与永久性草地相比长期裸露侵蚀对英国Bridgnorth砂壤的影响

 对位于英国东Shropshire的Hilton试验点中,已裸露12年的坡地侵蚀小区内的Bridg-north砂壤进行调查分析,并与小区相邻的自然草地作比较,结果显示,裸露砂壤土的有机质和大多数营养元素的含量显着低于草地;草地的有机质含量较裸地高2.15倍;草地含有较高比例的粗砂(0.355～2.0mm),尤以0.500～1.0mm部分较为突出,以及较少的粘粒(<0.002mm)和石砾(>2mm);说明,粗砂易于流失,Bridgnorth砂壤被长期侵蚀后,粗砂趋于减少,粘粒、石砾所占比例则逐渐增加.结果同时还指出,裸土的pH值不断降低,草地的粘粒和粉粒含量与坡度呈显着正相关,粗砂与坡度则负相关,这与福林等人研究的裸土的情形相似.以上结果表明,如果坡地被长期暴露,并且不投入任何营养物质,土壤肥力将迅速下降,质地发生变化,而种草可以保持和改善土地生产力,阻止土壤质地的变化.

Effect of Long Time Erosion on the Properties of Loamy Sand Soils of the Bridgnorth Series Compared with Permanent Grassland

The properties of loamy sand soils of the Bridgnorth series were investigated after being bare for 12 years on runoff plots and compared with adjacent grassland at the Hilton experimental site, east Shropshire, UK. Soil organic matter and most nutrients (Al₂O₃, Ca₂O, MnO, Na₂O, P₂O₅, SiO₂ and Cu) were significantly lower in bare soil than in grassland soil. Include mean values soil organic matter was 2.15 times higher in grassland than in bare soil, with highest values on the bottom of the slope on both bare and grassed plots. The grassland soil contained relatively higher coarse sand (0.355-2.0 mm), particularly 0.5～1.0 mm fraction, and less clay (<0.002 mm) and coarse (>2 mm) fractions than bare soil. This suggests that the coarse sand was selectively removed by erosion; the loamy sands tend to decrease coarse sand and increase clay content after prolonged erosion. The results indicated that clay and silt tend to be transported down slope. Significant positive linear relationships between clay, fine silt and slope, and a significant negative linear relationship between sand and slope were found in grassland soil. Furthermore, there was a trend for soil pH to be less on bare soil. Results suggest that the soil fertility decreases quickly if soil is exposed for long periods and no organic matter or fertilizer is applied; conversely grass may maintain and improve soil productivity. Results also indicate that hill slope cultivation and erosion caused the topsoil, nutrients and organic matter to accumulate down slope.