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Medical imaging helps reveal lasting impacts of soil compaction

Date:
January 14, 2014
Source:
American Society of Agronomy (ASA)
Summary:
While subsoil compaction is easy to ignore because it’s hard to see, it definitely deserves more study.

3-D images of the macropore system in 10 cm-diameter, 8 cm-high soil cores taken from a heavy clay soil in Finland. Left: Control (non-compacted) soil. Right: Soil from plots where heavy machinery drove over the ground in an experimental treatment 29 years earlier.
Credit: Images obtained from x-ray, computed tomography (CT) scans by Mathieu Lamandé.

The large, air-filled spaces, or "macropores," in untilled soil often resemble the branching vessels of the human circulatory system. Taking advantage of this similarity, a team of Nordic researchers led by Per Schjønning combined computed tomography (CT) scanning with traditional measurements of air exchange to "diagnose" the long-term impacts of soil compaction on the hidden, but vital, soil pore network.

In farm settings, soil can become compressed and unnaturally dense when heavy farm machinery is driven over it. But what the system of pores looks like in compacted soil hasn't been well studied.

When the Nordic scientists examined cores of compacted, heavy clay subsoil from a research site in Finland, they found the macropores were greatly affected compared with a non-compacted, control soil. In particular, the compacted soil contained mostly long, vertical "arterial" pores, or pipes, with significantly fewer "marginal" pores branching from them.

The findings appeared in the Nov.-Dec. 2013 issue of the Soil Science Society of America Journal.

Compaction also reduced the size of the vertical arteries, and just as in the human body, this constriction of the soil's "circulatory" system can have ill effects. Blocked and narrowed pores likely impede the diffusion of air through bulk soil, the scientists say. The dominance of vertical pipes in the compacted soil also suggests that water flows mostly downward, with relatively little reaching the surrounding soil matrix. Both of these changes can reduce crop productivity. But most troubling to the researchers was how lasting the impacts of compaction appear to be. In the study, the group examined soil cores taken from a depth of 0.3 to 0.4 meters (0.9 to 1.2 feet) in plots where 30 years earlier a heavy tractor-trailer drove over the ground four times in an experimental treatment. (Only smaller farm equipment was used in subsequent years.) Despite all the elapsed time, macropores in the compacted subsoil were still highly altered compared with control soils, indicating a poor ability of this heavy clay soil to recover its original structure. What's more, the damage was done by wheel loads (3.2 Mg per tractor rear wheel and 4.8 Mg per trailer wheel) that are considerably lower than those used in agriculture today.

What this all says is that while subsoil compaction is easy to ignore because it's hard to see, it definitely deserves more study, say the researchers. And what better to help diagnose this hidden problem than CT -- a medical instrument that detects equally stealthy problems in the human body?


Story Source:

The above story is based on materials provided by American Society of Agronomy (ASA). Note: Materials may be edited for content and length.


Journal Reference:

  1. Per Schjønning, Mathieu Lamandé, Feto E. Berisso, Asko Simojoki, Laura Alakukku, Rune R. Andreasen. Gas Diffusion, Non-Darcy Air Permeability, and Computed Tomography Images of a Clay Subsoil Affected by Compaction. Soil Science Society of America Journal, 2013; 77 (6): 1977 DOI: 10.2136/sssaj2013.06.0224

Cite This Page:

American Society of Agronomy (ASA). "Medical imaging helps reveal lasting impacts of soil compaction." ScienceDaily. ScienceDaily, 14 January 2014. <www.sciencedaily.com/releases/2014/01/140114130703.htm>.
American Society of Agronomy (ASA). (2014, January 14). Medical imaging helps reveal lasting impacts of soil compaction. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2014/01/140114130703.htm
American Society of Agronomy (ASA). "Medical imaging helps reveal lasting impacts of soil compaction." ScienceDaily. www.sciencedaily.com/releases/2014/01/140114130703.htm (accessed July 28, 2014).

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