theory of humus mutrition

例句：

1. 1. The soil is rich in humus, which makes it suitable for growing vegetables.
   土壤富含腐殖质，非常适合种植蔬菜。
2. 2. The farmer used to till the land with a hoe, but now he relies on the natural humus of the soil.
   这位农民过去用锄头翻地，但现在依赖土壤的自然腐殖质。
3. 3. The forest floor is covered in a layer of humus, which helps to retain moisture and nurture plants.
   森林地面覆盖着一层腐殖质，有助于保持水分并滋养植物。