This is related to the greater efficiency of farming, combined with the increased level of value addition (e.g. more highly processed products) provided by the supply chain.
ðɪs ɪz ɹᵻlˈeɪɾᵻd tə ðə ɡɹˈeɪɾɚɹ ɪfˈɪʃənsi ʌv fˈɑːɹmɪŋ, kəmbˈaɪnd wɪððɪ ɪŋkɹˈiːst lˈɛvəl ʌv vˈæljuː ɐdˈɪʃən ˈiː.dʒˈiː. mˈoːɹ hˈaɪli pɹˈɑːsɛst pɹˈɑːdʌkts pɹəvˈaɪdᵻd baɪ ðə səplˈaɪ tʃˈeɪn.