Better nutrition for the improvement of sweetpotato and taro yields in theSouth Pacific

Poor crop nutrition contributes to the low yields of root crops in the Sout h Pacific region where symptoms of nutritional disorders are frequently obs erved. This study was therefore undertaken to assess the effect of inorgani c fertilizers on sweetpotato [Ipomoea batatas (L.)] and tare [Colocasia esc ulenta (L.) Schott] yields. It indicates the importance of the correct diag nosis of the nutritional problems at each site for improved nutrition manag ement and describes procedures used to identify and correct nutritional lim itations to growth. Nutrient deficiencies were detected using nutrient omis sion pot trials and the amounts of fertilizer nutrients required to correct deficiencies were determined in a series of Dot and field trials. Placemen t of P fertilizers and number and timing of N applications were found to in crease fertilizer efficiencies. Critical leaf concentrations of N and P wer e determined. Leaf concentrations sampled during early vegetative growth we re found to be good indicators of the effect of N or P deficiency on yield. Economic analysis of fertilizer applications demonstrated a high level of profitability.