translation.en: We stopped planting clover and alfalfa, which are natural fertilizers that fix nitrogen in the soil, and instead we started using synthetic fertilizers.
translation.zh: 我们停止种植三叶草和苜蓿， 它们是天然的肥料，可以固定土壤里游离氮， 然而，我们开始使用人工肥料。