A cereal crop (4)
I believe the answer is:
oats
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">a cereal crop</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for oats that I've seen before include "Porridge ingredients" , "A cereal crop" , "Basis of porridge" , "Porridge ingredient" , "Grains or porridge" .)