Based on my prior knowledge, the thousand seed weight (MHG) can be a significant factor in determining the yield of soybean cultivars. Usually, a higher thousand seed weight indicates a higher yield potential. However, without further data or research, it is challenging to determine specific value ranges for the "low" or "high" categories.

To complete the analysis, I will assume some typical MHG values and categorize them as either "low" or "high" yield based on general knowledge.

Here is the analysis and dictionary for the given feature:

```json
{
	"low": [21.5, 22.0, 22.5, 23.0, 23.5],
	"high": [25.0, 25.5, 26.0, 26.5, 27.0]
}
```

Please note that the values provided are just approximations and may not represent the actual thresholds for "low" and "high" grain yields. additional research or data would be needed to establish more accurate ranges.