Soil nutrient analysis of Rapa Nui gardening

Abstract

Prehistoric Rapa Nui farmers used a variety of rock veneer and mulch gardens to increase crop productivity. These cultural features ranged from small ca. 10 x 10 m gardens, to much larger expanses of continuous rock concentrations covering many hectares. The rock gardens probably served several purposes, including protecting crops and soils from high winds, promoting water penetration, maintaining ground moisture, and reducing temperature fluctuations. In addition, soil nutrient dynamics might have been a factor in the construction of rock gardens. Analysis of soil nutrients within and outside of gardens suggests rainfall leaching significantly altered soil nutrients throughout the island. Furthermore, rock gardens generally have elevated levels of nutrients in relation to non-garden settings. This could have been the result of rock gardens functioning as the physical foci for increased organic mulching, the construction of gardens in natural nutrient rich sweet spots, or the elevation of nutrient levels within gardens via the weathering of relatively soft basaltic rocks. The research presented here documents the elevated soil nutrient levels of gardens and begins to investigate the reasons for this and the impacts it might have had on crop productivity.