A project undertaken at PNG National Agricultural Research Institute (NARI), and supervised by Mr William Sirabis
Sweetpotato (Ipomoea batatas (L) Lam) is a historical staple crop in the Papua New Guinea (PNG) Highlands and has gained economic significance over the years. In the 1980s, the Australian Government, through the Australian Center of International Agricultural Research (ACIAR), invested heavily in introducing Pathogen-tested (PT) sweetpotato. This initiative resulted in the establishment of pathogen-testing technology in 2005, enabling the production of virus-free planting material and promoting ten local sweetpotato cultivars suitable for commercial production in the PNG Highlands.
Cultivation of these elite sweetpotato materials has gained importance for income generation in a market-oriented economy. However, significant knowledge gaps exist in effectively utilizing the technology. Currently, there is insufficient information regarding specific soil nutrient management strategies for individual PT sweetpotato cultivars. Despite the notable increase in marketable storage root yields compared to field material, intensive production of these cultivars poses a risk of rapid soil nutrient depletion.
Nitrogen (N) is the primary limiting soil nutrient in tropical cropping systems. In the past decade, NARI ACIAR-funded projects aimed to support soil fertility in sweetpotato cropping systems in the PNG Highlands, with a growing focus on PT sweetpotato. However, research on synthetic fertilizer use, particularly regarding N, remains limited and inadequately documented.
This research project aims to assess N fertilizer responses in different PT sweetpotato cultivars, recognizing their unique N requirements. Also factors like geographic locations, climates, and cropping seasons can influence N response. The study will emphasize determining optimal application rates and timing, offering insights into enhancing N fertilizer use for PT technology.
The sweetpotato development cycle encompasses three phases within 90-150 days: establishment, storage root initiation, and root bulking. Timely N fertilization in the early stages is vital, as rapid storage root initiation requires N within the first week of planting. Alternatively, delayed N applications, 2 to 5 weeks after planting, have shown potential for high yields. Split treatments with reduced N amounts have also improved nutrient uptake and use efficiency.
Therefore, the research objectives comprise evaluating the effects of varying N application methods, encompassing rates and timing, on the growth and development of individual PT sweetpotato cultivars. Additionally, the study intends to identify any seasonal differences resulting from these N application methods. Ultimately, the scientific goal is to determine suitable N fertilizer methods for optimizing the growth and development of PT sweetpotato cultivars in highland agro-ecological zones of PNG. This research holds the potential to bridge critical knowledge gaps and contribute to sustainable sweetpotato production in the region. Furthermore, this research will set a benchmark for evaluating alternative nutrient sources and practices to enhance nutrient management effectively.