Soil Nutrients and Traditional Agriculture on Young Volcanic Soils on Ta’ū, American Samoa

Abstract

Soils and agriculture are inextricably linked, in the past as well as today. How and where people developed agriculture based on soil and landscape properties has not been well developed in the Pacific. Pacific Islands, which often represent nicely organized gradients of substrate age, rainfall, and soil type, represent excellent study systems to understand this interaction between people and soils. Agriculture in Polynesia has been mostly subsistence, in the past and, in many islands, still today. While some agricultural forms have received intensive study, others still lack information and knowledge, particularly those that experienced abandonment following European contact. This is the case of extensive rainfed agricultural systems in the Manu’a islands of American Samoa. To understand prehistoric agricultural systems, we sampled along transects that crossed through intensive agriculture infrastructure in the upland of Fiti’uta on Ta’ū island. Soils were analyzed for several soil fertility properties that have been proposed as indicators of Polynesian agricultural intensification in related systems seen in Hawaii and Rapa Nui. Surveys of remnant economic plants were conducted along the same transects. Data suggest that the previously identified soil fertility indicators aligned well with the agricultural infrastructure on Ta’ū except for exchangeable calcium, which was significantly more depleted than other intensified agriculture in the Pacific. The soil fertility results also correlated well with the vegetation agricultural survey, specifically with the younger Ta’ū soils.