create DB trigger that will call a stored procedure

I found an example (that doesn't work...)
create trigger gemlib.iimtrgr1
after update of IDESC , IUMS, IUMP, IITYP
on gemlib.iim
REFERENCING NEW as n
FOR EACH ROW
BEGIN ATOMIC
CALL KSQLLIB.UPDIIMDTA1 (n.IPROD) ;
END

the above fails saying "variable IPROD not found or usable"...

however, If I do this:

create trigger gemlib.iimtrgr1
after update of IDESC , IUMS, IUMP, IITYP
on gemlib.iim
REFERENCING NEW as n
FOR EACH ROW
BEGIN ATOMIC
Declare iprod15 CHAR(15) ;
SET iprod15 = n.IPROD;
CALL KSQLLIB.UPDIIMDTA1 (iprod15) ;
END

that works....
But that seems like I am overdoing it....