Is there any item which boosts the power of Ground-type moves?

Question

Like Poison Barb for Poison-type and Magnet for Electric-type

Answer 1

Earth Plate: Boosts the holder's Ground-type moves by 20%
Ground Gem: One-time use; boosts a Ground-type move's power by 50%
Groundium Z: Upgrades damaging Ground-type moves into Tectonic Rage; turns status Ground-type moves into their respective Z-Moves
Soft Sand: Boosts the holder's Ground-type moves by 20% (10% in Generations II and III)

Ground-type items (Bulbapedia)

Answer 2

Soft sand can boost its power.

Locations

diamond/pearl/Platinum-Mt Coronet

HG/SS-blackthorn city (santos on saturday)

RSE-route 109 (a gift from the youngster)

Answer 3

Soft Sand and Earth Plate both boost Ground moves by 20%.

Comments

A Ground Gem will boost the power of a Ground-Type move by 50%, but only once.

Answer 4

Earth plate-oreburgh gate

           -the underground