Try this:
public boolean onBlockActivated(World world, int i, int j, int k, EntityPlayer entityplayer, int par6, float par7, float par8, float par9) {
Item equipped = entityplayer.getCurrentEquippedItem() != null ? entityplayer.getCurrentEquippedItem().getItem() : null;
if (equipped instanceof Wand1)
{
world.setBlock(i + Facing.offsetsXForSide[par6], j + Facing.offsetsYForSide[par7], k + Facing.offsetsZForSide[par8], ModBase.nexussoil.blockID);
}
return true;
}
If not
public boolean onBlockActivated(World world, int i, int j, int k, EntityPlayer entityplayer, int par6, float par7, float par8, float par9) {
Item equipped = entityplayer.getCurrentEquippedItem() != null ? entityplayer.getCurrentEquippedItem().getItem() : null;
if (equipped instanceof Wand1)
{
world.setBlock(i , j , k, ModBase.nexussoil.blockID);
}
return true;
}
If not, then just tweak the code by changing the instanceof or adding !world.isRemote
If not, well, I don't know
EDIT:
Replace (equipped instanceof Wand1) with (equipped.itemId() == youritem.id)