The short answer - YES you need to till/blec new infield mix into the existing mix. Why? The laying of the two material will cause an interface that will cause poor conditions when the infield is saturated. Here are two photos:
An infield that was not tilled.....
This photo was taken from an infield in Ohio this past week. The superintendent said, "The infield played well until this spring, now it is our worst infield!" As you can see, there is a layer in the profile. Keep in mind, blending infield mix with a harley rake WILL NOT work to properly blend a profile.
An infield that has been tilled.....
This photo is from 5/3 Field in Dayton, OH. This is a great shot due to the fact that there is no layering present, and it also shows the sand below the infield mix. This is common on sand based baseball fields.
So, how do you add new infield mix to an existing infield? Follow the link HERE to find out.
Go to j-dturf.com to learn more about J&D Turf.