change the extension to ".mp4".

Or there is this one that I did but it doesn't use forces:

Grass