Once the humus layer disappears, nutrients cannot be recycled and leach from the soil, converting soil from fertile to infertile and making it suitable only for savanna vegetation.

一旦腐殖质层消失，养分就无法从土壤中回收和过滤，致使土壤由肥沃变为贫瘠，只适于热带草原植被的生长。

youdao

It was found that the humus layer in black soil region was thick in north and thin in south, which was due to the climatic condition and soil-forming process.

研究发现，深厚黑土主要分布于黑土区北部，中厚与薄层黑土则分别集中在黑土区的中部和南部，这主要与黑土分布区的气候条件和黑土的成土过程有关。

youdao

Porter, and he volunteered seventy acres of land where he had grown only cotton or corn for twenty-eight years, applied no fertilizer, and almost completely depleted the humus layer.

NEWYORKER: Testing, Testing