Legume cultivation by Ryukoku University’s Faculty of Agriculture in converted fields

Date of interview	September 22, 2021
Targets	Dr. Hiroyuki Daimon, Professor, Faculty of Agriculture, Ryukoku University

Please give us an overview of the Laboratory of Crop Science at Ryukoku University’s Faculty of Agriculture.

As the impact of climate change on agricultural products is becoming more severe each year, steady food supply is also becoming increasingly inaccessible. To address the situation, we have been conducting research with the objective of establishing a systematic and sustainable crop production method that has reduced negative effects on the environment and requires less fossil energy.
While arable land absorbs carbon dioxide in gas form and helps mitigate global warming, paddy fields have its disadvantage of methane gas emissions, and cropland emits nitrous oxide that is another type of greenhouse gases. As the country strives to achieve carbon neutrality by 2050, there might be a variety of pathways to meeting the goal, as described in the Strategy for Sustainable Food Systems, MeaDRI (measures for achievement of Decarbonization and Resilience with Innovation) published by Japan’s Ministry of Agriculture, Forestry and Fisheries, by increasing organic farming from the current ratio of less than 0.5% to about 25%, and reducing chemical fertilizer use to cut gas emissions, etc. As we collectively live in this society going through such transformation, I have been contemplating with my students what we might be able to do to make it better.
For example, our research has been focusing on the peanut among other legumes, which can substitute for, and help reduce the use of, chemical fertilizers if their stems and leaves that remain after nuts harvesting are plowed into the field as organic material. However, as they decompose underground, nitrous oxide is still produced. So I believe we need to compare all numerical data available to find an optimal balance between the different options.

Please tell us more about the Faculty of Agriculture’s ranch and farmland.

The piece of university property has been used for undergraduate students’ practicums as well as for graduate students’ research activities involving the cultivation of the adzuki bean (Vigna angularis), soybean, peanut, etc. Because of its proximity to Lake Biwa, we have been able to practice environmentally conscious agriculture, using only 50% of the amounts of fertilizers and other agricultural chemicals that are normally used. The farmland has an area of roughly 3 hectares, which used to be a paddy field. While we converted a half of the area into the field for practicums, this region has historically been famous for rice farming. As the temperature variation between day and night is quite significant in the region, it is optimal for growing delicious rice.
Behind the farmland, there is this large river called Daido Gawa, which used to flood quite often apparently. As the inundation brought the fertile soil downstream, the land is so robust, but as the paddy field that used to be here was converted into the farmland, the robustness of the soil has been waning over time. So we have been thinking about ways to put a stop to it.

What are the characteristics of the adzuki bean that is grown here?

How we grow the adzuki here is a little different from the cultivation method usually used in Hokkaido, which is the main producer of the legume in Japan. While the beans are harvested in Hokkaido in or around summer, the variety being cultivated here is known as aki-azuki (fall adzuki) that is harvested from late October through November. The specific cultivar’s name is dainagon-azuki, which is a large-grain adzuki that presents such an aesthetically-pleasing look when used in traditional Japanese confections. Therefore, the color of each grain must be good and their size large and even. As it does not take long for the cultivar to bloom after its seeds are sown, it is important that all adzuki plants get proper sunlight exposure for their normal photosynthesis in order to grow sufficient numbers of pods and large seeds inside them.

Please tell us what type of climate is suitable for legume cultivation.

Because their roots are inhabited by a special type of bacteria called rhizobia, legume plants do not require much nitrogen fertilization. However, many legumes are susceptible to damage caused by excess water. In the case of farmland converted from paddy fields such as ours, the ground tends to hold water, leading to poor germination and root rot. In other words, to avoid such issues, attention must be paid to the amount and timing of precipitation and their relation. So, when the rainy season arrives and passes each year does affect the timing of seed planting significantly. Since the rainy season has gotten longer in recent years, the harvest varies widely from one year to another. In the case of adzuki plants, if there is so much precipitation close to their blooming season to cause inundation, their pollination fails and no beans grow. While the soybean is more resilient against inundation to a degree, the adzuki bean is highly susceptible to too much water.
On the other hand, if adzuki plants do not get enough sunlight at the time of their pod growth, they are unable to photosynthesize properly, resulting in poor bean growth.

