Based on prior knowledge, we can analyze the relationship between the feature "Number of grains per plant" (NGL) and the task of determining the grain yield of a soybean cultivar as either low or high.

Analysis:
In general, a higher number of grains per plant would likely result in a higher grain yield, indicating a high target class. Conversely, a lower number of grains per plant would suggest a lower grain yield, representing a low target class. However, the specific ranges for low and high NGL values may vary depending on the specific characteristics of the soybean cultivar and other factors such as environmental conditions, genetics, and management practices.

Based on this analysis, we can create a dictionary with typical NGL values for each target class:

```json
{
	"low": [10.5, 12.8, 11.2, 9.7, 10.9],
	"high": [15.6, 16.2, 17.9, 14.3, 15.8]
}
```

Please note that these values are just examples and may not accurately represent the ranges for all soybean cultivars. It is recommended to consult specific research or expert knowledge for a more accurate analysis.