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Cambodian Researchers Use Isotopic Technique to Help Farmers Increase Yields and Revenues

Farmer Borey Thai has seen her rice yields increase by 20% as a result of using more manure and less inorganic fertilizer. She has also saved a third of the money she used to spend on fertilizer. (Photo: M. Gaspar/IAEA)

Phnom Penh, Cambodia – Poorer farmers who cannot afford to buy enough fertilizer can achieve high yields by using more manure and compost and planting alternative crops between rice growing seasons, Cambodia’s agricultural researchers have found. Their recommendations are the result of research supported by the IAEA and the Food and Agriculture Organization of the United Nations (FAO), using nuclear-related techniques to measure fertilizer and water uptake by rice and other crops.

Cambodia is among a growing number of countries using such techniques to increase crop yields, optimize fertilizer use and evaluate varieties of rice, cereals and vegetables for their efficiency in making the best use of fertilizers. (See Labelled nitrogen isotope for more) Currently, scientists from over 60 countries are benefiting from assistance in this area.

Blending organic and inorganic

Experiments conducted by scientists at the Cambodia Agricultural Research and Development Institute (CARDI) found that replacing half of the recommended amount of chemical fertilizer with organic materials when inorganic fertilizer is either not accessible or too expensive increases rice yields. This has various benefits, explained Sarith Hin, Head of Soil and Water Science at CARDI: farmers save money on chemical fertilizer, and at the same time they can achieve higher yields.

“The results demonstrate that even poorer farmers, who cannot afford to buy much fertilizer, can increase yields,” Hin said. In the case of peanuts, a legume cash crop, replacing half of the chemical fertilizers with a mix of cattle manure and rice straw more than doubled yields (see graph). For rice, the use of a reduced amount of chemical fertilizer with organic manure led to yields comparable to the use of chemical fertilizers only.

Agriculture accounts for 27% of Cambodia’s economy, and provides the livelihood of 60% of the population. Many of the country’s poor are subsistence farmers working on small plots of land, so increasing the productivity of their land is key to achieving higher income and escaping poverty. Historically, fertilizer use in Cambodia is neglected by farmers.  

Borey Thai, a farmer with 1.5 hectares of land in Kampong Speu province south of Phnom Penh, replaced half of the chemical fertilizer with a mix of manure and farmyard waste in this year’s growing season – and has saved a third of the money she used to spend on fertilizer. “It is much cheaper, but is more work,” she said. “But what matters is that I can use the savings to renovate my house.” She expects her yield to be around 20% higher this year compared to the previous year, thanks to the use of mixed fertilizer.

One challenge her neighbours face, she added, is to find good quality manure. “If we could find more manure, more of us would switch to organic.”

Alternative crops

Using the fields for the production of other crops in between rice growing seasons is another way for farmers to increase their income, found researchers of the country’s Ministry of Agriculture. Historically, farmers have used their fields only during the rainy season, when there is enough rain water to grow rice. During the dry season, lands are left idle.

Researchers have found that conditions during the dry season are optimal for other crops, particularly legumes such as beans and lentils. “These would not only provide farmers with additional income, but legumes add nitrogen from the atmosphere to the soil and, in addition, decomposing bean plants also increase the quality of the soil, leading to higher rice yields in the following rice season,” said Phirum. They used the nitrogen-15 isotopic technique to study the amount of fertilizer absorbed by the plants from the soil, fixed from the atmosphere, in addition to quantifying the efficiency of fertilizer applied.

The research teams received various forms of support under the IAEA’s technical cooperation programme. They learned the use of nuclear-related and other techniques in workshops and through participation in fellowships in neighbouring countries. They received equipment and materials to conduct the experiments, and advice from experts at the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture in interpreting the results.

A researcher experimenting with rice, using stable nitrogen-15 (15N) to monitor the nitrogen uptake by the plants. (Photo: Cambodia Agricultural Research and Development Institute (CARDI))

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