Indicators of soil fertility and opportunities for precontact agriculture in Kona, Hawai'i

The distribution, mode, and intensity of agriculture both influence and are influenced by the natural environment. Soil fertility indicators that correlate with the intensification of dryland agriculture in pre-contact Hawai'i have been mapped across the Hawaiian archipelago. We investigated these soil fertility indicators and agricultural development in the unique environment of Kona, Hawai'i, the largest, culturally most significant, and geologically youngest of the dryland field systems in Hawai'i. Agriculture was intensified systematically on substrates >= 4,000 years old with appropriate climate and fertility in Kona, in keeping with archipelago-wide analyses. In comparison with other dryland agricultural systems in Hawaii, we found that soil fertility indicators used to predict pre-European agricultural intensification are shifted towards lower rainfall on the younger geological substrates of Kona. For example, base saturation reached low levels (<30%) at similar to 1200 mm/yr rainfall on 1,200 year old substrate and at similar to 1400 mm/yr on 7,500 year old substrate in Kona, versus similar to 1800 mm/yr on 150,000 year old substrate on Kohala Volcano. We suggest that this difference reflects a kinetic, rather than an irreversible, limitation to soil fertility in Kona, and we discuss how this difference could have influenced opportunities for agricultural intensification and the distribution of agroecological zones.