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Soil compaction, also known as soil structure degradation, is the increase of bulk density or decrease in porosity of soil due to externally or internally applied loads.〔Alakukku, Laura (2012). Soil Compaction. In: Jakobsson, Christine: Ecosystem Health and Sustainable Agriculture 1: Sustainable Agriculture. Uppsala University. URL: www.balticuniv.uu.se/index.php/component/docman/doc_download/1256-chapter-28-soil-compaction- (accessed November 14th 2014).〕 Compaction can adversely affect nearly all physical, chemical and biological properties and functions of soil.〔Whalley, W.R., Dumitru, E. & Dexter, A.R. (1995). Biological effects of soil compaction. Soil and Tillage Research, 35, 53–68.〕 Together with soil erosion, it is regarded as the "costliest and most serious environmental problem caused by conventional agriculture."〔FAO (2003). Soil Compaction - an unnecessary form of land degradation. p. 2. URL: http://www.fao.org/ag/ca/doc/Soil_compaction.pdf (accessed November 15th 2014)〕 In agriculture, soil compaction is a complex problem in which soil, crops, weather and machinery interact. External pressure due to the use of heavy machinery and inappropriate soil management can lead to the compaction of subsoil, creating impermeable layers within the soil that restrict water and nutrient cycles. This process can cause on-site effects such as reduced crop growth, yield and quality as well as off-site effects such as increased surface water run-off, soil erosion, greenhouse gas emissions, eutrophication, reduced groundwater recharge and a loss of biodiversity.〔Batey, T. (2009). Soil compaction and soil management – a review. In: Soil Use and Management, 12, 25, 335-345, see page 339-340. Doi. 10.1111/j.475-2743.2009.00236.x〕 Unlike salinization or erosion, soil compaction is principally a sub-surface problem and therefore an invisible phenomenon.〔FAO (unknown). Conservation of natural resources for sustainable agriculture: what you should know about it. See page 2. URL: http://www.fao.org/ag/ca/training_materials/cd27-english/sc/soil_compaction.pdf (accessed November 14th 2014).〕 Special identification methods are necessary to locate, monitor and manage the problem appropriately. Top soil compaction is considered partly reversible and its occurrence controllable.〔FAO (unknown). Conservation of natural resources for sustainable agriculture: what you should know about it. See page 2. URL: http://www.fao.org/ag/ca/training_materials/cd27-english/sc/soil_compaction.pdf (accessed November 14th 2014)〕 Subsoil compaction, however, is regarded as the major problem because it can be permanent, meaning the pore functions can potentially not be restored after deterioration.〔Hakansson, I., Reeder, R. (1994). Subsoil compaction by vehicles with high axle load—extent, persistence and crop response. In: Soil and Tillage Research, 29, 2-3, page 277-304.〕 Since farmers in modern intensive agriculture depend on heavy machinery and therefore cannot completely avoid compaction, soil compaction management approaches focus on mitigation.〔Batey, T. (2009). Soil compaction and soil management – a review. In: Soil Use and Management, 12, 25, 335-345, see page 342. Doi. 10.1111/j.475-2743.2009.00236.x〕 Attempts to mitigate soil compaction include biological, chemical and technical approaches. Long-term public policies can tackle the underlying reasons for soil compaction. For instance, subsidies for low-tech agriculture may decrease heavy machinery use on the field, and educational programs aiming at slowing population growth can lower the pressure on agriculture caused by population size. ==History and current state== Soil compaction is not a recent issue. Before the beginning of mechanized agriculture, the usage of plough-pans was associated with soil compaction.〔Batey, T. (2009). Soil compaction and soil management – a review. In: Soil Use and Management, 12, 25, 335-345. See page 335. Doi. 10.1111/j.475-2743.2009.00236.x〕 However, multiple studies have shown that modern farming techniques increase the risk of harmful soil compaction.〔Stalham, M.A., Allen, E.J. & Herry, F.X. (2005). Effects of soil compaction on potato growth and its removal by cultivation. Research review R261 British Potato Council, Oxford.〕 The historic data basis for global soil compaction is generally very weak as there are only measurements or estimates for certain regions/countries at certain points in time. In 1991, it was estimated that soil compaction accounted for 4% (68.3 million hectares) of anthropogenic soil degradation worldwide.〔Oldeman, L.R., Hakkeling, R.T.A. and Sombroek, W.G. (1991). World map of the status of human-induced soil degradation. An explanatory note. ISRIC, Wageningen, UNEP, Nairobi.〕 In 2013, soil compaction was regarded a major reason for soil degradation in Europe (appr. 33 million ha affected), Africa (18 million ha), Asia (10 million ha), Australia (4 million ha), and some areas of North America.〔Nawaz, M. Bourrié, G. and Trolard, F. (2013). Soil compaction impact and modelling: a review. In: Agronomy for Sustainable Development 33: p. 291-309.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Soil compaction (agriculture)」の詳細全文を読む スポンサード リンク
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