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Date released
07 March 2025

In the heart of South-East Asia, Cambodia’s agricultural landscape has undergone a transformation as the country’s upland regions are further populated and developed.

A recent ACIAR-supported project focused on better understanding and identifying the region’s soils. It has shed light on the benefits of more sustainable practices for smallholder farmers who rely on cropping for their livelihoods and food security. It has also helped to build the capacity of local researchers and government officials.

Leader of the Cambodian Upland Soils Project (CUSP) Dr Wendy Vance, from Murdoch University in Perth, said the project built on a previous ACIAR-supported project from 2003 to 2007 that surveyed soils and completed land suitability assessment in 5 upland districts.

Soil maps for new farming region

Dr Vance said the soils of the lowland regions, which have been used for rice production for thousands of years, had been well described and mapped for their suitability for growing rice and other crops.

By contrast, development of the upland region for agriculture has mostly occurred in the past 20 years – often by newcomers to the area – encouraged by government economic and social land concessions. Social land concessions have allowed people to build a home and engage in subsistence farming. 

Smallholder farmers occupy about 27% of the uplands’ 3 million hectares. They typically operate traditional farming systems with limited knowledge of soil constraints and crop management technologies, and are especially vulnerable to crop failure and land degradation. 

Dr Vance said this had, in many cases, resulted in continuous cropping and declining yields caused by soil nutrient decline and losses via erosion.

The CUSP aimed to address knowledge and yield gaps by introducing new methods for soil and land suitability assessment, identifying soil types and landscape patterns, and characterising soil constraints. 

‘We also wanted to provide tools and information for the stakeholders,’ said Dr Vance. ‘That could mean farmers, but it could [also] mean researchers and students so that they could identify main soil types and their constraints to crop production.’

Two people inspected vegetable leaves
Dr Sarith Hin (Deputy Director, CARDI) (left) and farmer Ek Mon check the leaves of cucumber plants for signs of nutrient deficiency.

Local knowledge

The project’s key achievements included combining scientific expertise with local knowledge, and training research and extension staff of project partners (the Cambodian Agricultural Research and Development Institute and the Royal University of Agriculture in Cambodia). Strong collaborative engagement and support from these organisations were essential to the success of the project.

Combining traditional soil survey techniques with new laboratory rapid soil analysis techniques, such as mid-infrared spectroscopy, the project team identified 4 new soil types specific to upland areas. Detailed soil landscape maps were produced for the 2 districts they studied.

The researchers found smallholder farmers in 3 villages were able to describe their soils, differentiate between soil types from the local area and explain how they affected crop yields.

Through community activities, the research team engaged farmers in discussions to validate their existing knowledge and to help farmers learn how to correctly identify when crop symptoms were caused by nutrient deficiency rather than water stress, pests or disease.

On-farm trials and field days involving more than 300 farmers also demonstrated the benefits of proper fertiliser use, particularly nitrogen, phosphorus, potassium and gypsum, and adding lime to manage low pH.

We were able to show these farmers that fertiliser use improves plant growth and yield.

Dr Wendy Vance
Project Leader, Murdoch Univeristy

‘And they could consider what the economic benefits could be, as well as what the risks could be to them if they were to add fertiliser [at the] recommended rate or double recommended rate.’

The trials were simple but clearly showed the positive impact of adding organic or inorganic fertiliser to nutrient-deficient soils.

Peanut yields increased by up to 47% in the early wet season and profits rose 60%. In the main wet season, yields rose 25% and profits were 30% higher.

Dr Vance said many of the farmers in the program, which operated from 2018 to 2022, have continued to use fertiliser, often applying it more precisely to individual plants during important stages of plant growth.

Benefits for smallholder farmers

The demonstrations have already made a difference for smallholder farmers in the Aoral district of Kampong Speu province, west of Phnom Penh. 

These include Mr Oum Samun, who said he had seen significant improvements in his peanut crops after putting into practice training on how and when to apply fertilisers, and which to apply.

Mr Samun said his crops had suffered shell damage, but fertiliser helped the roots grow stronger and healthier, and boosted the number of harvestable pods per plant.

‘The project team suggested that I could apply these effective fertilisation techniques to other types of legumes, potentially enhancing their growth and yield as well,’ said Mr Samun.

Farmer Oum Samun showcases a healthy peanut plant.
Farmer Oum Samun showcases a healthy peanut plant. Fertiliser use has helped boost root growth and plant health, and reduce pod rot, increasing yields.

Mrs Ek Mon and her husband moved to Reaksmei Sameakki commune to take up a social land concession a decade ago. At the time their plot was surrounded by forest, but much of it has now been cleared because of a surge in population and demand for land and resources.

At the same time, soil fertility and yields have declined, prompting Mrs Mon to take part in ACIAR-supported projects focused on sustainability and restoring soil health. She was keen to learn how to improve her peanut crops.

Mrs Mon has since translated the techniques learned from the CUSP trials to growing cucumbers. But despite high demand for cucumbers this season, she has been reluctant to invest in all the recommended fertilisers because of the cost.

‘The market price [of cucumbers] keeps fluctuating. I am concerned that I won’t be able to make enough profit from selling cucumbers to pay for those chemical fertilisers. However, I have decided to use a combination of both chemical and organic fertilisers from manure,’ said Mrs Mon.

Similar projects to survey soils and upskill local scientists in the use of rapid soil analysis tools are underway in the Pacific islands of Samoa, Tonga, Vanuatu and Fiji, and in Papua New Guinea. These projects use techniques developed in previous ACIAR-supported projects in the Philippines and Myanmar.

ACIAR Project: 'Land suitability assessment and site-specific soil management for Cambodian uplands’ (SMCN/2016/237)