No abstract

Large mounds amended with plant residues are a common cultivation method for sweetpotato (Ipomoea batatas) in the western parts of the Papua New Guinea highlands, with a suggested benefit of elevated root zone temperature (RZT) from decomposition. This study aimed to evaluate whether RZT affects the formation and growth of sweetpotato storage roots. Experiments evaluated the effects of a constant elevated RZT on the Beauregard cultivar and of a short‐term increase in RZT on the Beauregard and Northern Star cultivars. Plants were grown in 18‐L pots divided into a control compartment (constant RZT at 20°C) and a treated compartment (RZT at 30, 40 or 50°C). Constant elevated RZT was maintained until harvest, while short‐term increase in RZT occurred in weeks 2 and 3 only. Constant elevated RZT did not affect the total number of storage roots, but RZT of 30°C and above reduced the dry‐biomass of storage roots. The short‐term increase in RZT did not alter the total number or dry‐biomass of storage roots in Beauregard, while both of these attributes were reduced at RZT of 40°C or above in Northern Star. Elevated RZT inhibited dry‐biomass accumulation of storage root, with a more pronounced impact at constant elevated RZT. These results demonstrate that any benefits of the mound culture on sweetpotato yield production do not arise through the influence of temperature elevation.

Sweetpotato (Ipomoea batatas) is an important food crop grown widely throughout the world. In Papua New Guinea (PNG), sweetpotato is a staple food, with more than two-thirds of total production occurring in the highlands region. Although mound cultivation is commonly used for sweetpotato production throughout PNG, a unique cultivation method is used in the Western highlands provinces whereby sweetpotato is grown on a large mound amended with plant residues. Decomposition of these residues releases nitrogen (N) and increases mound temperature, which is ix Contributions by others to the thesis This thesis is the original work of Prapa Taranet. Additional contributions were made by Dr.