求分析下句 还有 of which 可以用that 替换么 为什么

半截句子 看不懂
出处
Natural foods,for example,are vegetables,fruit and grain which have been grown in soil that is rich in organic matter.In simple words,this means that the soil has been nourished(给…营养) by unused vegetable matter,which provides it with vitamins and minerals.This in itself is a natural process compared with the use of chemicals and fertilizers,the main purpose of which is to increase the amount—but not the quality—of foods grown in commercial farming area.
与使用农药和化肥的相比,这本身是一个自然成长过程,这样做的主要目的是提高商业种植区农作物产品的数量而不是质量.
这里的which 指代前面的整个句子
不可以用 that 替换