Based on prior knowledge and experience, the number of grains per plant (NGL) is expected to have a positive correlation with grain yield. Hence, higher values of NGL are likely to indicate a higher grain yield, while lower values may signify a lower grain yield.

To generate a dictionary with typical NGL values for low and high grain yield, we can assume the following ranges based on general knowledge of soybean cultivation:

- For low grain yield (low):
    - Typical NGL values: [10.0, 15.0, 20.0, 25.0, 30.0]

- For high grain yield (high):
    - Typical NGL values: [40.0, 45.0, 50.0, 55.0, 60.0]

Hence, the dictionary representation would be:

```json
{
	"low": [10.0, 15.0, 20.0, 25.0, 30.0],
	"high": [40.0, 45.0, 50.0, 55.0, 60.0]
}
```