First tab, don't be too harsh :)
First Riff:
e|------------------------------------------|
B|------------------------------------------|
G|------------------------------------------|
D|------------------------------------------|
A|-------------22-4-2--5-2-4-5-4-2----------|
E|-2(b)--00-44---------------------4--0-----|
Second Riff:
[ Tab from: http://www.guitaretab.com/j/johnny-cash/159660.html ]
Move entire frame up 1 string, repeat
Third Riff:
e|--------------------------------------------------------|
B|--------------------------------------------------------|
G|--------------------------------------------------------|
D|-------44-6-4--7-4-6-7-6-4----------22---22-------2---2-|
A|-22-66---------------------6-2--------42---42------42---|
E|--------------------------------------------------------|