Based on prior knowledge, the feature 'PH' can be related to the grain yield of the soybean cultivar. However, to determine the appropriate ranges of values, additional context or domain knowledge is needed. 

Assuming that the pH range for soil suitability for soybean cultivation is typically between 5.5 and 7.5, we can assign the following target classes based on the pH value:

- "low" (pH < 5.5): Low grain yield
- "high" (pH >= 5.5): High grain yield

To generate the dictionary with the given format, I will provide 5 typical pH values for each target class:

```json
{
	"low": [4.8, 4.9, 5.0, 5.3, 5.4],
	"high": [5.6, 5.8, 6.2, 6.7, 7.0]
}
```

Please note that these typical pH values are just assumptions and may vary depending on specific conditions or scientific studies in the field of soybean cultivation.