Soil is a resource, and wisdom is needed to utilize it sustainably

 October 5, 2020

Soil is a resource, and wisdom is needed to utilize it sustainably

Masahiko Kato
Associate Professor, School of Agriculture,
Meiji University
 

In recent years, due in part to the spread of the SDGs, interest in sustainability is growing in a variety of fields. Soil, too, is being understood as a resource for food production in the world. A framework for international cooperation to support the world’s population into the future has been established, and 2015 was designated as the International Year of Soils. Soil, on which we usually tread without an awareness, is something very important to the human race.
Soil is an important resource, and people need to take appropriate measures

What do you think of when you hear the word “soil”? People with an interest in agriculture perhaps think of the rice and vegetable fields used to grow crops, while for people living in the cities, it is probably not something which feels very familiar to them.

However, concrete and asphalt are built on top of soil. In fact, we cannot live apart from the ground.

We can say that soil is a resource for the human race, not only in order to produce crops, as we do through agriculture, but also in terms of the environments in which we live.

If we are aware that soil is a resource, we understand that there is a possibility that it may become unusable.

Of course, soil will not be exhausted like oil, but it is possible that it may become unsuitable as an environment in which we can live or produce agricultural crops.

For example, there are problems with pollution which make it impossible for humans to live on the land, or a decline in fertility which makes it less productive for crops. Moreover, we humans are the ones causing these kinds of problems.

If people stopped getting involved and let the soil revert to its natural state, then, would the problems be resolved? In fact, this would not necessarily be the case.

For example, people who live in cities tend to think of a vista of rice fields as a natural scene, but nothing could be further from the truth. Rather, agricultural land is an extreme example of man-made land. The soil is plowed, fertilizer is sprinkled onto it, and weeds which grow wild are removed: in other words, the soil of agricultural land is exceedingly artificial soil.

Originally, soil refers to the portion of the earth’s surface layer which is made up of particles. The rocks which were in this area of land were weathered over long periods to form its base. A variety of conditions such as the climate, topography, and precipitation are added to such base, so that even if having a similar color and form, the soil in each area has different properties.

Some areas of land are very fertile, and crops grow well there. On the other hand, there are areas which are not suitable for growing crops.

For example, in areas where the volume of evapotranspiration is greater than that of precipitation, salts accumulate on the soil surface, and few plants are able to grow there. Furthermore, even in naturally fertile areas, if people repeatedly cultivate the same crops, the productivity of the land will eventually decline.

In other words, the soil of agricultural land is not left to nature; rather, people are continually doing something to it to “make” soil which produces more crops.

If we want to continue to use agricultural land as a resource for crop production, then, this means that we have to take appropriate measures towards the soil.

Moreover, the same is true not only of agricultural land but also of the environments in which we live. If we once pollute the soil, we cannot just leave the task of returning it to a healthy state up to nature: people have to take some kind of measures.

I believe that understanding soil as a resource in this way, thinking of appropriate measures to allow us to use it sustainably, and passing it on to the next generation are very important issues for us.
A correct understanding of the physical, chemical, and biological nature of soil is important
What are appropriate measures? People may tend to think, for example, that we should use lots of fertilizer in order to raise soil fertility and increase the volume of crops produced; but just using a lot is not the solution.

It is necessary to think about soil composition and add nutrients to make it suitable for crop production.

Of course, farmers have methods which have been passed down over generations, and I am sure that they are using measures which are effective for that area of land.

However, in this time when various changes are taking place in the environment, it is also important to have accurate knowledge: for example, a correct understanding of the physical, chemical, and biological nature of soil.

In other words, in physical terms, this means thinking about improving the aeration, water retention, and permeability of the soil, making it easier for crops to put down roots.

In chemical terms, it means thinking about the appropriate soil acidity and base balance, and high ability of nutrient retention.

In biological terms, it means thinking about the conditions in which diverse soil organisms and microbes exist in a stable mix.

I believe that possessing this kind of knowledge and understanding soil as a resource leads to the conservation of highly productive soil resources, as well as to their sustainable utilization.

In addition, my research includes rehabilitation of polluted soil. An example is soil contaminated with toxic metals. If materials which react with these toxic metals are mixed into the soil, they make the toxic metals less readily soluble. This kind of research is an application of physical chemistry.

