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.