Based on the given feature "PH" and the task of predicting the grain yield of a soybean cultivar as low or high, we need to analyze the relationship between the feature and the target.

Analysis:
The feature "PH" refers to the pH level of the soil. Soil pH is a crucial factor that impacts plant growth and productivity. Generally, soybean plants prefer slightly acidic to neutral pH levels in the range of 6 to 7.5. pH levels below 6 or above 7.5 may adversely affect soybean growth and yield.

Based on this prior knowledge, we can assume the following ranges of values for the feature "PH" to be appropriate for determining the grain yield as low or high:

- Low yield: pH levels outside the preferred range of 6 to 7.5, i.e., values below 6 or above 7.5.
- High yield: pH levels within the preferred range of 6 to 7.5.

Now, let's create a dictionary with possible values of the feature "PH" for each target class:

```json
{
	"low": [5.0, 5.5, 5.8, 7.8, 8.2],  
	"high": [6.0, 6.5, 7.0, 7.2, 7.4] 
}
```

In the "low" class, the selected pH values are below the preferred range, including values like 5.0, 5.5, 5.8, 7.8, and 8.2.
In the "high" class, the chosen pH values are within the preferred range, including values like 6.0, 6.5, 7.0, 7.2, and 7.4.

Please note that these values are for demonstrative purposes and actual experiments or domain knowledge should be utilized to determine the relationship between the "PH" feature and the target variable accurately.