Based on prior knowledge, the feature PH (soil pH) can potentially have a relationship with grain yield of soybean cultivars. However, without more information or domain-specific knowledge, it is challenging to determine the appropriate ranges of soil pH values.

Assuming that lower soil pH values indicate acidic conditions and higher values indicate alkaline conditions, we can speculate the following relationship between soil pH and grain yield:

1. Low Grain Yield: Typically, soybean cultivars may have lower yields in both highly acidic (pH < 5) and highly alkaline (pH > 8) soils. We can consider values in the range of 4 to 5.5 as potential low pH values.

2. High Grain Yield: Soybean cultivars generally prefer slightly acidic to neutral soil conditions (pH 5.5 to 7). However, it is important to note that the optimal pH range for maximum grain yield can vary depending on the specific cultivar and environmental conditions.

Based on this analysis, we can create a dictionary with typical PH values for each target class:

```json
{
    "low": [4.0, 4.5, 5.0, 5.5, 6.0],
	"high": [5.5, 6.0, 6.5, 7.0, 7.5]
}
```

Please note that these values are purely speculative and may vary in reality. It is always advisable to consult specialized knowledge, domain experts, or experimental data for more accurate relationships between features and target variables.