Please tell us what adaptation measures can be implemented to deal with increasing rainfalls caused by climate change, etc. as well as about your survey and research activities related to this point. Also tell us what activities are underway to prepare for the future, and any issues, etc. you may be experiencing.

As climate change has been in our social discourse in various forms, both farmers and consumers are aware of the issue. So researchers like us that are engaged in the development of plant cultivation techniques must come up with adaptation measures that are optimized for each crop and cultivar.
In this particular area, we plant adzuki seeds around July 15. However, as mid-July usually coincides with the end of the rainy season, many large fields become too soft and wet from the rain for the sowing tractors to enter. Even if sowing is done in early August to avoid the rainy season, the flowers bloom shortly thereafter – between late August and early September – as the sunshine duration and the temperature dictate when the blooming occurs, whereby their vegetative growth gets suppressed, resulting in less harvest.
If one tries to work around this problem by sowing early right before the rainy season arrives, then their vines grow too long, blocking the sun to the leaves below, which will prevent proper sunlight exposure and result in low harvest. To improve upon this approach, we still sow early but later trim the leaves up top before the flowers bloom. Due to the phenomenon of apical dominance, more side stems will then grow, which will improve the sunlight exposure and lead to more harvest.

In addition, we are applying another measure to improve the drainage of soil that involves digging trenches – also known as open ditches – so that the field does not retain excessive water. I along with my students also used to take bamboo brooms to the field after the rain to sweep the water out through the open ditches to see if it would make any difference, and the cultivation apparently improved. In terms of temperature, if it’s too warm at night, the plants’ respiration increases, consuming their photoassimilates in the process, which might impact crop harvest and quality.

So what do you find motivating about those research activities you have just explained to us?

Japan’s food self-sufficiency rate is now at around 38%. In order to improve the figure, we must raise our overall crop yield. In this connection, it is also crucial to maintain the country’s arable land. Currently, Japan has approximately 2,500,000 hectares of paddy fields and 2,000,000 hectares of other farmland according to some census. However, as these figures also include the farmland that is either fallow or desolated, the actual farmland in use is much less. So the total rice cultivation area has declined to 1,500,000 hectares now. Meanwhile, the self-sufficiency rates for wheat and soybeans are also low, at around 15% and 7%, respectively.
The staple food in Japan has historically been rice, and 94% of the agricultural land in Shiga Prefecture are paddy fields. Given such land composition, finding ways to grow field crops better remains a challenge. So it is incumbent upon us crop researchers to develop cultivars that have higher tolerance to excessive standing water, come up with new ways of field management to improve the drainage of soil, and make technical suggestions that are more acceptable to farmers. To me, this gives me such a significant sense of purpose, as I realize that the research we conduct helps our country maintain its arable land and might even do the same for the rest of East Asia where the conditions are similar.
Although there are a relatively large number of scientists studying the soybean – another legume – but not many are conducting research on the adzuki bean or the peanut, so this is another motivating factor for me to be able to educate and train scholars in this field. I also constantly pay close attention to the needs and wants of farmers. As long as we can clearly explain to the public the functions of our arable land that are conducive to the creation of a low-carbon society and also add value to the crops that we grow, the consumers might be receptive to the idea despite some unit price hikes, or at least this is how I am hoping our society will eventually turn out.

If climate change further escalates, would the research and the technology you have been working on be enough?

Recently, I participated in a symposium on climate change impacts affecting crops in Asia, which was attended by crop scientists from 23 different countries across Asia. Various discussions transpired at the event about how Japan and many other countries should formulate climate change scenarios, develop reliable cultivation techniques, and breed cultivars, etc.
As far as the crops’ harvest, quality, disease resistance, and tolerance to excessive standing water, etc. are concerned, I believe we have not yet fully discovered their potential, across all crop types at least. In order for us to make our contributions in agriculture to bring about a carbon neutral or carbon negative society, we must do more work to shed light on the crops’ full potential and develop such technology and techniques that will unlock it. It is our duty to do this work scrupulously, and this is the principle by which I remain committed to doing my research continuously.