No, I didn't post but will do now. Thanks for letting me know. Can you please suggest if there are more forums to get stat models' help especially MIXED model and repeated measures and for Analysis of Covariance.
One guesses that the syntax you attempted maybe should have read:
IF CROP = 'corn' THEN DELETE; /* must match the spelling and case of the value */
unless you intended to check if the value of the variable CROP was the same as the variable CORN.
Unless you really want to proliferate data sets, specifying a WHERE statement such as:
DATA=SOILS (where=(crop='corn')) in the proc call,
will accomplish the subset for any procs that do not directly support a where statement