Date released
31 July 2018

Small landholder farmers in areas of the PNG highlands are facing declining soil fertility due to poor nutrient management practices and increased crop production pressures, a recent study has found.

The discovery was made by soil scientist Emma Kiup, who after recently completing her Masters studies at James Cook University, spent two six-week periods living in the Eastern Highlands Province village of Sogomi, Bena, located about 10 kilometres from the region’s main urban centre of Goroka.

The research conducted by Emma, which involved daily observations of the farming behaviours of six families and sampling their gardens for soil and harvested crops, was part of a ACIAR-funded project aiming to improving livelihoods of smallholder families through increased productivity of coffee-based farming systems.

The study found that soil nutrients were depleting due to the nutrient requirements of crops and poor nutrient management practices, including the low input system practised by the smallholders. Emma’s study identified how adopting nutrient retention practices, such as retaining crop residues or waste to maintain soil fertility, could benefit the farming system.

‘The soil in Bena is generally fertile for crop production but some of the soil nutrients are depleting due to the nutrient requirements of the local crops and poor nutrient management practices,' says Emma.

‘The low input system practised by the smallholders exacerbates the nutrient decline because the use of commercial fertilisers is minimal and is limited to farmers who cultivate commercial crops that are perceived to be nutrient demanding such as cabbage, broccoli and cauliflower.

'However, even for the fertilized crops, the fertiliser application rate is quite low compared with the substantial amount of nutrients exported by the crops.'

Emma also found that although coffee is the main cash crop for farmers in the highlands of PNG, because of its seasonality and fluctuating prices, farmers have diversified into the production the annual production of other crops to maintain cash flow throughout the year.

Farmers' ability to access the urban market is one of the driving factors in their diversification of crop production, meeting food demands of the increasing urban population. The demand also affects the intensity of crops grown for selling at market.

Traditional farming of subsistence foods involved long fallow periods between crop rotations to allow the soil to rejuvenate; but market demand is resulting in multiple crops per year in the same garden bed with short or no fallow periods. 

The process of crop harvesting and preparation results in the production of residues or wastes that could be better managed to retain soil nutrients. The study showed that the application of crop residue/waste to certain parts of the garden improved the physical and chemical properties of the soil, especially the potassium content.

However, these wastes are often not utilised effectively. For example coffee pulp (produced when processing coffee cherry to parchment coffee) is very high in nitrogen and potassium (important plant nutrients) but is often left to decompose at the pulping station.

The option of retaining crop residues or waste is beneficial for the farming system but may be perceived as inconvenient and not practiced because the value of the nutrients in the waste is not appreciated. For example, the crown of a pineapple is a convenient ‘handle’ to transport the pineapple to market, where it is removed. However, a substantial amount of nitrogen and potassium are present in the crown, which could have returned nutrients to the garden if processed on site.Therefore, adoption of nutrient retention practices will require education about the value of nutrients in waste products versus the value of convenience.

The farmer can increase the fertiliser application rate as the amount of fertiliser applied per plant is quite low and the money spent on purchasing fertiliser to replace nutrients removed from the crop during harvesting can be recouped when the crop is sold in the market.

One of the important lessons learnt during the fieldwork was that there is no ‘standard’ practice—each farmer’s practice varies, even between neighbours growing the same crop. The difference in approaches to farming practices can be attributed to experience, or lack of it. That means, changing the attitude of farmers towards adopting new ideas and farming practices may take a long while. 


While carrying out this important research in the highlands of PNG, Emma faced the challenging road of obtaining a Master's degree, a journey especially difficult for an early-career scientist with a young family who had never travelled overseas before.

'I would not have thought I had the strength to overcome the constant pressures that came with balancing my studies and looking after my family on my own, while living in a new community here in Australia,' says Emma.

But with financial support from ACIAR through the John Allwright Fellowship, and further assistance from CSIRO, Curtin University and the PNG Coffee Industry Corporation, Emma completed her post-graduate studies at James Cook University. This assistance enabled Emma to further develop her career and take her newfound knowledge back home, enhancing the research capacity of PNG in the process.

As well as overcoming personal challenges to complete her masters, Emma also faced hurdles conducting the research.

'Apart from the country’s challenging geography, working with the people from different communities with differing levels of understanding of my work and agricultural science research is also very challenging,' says Emma. 'A detailed discussion with the farmers at the beginning was important to reduce any problems that might arise during the course of the project.'

Emma completed her thesis in 2017 and is currently working on another ACIAR-funded project through Curtin University, Improving Livelihoods of Smallholder Coffee Communities in PNG, and hopes that inter-cropping vegetables in coffee garden will lead to improved soil fertility, coffee quality and increase farmer income.

The project is supported by the CSIRO and the PNG Coffee Industry Corporation and is due to run until the end of 2021.