The timing of the Lamanite attack appears to have been at the end of the growing season, when the crops were still in the field. Thus the armies trampling through the fields have destroyed the grain. We see the effects of this in Alma 4:2 where a the Nephites suffer from the loss of their flocks and herds and grain.
The analysis just above presented information that warfare was seasonal, and that the ability to provision troops was important to being able to continue warfare. In this case, however, we have a large invading Lamanite army at a time just before the harvest instead of after. Why does this attack appear to violate the timing Sorenson has proposed?
It is quite possible that it does not entirely go against the evidence Sorenson has presented. What it would require is that the Lamanites have provisions, but that the Nephite crops were still in the field. In the proposed location for Book of Mormon events, Zarahemla would be at a higher altitude, and probably a slightly cooler climate that the invading Lamanites. This difference in altitude and temperature could create a slight difference in the growing seasons between the lands of the Lamanites and the Nephites. The Lamanites could have been home to gather in the crops, and then left immediately to strike against the Nephites. The differential in time would find the Nephite crops still in the field.
It is also quite probable that the Lamanites did not expect a prolonged action. If Sorenson is correct that the Amlicites were in collusion with the Lamanites, then there would be an expectation of a quick victory, and therefore a lesser need for carried provisions. Rather than bringing a lot of food with them, the Lamanites would have expected to eat from the captured bounty of the Nephites.