You are correct.  The weight of the water above the outlet determines the pressure of the water at the outlet, when the water is not moving in the pipes. 

In the illustration below a volume of water is shown (1 cubic foot).  

A one square inch column of water from the corner of the cube is shaded (see image above).  It is 12 inches tall and one square inch in area (see image below).  The pressure at the base of this column is .433  pounds per square inch (PSI ).  Each foot added to the column height would add an additional .433 PSI to the pressure at the base of the column. 

Note that this is static pressure, that is pressure exerted by water at rest.  So we can say that the static pressure at any point in the irrigation system can be determined by the difference in elevation between the source of the water and the outlet point multiplied by .433