Abstract
Data are presented on nutrient uptake of taro [Colocasia esculenta (L.) Schott] roots in relation to corm yield and above-ground biomass on a Typic Tropofluvents in the humid lowlands of Papua New Guinea. Fertilized (100:50:100 kg NPK ha-1) and unfertilized plants (n = 4 each) were harvested 126 days after planting (DAP) (mid-season) and 231 DAP (harvest). Rooting depth at both sampling times was <0.2 m and a unit soil area equivalent to the planting distance (0.5 m x 0.8 m) was removed from the field whereafter roots were washed on a 0.5-mm sieve. Root biomass at 126 DAP was 0.26 Mg ha- 1 (15% of total biomass) in the unfertilized plots and 0.52 Mg ha- 1 (13% of total) in the fertilized plots, but at 231 DAP root biomass was similar (0.50 Mg ha- 1). Root nutrient concentration at 126 DAP was similar in both plots but N, Ca, and S significantly declined in the unfertilized plots at 231 DAP whereas B increased with 18 mg kg-1 (P < 0.01). In the fertilized plot, P, K, Mg, Mn, and Cu had decreased at 231 DAP whereas Zn had significantly (P < 0.01) increased. Nutrients in the root biomass as a fraction of the total nutrient uptake were similar at 126 DAP for both treatments. At 231 DAP, however, the fraction of nutrients in the root biomass was considerably lower in the fertilized plots. There was a high uptake of Mg by taro roots in the unfertilized plots at 126 DAP (38% of total) and at 231 DAP (36% of total). This study has shown that the amount of nutrients taken up by roots of fertilized and unfertilized taro was similar at harvest, but that a much larger proportion of plant nutrients is allocated to the roots under unfertilized conditions.
