Nutrient and sediment retention in Andean raised-field agriculture

Abstract

RAISED-FIELD agriculture was widespread throughout Central and South America in prehispanic times^1,2. In this system of agriculture, crops are cultivated on a series of raised beds, which are separated from one another by deep, water-filled channels. In some regions, rehabilitation of the raised fields is now underway, largely because this practice leads to fertile soils, adequate water supply and protection from frost and therefore to substantially higher yields than more conventional methods^3,4. Here we report analyses of water quality in the channels alongside rehabilitated raised fields in the vicinity of Tiwanaku, on the Bolivian side of the Lake Titicaca basin (Fig. 1). We find that high concentrations of nitrate, available phosphate and turbidity decline significantly as the water flows through the raised-field channels. Water flowing through control sites shows no significant change.Retention of nutrients and suspended sediments in the channels helps to maintain soil fertility and reduces pollution of downstream waters. Thus it seems there are environmental benefits in rehabilitating raised fields, which complement and help sustain the economic benefits demonstrated previously^3,4.