This kind of grass can't be seen in any place but in the place that the soil is rich.

=This kind of grass can be seen not in any place but in the place that the soil is rich.

可以看出这是not A but B结构，否定A，肯定B。A、B分别为状语，所以用where引导地点状语从句。

另一种分析方法：

将but分析为介词，意为除了，= except。除了土地肥沃的地方。

where为融合型关系词，= (in/at/to) the place where/that/in which 即等于先行词+定语从句.

所以可以用where取代in the place that.

in which只能引导定语从句，前面并没有先行词，所以为错误。