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San Joaquin is an officially designated state insignia, the state soil of the U.S. state of California. The California Central Valley has more than 500,000 acres (2,000 km²) of San Joaquin soils, named for the south end of that valley. This series is the oldest continuously recognized soil series within the State. It is one of California's Benchmark Soils, and a soil profile of it is displayed in the International Soil Reference and Information Centre's World Soil Museum. The San Joaquin series became the official state soil on August 20, 1997,〔(【引用サイトリンク】 publisher = Professional Soil Science Association of California )〕 the result of efforts by students and teachers from Martin Luther King, Jr. Middle School in Madera, natural resource professionals, the Professional Soil Scientists Association of California, legislators, and various state universities. These soils are used for irrigated crops, such as wheat, rice, figs, almonds, oranges, and grapes, and for pasture and urban development. San Joaquin soils formed in old alluvium on hummocky topography. A cemented hardpan a few feet beneath the surface restricts roots and water percolation. San Joaquin soils are classified in USDA soil taxonomy as fine, mixed, active, thermic abruptic durixeralfs. ==Soil profile== *Surface layer is brown loam. *Upper subsoil is brown loam, lower subsoil is brown clay. *Substratum is light brown and brown, indurated duripan with 70 to 90 percent silica-sesquioxide cementation. 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「San Joaquin (soil)」の詳細全文を読む スポンサード リンク
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