Based on my prior knowledge, I will analyze the relationship between the feature PH and the task of predicting the grain yield of a soybean cultivar as either low or high.

Analysis:
PH is a measure of soil acidity or alkalinity, and it can affect the growth and yield of plants. In the case of soybean cultivars, the appropriate range of PH values may vary, but typically, a PH range of 5.5 to 7.0 is considered suitable for soybean growth and high yield. PH values below 5.5 or above 7.0 may indicate soil conditions that are not optimal for soybean cultivation, potentially resulting in lower grain yield.

Based on this analysis, let's create a dictionary detailing the possible values of the feature PH for each target class:

```json
{
	"low": [4.5, 4.8, 5.1, 5.3, 5.4],
	"high": [6.8, 6.9, 7.1, 7.3, 7.6]
}
```

Note: The values presented in the dictionary are just examples and not exhaustive. They represent typical PH values for each target class, with 'low' representing lower grain yield and 'high' representing higher grain yield.