In this project, P-dipping, a fertilization technique^*1 that can significantly improve the productivity of paddy rice farming with a small amount of a fertilizer, was developed through international cooperation between Japan and Madagascar, and the significant effect of this technique was successfully demonstrated in more than 3,000 farmers' farm fields in Madagascar. This technique is a simple method of adhering mud mixed with a phosphorus fertilizer to the roots of rice seedlings at trasnplanting. It is highly regarded as a method that can be used easily by poor farmers in Madagascar, where the use of chemical fertilizers and other agricultural materials and equipment is restricted, and its widespread use in the country is being promoted.

It was also demonstrated that P-dipping not only can increase rice production with a small amount of fertilizer but is also effective in avoiding poor grain filling^*2 and flood damage^*3. Therefore, these results are expected to widely contribute to improving rice farming not only in Madagascar but also in Sub-Saharan Africa,^*4 which is exposed to international skyrocketing fertilizer prices and various kinds of severe environmental stresses with the climate change.

The research team consists mainly of young researchers from various fields in Japan and Madagascar, and the project also contributes to effectively developing human resources (Fig.1). The Minister of Agriculture and Livestock of Madagascar presented a certificate of appreciation for these achievements.

*1 Fertilization technique
The method of fertilizing must be optimized according to the conditions in which the farmland is located. A fertilization technique is a comprehensive technique that requires knowledge of soil fertilizers and crop cultivation as well as knowledge of weather and management.

*2 Poor grain filling
A phenomenon in which poor rice ripening is caused by exposure to low temperature or other kinds of stress during the flowering period or grain filling period and results in an increase in sterile spikelets and a lower yield.

*3 Flood damage
A phenomenon in which an increase in the paddy field water level after transplanting causes most or all of the rice plants to be inundated with water, which prevents its respiration and photosynthesis and inhibits its growth or causes it to wither.

*4 Sub-Saharan Africa
The Sahara Desert and the area to its south. This area has low farming productivity and is suffering from the most serious poverty and starvation in the world.

International skyrocketing fertilizer prices are a common issue for Sub-Saharan African countries including Madagascar. Since farmers there are poor and have little purchasing power, they cannot afford to use adequate amounts of fertilizers. Also, influenced by the Russian invasion of Ukraine, the situation has been further deteriorating. The World Bank has reported that while chemical fertilizer consumption decreased by 5% worldwide in 2022, it might have decreased by up to 25% in Sub-Saharan Africa.

In addition, more than half of the paddy fields in Sub-Saharan Africa do not have adequate irrigation and drainage facilities and rely on rainwater or the like for water necessary for cultivation. Inherently, the paddy fields there are susceptible to water shortages and flooding and the production has been unstable due to the frequent occurrences of drought and heavy rains caused by climate change. The number of floods in Africa has doubled in the past 30 years, and the heavy rains in southeastern Africa between 2019 and 2020 caused significant damage to agricultural production in the area.

The rice consumption per capita in Madagascar is more than twice that of Japan, and more than half the country's population is engaged in rice cropping. However, their rice yield per hectare is less than half that of Japan, which, in combination with the aforementioned conditions, has caused them to face serious poverty and starvation. There is a need to develop a production technique that can efficiently improve crop productivity with a small amount of fertilizer and is resilient to climate change.

Inspired by Japan's rice cropping technique in the Meiji period, the research group led by the project leader Yasuhiro Tsujimoto developed phosphorus dipping or P-dipping, which is a fertilization technique of adhering mud mixed with a small amount of phosphorus fertilizer to rice roots before transplanting. The research group previously demonstrated that P-dipping can improve rice production in phosphorus deficit paddy fields commonly seen in Madagascar and help to avoid cold weather damage caused by temperature reductions in the latter half of the growing season by shortening the growing period (Fig.2).

This research project focused on elucidating the technique's previously unidentified effects. By applying P-dipping in paddy fields susceptible to various kinds of environmental stress caused by water shortages, flooding, and other weather factors, the extent to which this technique would be effective to increase rice yields was elucidated. By applying the technique in 18 test paddy fields with different weather and terrain conditions and changing cultivation conditions such as dates of transplanting and nitrogen fertilization, the standard effects of P-dipping and in what cultivation environment the technique would work were more effectively clarified.

① Effects on rice yields and fertilizer efficiency

The average per hectare rice yield of the test farm fields increased by 1.1 tons compared to that with no phosphorus fertilizer. It increased by 0.5 tons compared to the case when the same amount of a phosphorus fertilizer was applied via broadcast as is conventionally done. When used in combination with nitrogen fertilization, the difference in rice yield was increased and the efficiency of nitrogen use was improved (Fig.3).

③ Effect of avoiding low temperature stress

It was confirmed that reducing the number of days from transplanting to harvesting helps avoid low temperature stress caused by temperature reductions in the latter half of the growing season and improve the grain fertility^*5, as is conventionally known. It was found that P-dipping was quite effective in increasing the rice yield not only in cool areas at high altitudes but also in warm areas when the date of transplanting was late (Fig.5).

*5 grain fertility
Numerical value calculated by multiplying the percentage of filled grains (ratio of the number of filled spikelets to the total number of spikelets) by the filled grain weight (g). The grain fertility decreases as sterile or immature grains increase due to low temperature stress.

In addition, the research group was convinced of the effectiveness of the technique from repeated verification in farm fields and provided technical training on P-dipping for more than 3,000 local farmers together with the regional extension offices of the Ministry of Agriculture and Livestock of Madagascar. As a result, many farmers adopted the P-dipping technique and it increased the average per hectare rice yield by approximately 1.1 tons (30%) from 3.7 tons to 4.8 tons. In response to the dissemination of the technique among farmers, private companies in Madagascar started selling fertilizers for P-dipping, and the Japan International Cooperation Agency (JICA) is planning to launch a social implementation type technical cooperation project with the aim of promoting the wider dissemination of the technique in other areas in fiscal 2024. Therefore, movements toward applying the research results in society have been accelerating (Fig.6 and 7).

Increasing rice production in Africa is an urgent issue to be addressed to respond to the ever-increasing demand. The results of this research indicate that the value of using fertilizer might be increased by adopting P-dipping and that doing so might also help cope with the frequent occurrences of flood damage. These achievements can be highly regarded as making a significant contribution to improving rice cultivation not only in Madagascar but also in other regions under similar environmental conditions. The widespread use of this technique is expected to contribute to stable and sustainable rice production in Sub-Saharan Africa.