Soils are the foundation that supports plant growth and they are also important as the basis for agriculture. The study of soils, which are complex materials of minerals, organic matter, air, water, and organisms, is actually a very deep subject. Its complexity and difficulty may contribute to its attraction.
On what kinds of soil do plants grow well?
Addressing the effective use of finite phosphorus resources.
Dr. Nagaoka's laboratory conducts researches which analyze and utilize the role of plants and soil ecosystems in improving both plant production and environmental conservation, in other words, towards achieving sustainable plant production.

Although the main object of the research is the "soil", the research is based on analyzing both soils and the plants, since the goal is to comprehensively analyze and clarify the relationship between the productivity of the plants grown in soils and their nutrient absorption and composition (quality).
"Plant researchers tend not to look at soils very much, and in soil science, researchers tend to classify and analyze only the soil," says Dr. Nagaoka, "but we have been studying for a long time looking at both soils and plants.” The point is to explore "how the soil affects the plant."

“We hope to enable effective soil management for sustainable plant production by taking into account the physical and chemical properties of soils, as well as the organic matter that is closely related to microorganisms.”
In particular, the focus of the current research is the study of phosphorus.
Nitrogen, phosphate, and potassium are said to be the three elements of fertilizer and are considered to be the most important of the nutrients (essential elements) that plants need to grow. Among them, the phosphate is easily fixed and adsorbed to the soil, and also binds with aluminum, iron and calcium in the soil, making it less soluble.
“When plants absorb water from their roots, they also absorb the nutrients that are dissolved in soil water, so nutrients need to be dissolved in soil water for plants to absorb them. In the case of phosphorus, it is often in forms that are not dissolved easily, so if there is not enough available phosphorus in soils, the fertilizer absorption rate becomes low.”
For this reason, phosphorus, which has come to be consumed in large quantities by modern agriculture, being applied in large doses as a fertilizer, is an important and finite resource that is in danger of being depleted in the near future. Thus, various measures are being researched to ensure its effective use.
  Therefore, Dr. Nagaoka is currently analyzing the functions of phosphorus-dissolving bacteria that can dissolve insoluble inorganic phosphorus and microorganisms involved in the degradation of persistent organic phosphorus (e.g. phytate-degrading bacteria), and is engaged in research aimed at allowing crops to effectively use phosphorus accumulated in soils.
“Composted waste such as food residue (food-derived waste) and livestock waste contain a significant amount of nutrients, which we try to successfully circulate. In my study, I am putting organic matter into the soil. As a result, soil microorganisms increase. Using the power of microorganisms to mineralize and dissolve phosphorus compounds, we are making phosphorus soluble and easily absorbable by the plants. This is what I am researching.”

In the fields, plots amended with organic matter (compost) or with chemical fertilizers have been set up, and the long-term effects on crop productivity, nutrient absorption, soil physicality, chemistry, and microorganisms are being studied.
Soil study is indeed quite difficult.
It is also interesting to make discoveries involving diverse phenomena.
“There are a lot of things you can't tell by just looking at the soil. Yet, if you look at the plants that are growing in fields, you'll know what the soil is lacking. And if the results of the analysis are consistent with what the soil seems to be lacking, then we can say that this is probably the cause.” The research method that focuses on both plants and soils has this kind of advantage. The results of the study are expected to be used to create guidelines for cultivation and soil management in the future.

Dr. Nagaoka originally specialized in organic chemistry of natural products, and he says he prefers chemical analysis to looking into a microscope. Therefore, he describes his interest in this study as follows.
“Soils are very heterogeneous and diverse materials, so it's probably not just one aspect that's important. The analysis organizes conditions created through the involvement of various materials and aspects, and we identify them one by one. The interesting point of this research is the process of identifying important things among diverse aspects.”
  He also adds that the difficult part of this study is the complexity of the soil.
“If the soil was like air, we would be able to find out its composition right away, but it's quite difficult with soil because there are many things involved. There are microorganisms in it, and although it is made of minerals, the materials are totally different, and the soil composition depends on what kind of fertilizer has been used in a given area in the past, what kind of plants have been grown, and where it is located. To actually look into their relationships, you have to study the soil under the same conditions. It is easy to create the same conditions if we use pots, but as the scale becomes larger including fields, plots, and farms, finding what we are looking for becomes increasingly difficult.”
Because the study often uses soils of Hiroshima as its subject, the research team mainly uses the granitic regosols that is widespread in Hiroshima. Granitic regosols are immature soils formed from weathered granite, which also has some troubling properties, according to Dr. Nagaoka.
“When compost is added to granitic regosols, the small particles of the soil become aggregates and improve water retention and nutrient retention. But it seems to decompose quickly, so a problem is that even when organic matter is mixed with the soil, it doesn't stay and accumulate in the soil very well.”
In addition, it can be weather dependent when growing plants in fields. “These days, cultivation often goes wrong, so I am thinking that maybe I shouldn’t be just working on the soil. I think I should keep climate change in mind as well.”
Many members of the laboratory love plant cultivation.
They conduct extensive research while having fun!

  “Soil sounds conservative, doesn’t it? Soil science is the foundation of agronomy, and it's an essential field, but it doesn't have a very glamorous image. It is a field where great inventions and discoveries don't appear very often," says Nagaoka, laughing.

Many of the students who gather at Dr. Nagaoka’s laboratory are interested in cultivation. Since there are not many laboratories that cultivate plants, students interested in agronomy get together here and devote themselves to the surprisingly hard work of cultivation.

Dr. Nagaoka said he expects young people to have an interest in and understanding of the soil.
“I hope that anyone who is interested in growing crops will understand the importance of soil. Soil is a very important foundation of agriculture. I think another feature of our research is that we actually deal with a diversity of things, such as analysis and evaluation of the soil environment, relationships with plants, and microbes. If you are interested in the world of soil, please come to our laboratory.”
Toshinori Nagaoka
Associate Professor
Laboratory of Plant Environment Analysis

April 1, 1991 to March 31, 2002 Research Associate at School of Applied Biological Science, Hiroshima University
April 1, 2002 to March 31, 2003  Research Associate at Graduate School of Biosphere Science, Hiroshima University
April 1, 2003 to March 31, 20019  Associate Professor at Graduate School of Biosphere Science, Hiroshima University
April 1, 2007 to March 31, 2019  Associate Professor at Graduate School of Biosphere Science, Hiroshima University
April 1, 2019 to present Associate Professor at Graduate School of Integrated Sciences for Life, Hiroshima University

Posted on mar 3, 2021