What is the current situation of research efforts on the sorptive
properties of turfgrass thatch in the U.S.? Are there many scientists
working towards better understanding this specific topic? Very much
appreciated will also be a list of researchers investigating turfgrass
thatch sorptive properties. Thanks!!

There's a center for Turfgrass science at Rutgers. The symposia notes
may be of interest to you.

http://turf.rutgers.edu/

You also get quite a lot if you do a GOOGLE Scholar search for:
"sorptive properties of turfgrass"

Thank you, dops-ga! Yeah, Rutgers has a famous turf program. 
;-)