What we are aiming for is certainly not untouched nature. We aim to think about what we can do in order to conserve an environment for humans to live in and soil resources that can sustainably produce the food which we need to live.
Reuse of byproducts and conservation of soil resources: balancing these two elements leads to sustainable utilization of the soil
Byproducts refer to things which occur secondarily alongside production of the target product. Vegetable waste are among agricultural byproducts.

They also include sewage sludge, livestock manure, food waste, and byproducts of manufactured goods such as the slag emitted by the iron and steel industry (which occurs secondarily when metal is refined).

I think that reusing byproducts like these in the soil is also necessary. When we think of soil as a “resource,” it may be better not to use such unknown byproducts, since there is a risk of decreasing the value of soil as a resource.

However, I believe that we are entering an era in which we will think hard about how to balance both of these apparently contradictory elements, and utilize soil sustainably. One reason for this is that a large volume of byproducts will be generated. Until now, the byproducts which we do not need have mainly been disposed of through landfill, but we are about to run out of landfill sites within Japan.

Another reason is that we have almost depleted the resources used for agricultural fertilizers globally.

Agricultural fertilizers such as phosphorus and potassium are actually made from minerals. Since these minerals are running out, some producing countries are starting to treat them as strategic resources, in the same way as petroleum and rare metals. This is an extremely serious problem.

For example, we produce enough rice to meet domestic demand, but all the fertilizer needed to do so is in fact imported from overseas. If this were to disappear, the situation would be grave. We might become unable even to get enough rice domestically.

However, even if, for example, we were to mix all the byproducts containing nutrients, such as raw garbage – all the unused resources – indiscriminately into the soil of agricultural land, this would certainly not be a solution.

This raw garbage contains pathogens, the seeds of weeds, and so on. Scattering these would be a kind of soil pollution.

Moreover, since raw garbage includes a lot of readily decomposable organic matter, if it is mixed into the soil, this decomposition proceeds rapidly within the soil, decreasing the oxygen in the soil and making it harder to grow crops.

However important the reuse of byproducts may be, decreasing the value of soil as a resource is a problem. There are ways to turn vegetable scraps and other agricultural byproducts into organic fertilizer such as compost by allowing them to ferment. This is certainly one effective method.

I think that it is necessary to clarify what kinds of byproduct we can use without decreasing the value of soil as a resource, and how they can be used. I also think that it is necessary to make problematic byproducts usable.

In other words, finding methods of using the nutrients in byproducts well is a way to address the depletion of fertilizer resources globally, and will lead to the conservation and sustainable utilization of soil resources.

The issue of the falling birthrate and declining population in Japan makes it harder to notice, but the world’s population is increasing. It is said that there will not be enough land to produce the crops needed to feed the population increase by 2050.

In the future, it may become possible to produce a large volume of crops without land, but this remains very difficult at present.

Again, we cannot live apart from the earth. Moreover, the sustainable utilization of soil resources is impossible unless we humans take appropriate measures.

I believe that greater interest in these issues among the public will lead to improvements in the food and environmental problems which we face now and into the future.



* The information contained herein is current as of September 2020.
* The contents of articles on Meiji.net are based on the personal ideas and opinions of the author and do not indicate the official opinion of Meiji University.
* I work to achieve SDGs related to the educational and research themes that I am currently engaged in.


Masahiko Kato
Associate Professor, School of Agriculture, Meiji University
 
Research fields:
Soil science, geo-environment science

Research themes:
The development of techniques for the restoration of polluted urban soil and ground to a usable state; the development of techniques for the effective utilization in soil of international resources such as fertilizer

Main books and papers:
◆Enhancing pyromorphite formation in lead-contaminated soils by improving soil physical parameters using hydroxyapatite treatment, Science of the Total Environment (2020)
◆Feature of lead complexed with dissolved organic matter on lead immobilization by hydroxyapatite in aqueous solutions and soils, Chemosphere, Vol. 249, 126122 (2020)
◆Arsenic release from marine sedimentary rock after excavation from urbanized coastal areas: Oxidation of framboidal pyrite and subsequent natural suppression of arsenic release, Science of the Total Environment, Vol. 670, 752–759 (2019)


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