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Background

A plant with it's roots. It is difficult to make good pictures of roots as they are either in the soil and thus hidden or washed out of the soil and ruined. Photo: Kristian Thorup-Kristensen

As frequently emphasized, the increasing global population and wealth leave us with a huge challenge for producing enough food during the century ahead, with a projected increase in demand of about 70% by 2050 (FAO). There is no scope for solving these problems by increasing the agricultural land area. Agricultural land is being lost due to urbanization, soil degradation and climate change, and most of the agriculturally valuable land on earth is already in use. Though agricultural area is still increasing in some areas, the total arable land area of the world reached its maximum around 1990 (FAOSTAT) due to these processes. Any attempt to increase agricultural land into areas currently left to nature occur at severe environmental costs, and many developed countries, including Denmark, strive to increase the proportion of land in nature.

As we cannot increase the agricultural area, production has to increase through increased efficiency and intensification of production. The available arable land per person has dropped from 0.41 hectares in 1961 to 0.22 hectares in 2010 (FAO), and will continue to decline in the years ahead. The intensification needed to handle this situation will require high resource input, and will cause further environmental problems and increase the use of limited resources. 

Within this picture, we see the increased exploitation of subsoil resources by crops as one of the ways whereby we can increase food production in a sustainable way. It will allow us to increase production without having to add further resources. The use of deep rooting crops can potentially improve environmental performance and resilience of food production and maintain or even improve agricultural soil quality due to more permanent soil cover and higher organic matter input to the soil. These effects can also contribute to climate change mitigation through increased carbon storage in the soil, including increased storage in deeper soil layers (Harper and Tibbett, 2013) where stored carbon may be more stable.

Challenges

Current agricultural systems do not utilize subsoils efficiently. The maximum rooting depths of common crops range from 0.5 to 2.5m, much less than the potential rooting depth of many plant species (Canadell et al., 1996).

A main limitation arise from the short life span of crop plants giving them too short time to develop deep rooting, and the maximum rooting depths are only maintained through short periods at the end of the crop growth period (Thorup-Kristensen et al., 2009; Thorup-Kristensen et al., 2012). During most of the year, the soil in arable cropping systems is either without crop and roots or covered by a young crop, which still only have shallow rooting.

Adapting cropping systems by inclusion of deep rooted cover crops (Figure 1) or by growing more crops with longer growing seasons may substantially increase the crop exploitation of deeper soil layers (Thorup-Kristensen et al., 2012).

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Impact and effect

Photo from the project

The overall objective of the project is to develop results, methods and ideas for the development of sustainable agricultural systems for the future, through increased exploitation of resources from deep soil layers.

The expectation is that the project will be able to do this, and to contribute to further research and development in this direction.

Deep rooting will contribute to development of systems which:

  • Need less resource input in terms of plant nutrients and irrigation water
  • Loose less plant nutrients to the environment
  • Give higher productivity and higher production stability, as resource availability from deeper soil layers is less affected by short term variability e.g. in water supply
  • Give stronger climate change mitigation through increased storage of carbon in the subsoil

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