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Wind and spring floods erode soils , exposing underlying layers and premiering new compositions of humus and minerals on the surface .

风沙和水灾侵蚀着土壤，暴露出地下土层，腐殖质新成分及其表面的矿物。

Soil microorganism plays an important role in the process of nutrient transformation and humus forming in soil .

土壤微生物在土壤养分转化与腐殖质形成过程中有著重要的作用。

Soil which contains a lot of humus is more fertile than that which only has a little .

富含腐殖质的土壤比只含有少量腐殖质的土壤要肥沃多了。

So the topsoil is bits of rock mixed with things that are once alive . These things in the topsoil that were once alive are called humus .

可见，土壤是石粒和曾经是活体的物质的混合物。表土中这种曾是活体的东西叫做“腐殖质”。

Plants grow in soil which has a dark colour . This dark soil is humus .

植物生长在黑色的土壤里，这种黑色土壤叫腐殖上。