当我们挖掘土壤时,会发现表层土壤颜色发暗,发灰,甚至发黑,而表层以下土壤颜色则变成棕色、黄色或红色。这是为什么呢?这是由于在表层土壤中含有机物质的缘故。土壤有机质是土壤的重要组成部分。它在土壤中的含量并不 When we excavate the soil, we find that the surface soil is dark, gray and even black, while the soil below the surface turns brown, yellow or red. This is why? This is due to the organic matter in the surface soil. Soil organic matter is an important part of the soil. Its content in the soil is not