Based on prior knowledge, the pH levels can affect the grain yield of soybean cultivars. Typically, a pH range of 6.0 to 7.5 is considered favorable for soybean growth. Below 6.0 or above 7.5, the soybean crop can exhibit stunted growth and lower grain yield.

To analyze the relationship between the feature "PH" and the target of grain yield, we can consider the following:

- Low grain yield: pH levels below 6.0 or above 7.5
- High grain yield: pH levels within the range of 6.0 to 7.5

Based on this analysis, here is the dictionary with specific PH values for each target class:

```json
{
	"low": [5.5, 5.7, 5.9, 7.8, 8.2],
	"high": [6.2, 6.4, 6.6, 7.2, 7.4]
}
```

Please note that the provided PH values are just examples and may vary depending on specific conditions and research findings.