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Soil under pressure

The majority of the food we eat originates directly or indirectly from the soil. But soil fertility is under threat because of the way we treat it. This is a topic to which much research is being devoted at Aarhus University, working alongside the agricultural industry and the authorities.

2015.07.01 | Janne Hansen

If we do not take good care of our soil resource, we risk destroying it so that it loses its ability to grow crops. Photo: Per Marcussen

Many of us may have a tendency to take the soil a little for granted. It has always been there and does not seem likely to disappear any time soon. We must, however, be better at cherishing it, because as they say, we do not inherit the earth from our ancestors, but borrow it from our children.


Soil has many important functions. Virtually all the food we eat comes originally from the soil, either directly in the form of crops that we eat or indirectly in the form of feed for our livestock. The soil is a growth medium for crops for food, feed, fibre and energy.


The soil also fulfils many other important functions. It filters water to keep our groundwater reservoirs pure. It converts facilitates the turnover of plant residues and manure so important nutrients are supplied to the crops and not lost to the environment.


The soil is not a free-for-all

There is in other words a need to protect the soil and ensure that its many vital functions will endure in the future. The soil is, however, under intense pressure from a variety of factors that affect its fertility. Poorer fertility means declining yields – and this at a time when the world population is growing and increasingly demanding a sustainable supply of foods.


Scientists from Aarhus University are helping to highlight the problems and create knowledge that can form the basis for sound practices and legislation.


- The threats to arable land should be taken seriously. We must not put the basis for the existence of future generations at risk, says Senior Scientist Per Schjønning from the Department of Agroecology.


Soil is compacted

Globally, the human use of land has led to processes such as erosion, soil compaction, desertification, salinisation, urbanisation, pollution and loss of organic matter and biodiversity. In Denmark, we have three main problems with arable land:


- Soil compaction under the plough layer

- Erosion due to wind, water and soil tillage

- A decreasing organic matter content


For all the threats it is true that following a change it takes a long time for the soil to recover.


Heavy farm machinery on soil causes soil compaction below the plough layer and scientists from the Department of Agroecology have shown that these injuries are largely permanent.


- The very heavy machinery used today carries a higher risk that the compaction will reach ever deeper soil layers, says Per Schjønning. He is the Danish project manager of the five-year EU project RECARE that is preparing the ground for sustainable solutions in farming, with direct inputs from farmers and other stakeholders.


The project has assembled a multidisciplinary team to uncover the severity and extent of the threats to soil and to find innovative solutions to prevent further land degradation in Europe. Scientists from 27 different organisations and companies, including Aarhus University and Kongskilde Industries A/S, share knowledge about actual soil conditions and define measures that can be used to address the main problems.


Wind, water and tillage erode the soil

Another major problem that scientists at the Department of Agroecology are working with is erosion. Wind, water and tillage erode our farmland. Erosion is widespread in Denmark and can reduce soil quality and yield potential and threaten the environment.


There was a time when about 500,000 ha of agricultural land was exposed to wind erosion and where soil losses of more than 10 tonnes of soil per ha were not considered unusual. This has improved greatly since the widespread introduction of winter crops, and windbreaks have considerably reduced the risk of wind erosion.


Erosion caused by water can still be a problem. This depends on a complex interaction between topography, climate, soil type and cultivation practices.


Erosion as a result of soil tillage occurs when a hilly area is ploughed, or otherwise managed intensively. Tillage erosion acts as an efficient conveyor belt moving soil from hilltops to hollows in the field, without changing much in the middle part of the slopes. Soil loss is typically 20 tonnes per ha per year. Studies show that erosion mainly occurs in fields with winter crops and ploughed fields.


- On heavily eroded areas, water and wind erosion causes the loss of fine-grained material, organic matter and nutrients. This is detrimental to the soil structure, to its water-holding capacity and the environment. In the long term it will affect the yield potential. Since tillage erosion occurs across all hilly, cultivated terrain and results in a significant redistribution of land, particularly this type of erosion can in the long term result in severe soil degradation, says Senior Scientist Goswin Heckrath from the Department of Agroecology.


For more information please contact: Senior scientist Per Schjønning, Department of Agroecology, e-mail: per.schjonning@agro.au.dk, telephone: +45 8715 7725


This article has been published in DCA's annual report, which can be read here.

DCA, Technology, Agro