Based on prior knowledge, the PH feature is a measure of soil acidity or alkalinity. Soil pH values range from 1 to 14, where 1 represents highly acidic soil, 7 represents neutral soil, and 14 represents highly alkaline soil.

To determine the ranges of values for the PH feature that correspond to low and high grain yield of the soybean cultivar, we need additional information or data. Without this information, it is not possible to reliably determine the specific ranges of PH values that will result in low or high grain yield.

However, assuming a general relationship between soil pH and soybean yield, we can make some speculative assumptions:

- Low grain yield may occur at both extremely acidic (1-4) and extremely alkaline (10-14) soil pH values.
- High grain yield may occur in the moderately acidic (5-6) to moderately alkaline (8-9) soil pH range.

Although these assumptions are not based on specific information about soybean cultivars, they provide a starting point for the analysis.

Based on these assumptions, the dictionary can be formed as follows:

```json
{
	"low": [1.0, 2.0, 3.0, 4.0, 10.0],  
	"high": [5.5, 5.6, 8.5, 8.6, 9.5]
}
```

Please note that the values provided are just examples to demonstrate the format of the dictionary and may not accurately represent the actual relationship between soil pH and soybean yield for a specific cultivar. To obtain more accurate and reliable information, it is advised to consult relevant research studies or conduct experiments specifically designed to analyze the relationship between soil pH and the grain yield of the soybean cultivar of interest.