Unburnt bush fallows — a preliminary investigation of soil conditions in a bush fallow and two successive crops of taro (Colocasia esculenta (L.) Schott) in Western Samoa

Abstract

Abstract Little research has examined shifting cultivation systems that do not burn their bush fallows. This work examines three phases of shifting cultivation (mature bush fallow and the first and second successive taro crops) on five inceptisols (Falealili, Tiavi, Etimuli, A'ana and Avele) in Western Samoa during May 1990. Traditional farming practice was used on all sites, including not burning the bush fallows after they were cut down. The soil bulk density increased with the phases of shifting cultivation on the Falealili soil. The soil water content at both field capacity and wilting point and the available water capacity increased with the incorporation of the bush fallow, and then decreased with cropping. The flush of nutrients following the bush fallow was small, and included increases in potassium on the Tiavi soil, calcium on the Etimuli and A'ana soils, magnesium and total exchangeable base content on the Tiavi and Etimuli soils, manganese on the Avele soil and zinc on the Etimuli soil. There were also decreases in soil phosphorus on the Tiavi and Avele soils. Changes in taro nutrient concentration with cropping included decreases in foliar nitrogen on the Falealili soil and sodium on the A'ana soil, and increases in foliar magnesium on the Etimuli and A'ana soils. More long-term research is needed on shifting cultivation systems that do not burn their bush fallows.