Production issues of sweet potato needs addressing

By JOSEPHINE YAGA of NARI
The adoption of interventions or introduced innovative agricultural practices is being absorbed in a rapid pace as demand for food and cash crops increases.
Hence continuous use of arable land leaves less or no time for fallow periods to replenish soil fertility and this is leading to land degradation
Amongst the foods cultivated, sweet potato accounts for 63% of the dietary energy of the population and is becoming the mainstay of the country's food security.

Participants Singis Ketti (left) and Dulcie Fonny gathering sweet potatoes after harvest.  Behind them are groups of sweet potatoes piled on the mounds where they were dug

Current production is more than three million tones per annum and is worth an estimated $A700 million.
Not withstanding the dominance of the crop, both to the subsistence economy and increasingly as a cash crop on domestic markets, the crop has been facing production problems.
Apart from climatic factors such as El Nino events, which causes major but temporary fall in production, farmers and scientists, have noted a gradual decline in yields and the quality of tubers, the cause of which is not always obvious.
This decline has implications on food security.
A number of pests and diseases, along with crop physiology issues have been identified which may be involved in the decline.
Main research issues in PNG include the causes of apparent yield decline over time for some cultivars, the influence of soil moisture extremes on crop growth and yield and of soil moisture by nitrogen interactions, management of cultivars by villagers including cultivar replacement and soil fertility management.
Due to its importance in PNG, sweet potato features prominently in the National Agricultural Research Institute’s (NARI) strategic plan.
There are currently five research projects being undertaken by NARI.
The projects are based on on-farm variety testing and dissemination, crop improvement through cleaning of planting materials (in tissue culture), management of major pest and diseases and management of soil / water for improved productivity.
Improved marketing opportunities through improved post harvest management and product development remains the priority now for NARI, to maximise benefits to farmers.
Farmer awareness and training on best management practices and availability of improved clean and improved drought tolerant sweet potato varieties have been conducted in the highlands and the lowlands to help farmers identify quality planting materials and address areas resulting to low yield.
One of such training ended last week in which participants, mostly women from 12-Mile, Huon Gulf district in Morobe province, received certificates of achievement after completing three months (theory and practical) of training under a project titled “the use of pathogen tested planting materials to improve sustainable sweet potato production in Papua New Guinea and Solomon Islands”.

Participants of the sweet potato training (women dressed in red) displaying their certificates of achievement. The certificates were presented by  NARI information and knowledge programme director Dr Pikah Kohun (left)  and senior agronomist Elick Guaf

The project is funded by the Australian Centre for International Agricultural Research (ACIAR), Australia, and the Centre for International Potato, Peru.
The objective of the training was to promote the sustainability of sweet potato production and post-harvest management through best practices in the sweet potato production by starting with using clean planting materials for good yield.
Virus and disease free sweet potato or pathogen-tested vines were collected from screen houses at the NARI Momase regional centre, Bubia, and distributed during the practical sessions.
The plants were planted and over three months with good management practices including good size mounds, drainage, cuttings per mound, spacing of plants, timely weeding, hilling up and timely harvest were thought and practiced.
No fertiliser or animal manure was used in this training to improve yield.
“Selection and distribution of clean materials is very important and we are also planning to train farmers on best practices in the production of other staple crops under the NARI information and knowledge programme,” said Elick Guaf, NARI’s senior agronomist.
Sweet potatoes grown in the lowlands take more then four months to mature but planting early maturing clean materials and using best management and production practices promote crops to mature in only three months with quality and increased yields.
NARI released 79 sweet potato varieties suitable for the lowland conditions of PNG.
These included four lowlands drought tolerant varieties previously released by NARI as a drought-coping strategy.
All these cultivars have acceptable yields with good market and consumer appeal.
They also have a range of other positive traits such as good tuber shape and colour (including orange tuber flesh colour with a high beta-carotene content), high dry matter content, good processing characteristics, firm flesh texture after boiling and preferred degree of sweetness which allow the growers and end users to choose the variety that best suits their needs or preferences.