Adam Clarke on Genesis 26:12

Isaac sowed in that land - Being now perfectly free from the fear of evil, he betakes himself to agricultural and pastoral pursuits, in which he has the especial blessing of God, so that his property becomes greatly increased.

A hundred-fold - מאה שערים, meah shearim, literally, "A hundred-fold of barley;" and so the Septuagint, ἑκατοστευουσαν κριθην. Perhaps such a crop of this grain was a rare occurrence in Gerar. The words, however, may be taken in a general way, as signifying a very great increase; so they are used by our Lord in the parable of the sower.