16 November 2020

From farm to fork and back again – that’s how nutrients should travel in a cycle. Uno Wennergren, professor of theoretical biology, carries out research into how we can use fertiliser better in order to prevent both hunger and problems with eutrophication.

Uno Wennergren in front of a stable and a pile of fertiliser.Uno Wennergren is looking at how fertiliser can be transported back to agricultural fields. Photo credit Charlotte Perhammar“The world’s population is now 8 billion and forecasts point to 11 billion in 2100 – when those born today are pensioners. There’s no difficulty in growing food for 11 billion people on the cultivated area we currently use. The problem is not that the population is increasing, but that we do not use the necessary resources efficiently. A billion people who are today hungry are already demanding that we manage food production better”, says Uno Wennergren, professor in theoretical biology in the Department of Physics, Chemistry and Biology.

Hunger and starvation principally arise in rural areas, where the soil has been impoverished and gives harvests that are too small. The impoverishment depends to a large extent on farmers not being able to afford fertiliser, and the disappearance of nutrients from the soil each time the cultivated plants are harvested.Uno Wennergren.Uno Wennergren. Photo credit Charlotte Perhammar

“If these people could buy fertiliser for a period such that the harvests increased, they would be able to sell part of the harvest and buy fertiliser with the profit they make. But they are stuck at the wrong level and cannot climb out of poverty”, says Uno Wennergren.

In Sweden, the way in which nutrients are managed in agriculture plays a major role for other reasons. Let’s start at the beginning: plants need nutrients, such as nitrogen, phosphorus and potassium. We humans either eat the plants directly, or animals eat the plants and we then eat the animals. The excrement from both livestock and humans contains quantities of nutrients that can be used as plant fertiliser. But the same nutrients can, of course, also promote the growth of other plants, such as algae in water courses.

“Since the nutrients are needed in our food production, people are keen to force ever-increasing amounts of nutrients into the system. But if we use more fertiliser than the plants can absorb, the excess nourishment causes problems in the form of eutrophication of the sea and lakes. This is why we need to close the nutrient system as tightly as possible”, says Uno Wennergren.

It is for this reason that he is looking at how fertiliser can be transported back to agricultural fields such that the nutrients become elements in a circulation. His research group uses data from many different databases to determine where nutrients are needed in agriculture and the amounts that are needed. The researcher have, for example, detailed knowledge about which crops are cultivated in which fields all over Sweden, since farmers report this when they apply for EU support. They map the places where fertiliser is available, in other words the places where livestock is kept and where people live, since most of the food ends up in urban areas. Uno Wennergren uses mathematical models to calculate how much it would cost to transport the biofertiliser back to the fields in the most efficient manner. And it’s not just animal manure that can be used, but also human excrement, he points out.

“In the long-term, I believe that it will be necessary. We must be made to understand that it should be a system with the task of returning nutrients to agriculture”, says Uno Wennergren.

Artificial fertiliser and manure

Uno Wennergren and his doctoral student Usman Akram have studied conditions in Sweden and Pakistan. They conclude that it is possible to use the nutrients much more efficiently than at present. They have shown that we apply too much manure at certain places in Sweden, and compensate for this by using mineral fertiliser, also known as artificial fertiliser, at other places.

Using mineral fertiliser has two disadvantages. Some of the minerals, such as phosphorus, are obtained by mining, and the supply is limited. After being used in artificial fertiliser, some of the phosphorus ends up in the seas, and it is difficult to retrieve it from there.

The other problem is that when increasing amounts of these substances are forced into the system by human activity, some plants are forced out in competition with other, nutrient-hungry plants, which benefit. Biological diversity suffers.

“If we were to get to grips with this in a positive manner, we could reduce the use of mineral fertiliser dramatically. This means, in turn, that this finite resource would last for much longer. Furthermore, we would avoid problems with eutrophication”, says Uno Wennergren.

The analysis carried out by the researchers shows that some of the manure can be transported within Sweden without costing more than the cost of mineral-based fertiliser. But transporting all manure to places where it’s needed would be more expensive. Uno Wennergren believes that we cannot expect farmers to bear the complete cost. This is a question that society must deal with, either by political decisions that use both carrot and stick, or by consumers choosing products that are part of smart fertiliser management.

“It’s all connected”

The researchers had initially intended to analyse only Sweden, but decided to widen their horizon to include Pakistan, mainly from pure curiosity. Their eyes were opened when they saw the differences between the two countries. A global perspective was introduced into the questions of nutrients.

“People die of starvation in Pakistan. Their problems with manure are on a completely different level than in Sweden. The advantage is that transport is cheaper in Pakistan, so it makes financial sense to move manure around. If manure could be used in an efficient manner in Pakistan, famine could be eradicated.”Uno Wennergren.Uno Wennergren. Photo credit Charlotte Perhammar

Uno Wennergren calculates what is known as the “harvest gap”, which is the difference between potential harvest and actual harvest, for the global picture.

“We see that essentially those countries with good access to fertiliser and good harvests continue to use increasing amounts of fertiliser. And vice versa – in countries with small harvests and an increasing harvest gap the use of fertiliser in cultivation is falling. This problem is reflected at the global level, and it will be an enormous challenge for the world.”

This is because even if most of us don’t go around thinking about nutrient circulation or food production, these issues are linked to other major questions. Increasing hunger and starvation are a strong driving force for refugee crises, conflicts and war. And the way in which humans produce food has an impact on other species.

“If fertiliser is not applied where it’s needed, the soil becomes poor in nutrients, and this leads farmers to take new land for cultivation. The biggest cause of the loss of species and biological diversity today is humans taking over the habitats of animals and plants”, says Uno Wennergren.

Reversing the trend will take many decades, even if we start now.

“We are in a situation where this can be solved. We have all the tools we need, and the opportunity to deal with long-term population growth to eleven billion. But it needs a willingness to get to grips with these challenges. Before my time on earth is up, it will become clear whether we’re following the right pathway.”

Translated by George Farrants

More about the research

The Agtech 2030 research programme 

• Agtech 2030 is an initiative intended to establish an innovation centre for tomorrow’s agriculture.
• Around 20 organisations are behind the initiative, including Linköping University, Region Östergötland, Rural Economy and Agricultural Societies, and Vreta Kluster.
• The programme focusses on new concepts based on, for example, sensors, digital technology and AI, and on new collaborations and ways of doing business.
Cover of publication 'Closing nutrient cycles'
Usman Akram (2020)

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