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在衣阿华土壤上采12个草原土体样品和耕种了120年的土壤,研究植被的影响。研究的焦点聚集在土壤物质分组的和未分组的有机质。气候、母质、时间和坡度尽可能保持一致。湿草原衍化的软土表层比森林衍化的淡色表层含有较多的有机C和全N。耕种的表土通常比对应表土含有机C和全N较低,但只有在软土表层耕种后其C/N比率显著降低。虽然在未耕种土壤上大多数有机C和全N是与细粉砂和粗粘粒部分结合在一起。但种植后产生相应的迁移,有机质从砂粒和粉砂部分移向细粘粒部分。耕种土层各颗粒大小组分中有机物质的HA/FA,比率,通常都低于未耕种土层。各颗粒大小组分中腐殖物质的E_4/E_6比率表明,软土表层比淡色土层含有较大的有机分子。耕种对土壤有机质的影响的解释,必须慎重,因为对未耕种之处有着其它的农业影响。
Twelve samples of grassland soil were collected from Iowa soils and cultivated for 120 years so as to study the effects of vegetation. The focus of the research is on organic matter that is grouped and unclustered in soil material. Climate, parent material, time and slope are as consistent as possible. The wetland derived soft soil surface contains more organic C and total N than the forest-derived pale surface. Cultivated topsoil usually contains less organic C and less total N than the corresponding topsoil, but its C / N ratio is significantly reduced only after topsoil cultivation. Although most organic C and total N in uncultivated soils are associated with fine silts and coarse clay fractions. However, after planting there is a corresponding migration, organic matter from the sand and silt moving part of the small clay. HA / FA ratio of organic matter in each particle size fraction of cultivated soil is usually lower than that of uncultivated soil. The E_4 / E_6 ratio of humic substances in each particle size fraction indicates that the surface of soft soil contains larger organic molecules than the pale soil layer. The interpretation of the effect of cultivation on soil organic matter must be interpreted with caution, as there are other agricultural effects on uncultivated land.