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

经济作物种植地区的主要的目的是增加作物的产量而不是质量
你说的应该是定语从句里的：of which 不可以用that替换，因为of which等同于when/where/why这种类型的。
stage purpose 等先行词在定语从句中作状语时可用where
与that相同的是which

of which中的which指代use of chemicals and fertilizers，而use of chemicals and fertilizers与purpose是逻辑上的从属关系，所以要说purpose of which, 就象要说purpose of use of chemicals and fertilizers一样，所以就不能用that替换。

NO.不可以