org-agenda-add-entry-text-maxlines

org-agenda-add-entry-text-maxlines is a variable defined in `org-agenda.el'.
Its value is

0

Documentation:
Maximum number of entry text lines to be added to agenda.
This is only relevant when `org-agenda-add-entry-text' is part of
`org-agenda-before-write-hook', which is the default.
When this is 0, nothing will happen. When it is greater than 0, it
specifies the maximum number of lines that will be added for each entry
that is listed in the agenda view.

Note that this variable is not used during display, only when exporting
the agenda. For agenda display, see the variables `org-agenda-entry-text-mode'
and `org-agenda-entry-text-maxlines'.

You can customize this variable.