The country of Ilina has always been desperately poor, but a recent increase in the affordability of growth-enhancing chemical fertilizers has made their use commonplace among struggling Ilinan farmers, which has in turn boosted crop yields significantly. As a result, the Ilinan production of food grains has tripled in the last three years; however, the country's production of vegetables has decreased by half over the same period.
Which of the following, if true, provides the best explanation of the contrast described above between production of food grains and production of vegetables?