To analyze the relationship between the feature 'PH' and the task of predicting the grain yield of the soybean cultivar as either 'low' or 'high', we need to consider the typical pH values that are indicative of these target classes.

Based on prior knowledge, pH is a measure of the acidity or alkalinity of a substance, and for soybean cultivars, the pH of the soil can significantly affect the grain yield. Generally, soybeans prefer a slightly acidic to neutral pH range.

Considering a range of 1 to 4 for the feature 'PH', we can make the following assumptions for the typical pH values:

- Target class 'low': pH values between 3.8 and 4.2 are relatively low for soybeans and may indicate lower grain yield potential.
- Target class 'high': pH values between 5.5 and 6.0 are relatively high for soybeans and may indicate higher grain yield potential.

Based on these assumptions, here is the dictionary with the typical pH values for each target class:

```json
{
	"low": [3.8, 3.9, 4.0, 4.1, 4.2],
	"high": [5.5, 5.6, 5.7, 5.8, 5.9]
}
```

Please note that these values are assumed based on general knowledge and may vary depending on specific conditions and factors.