Based on my prior knowledge and understanding of soybean cultivation, the number of grains per plant (NGL) is a crucial feature that directly affects the grain yield of soybean cultivars. A higher value of NGL indicates a greater number of grains per plant, which generally leads to a higher grain yield. Conversely, a lower value of NGL suggests a lower number of grains per plant, which typically results in a lower grain yield.

To create the dictionary with the feature values for each target class, we can assign typical values of NGL for 'low' and 'high' grain yield as follows:

```json
{
	"low": [50.0, 55.0, 60.0, 65.0, 70.0],
	"high": [90.0, 95.0, 100.0, 105.0, 110.0]
}
```

These values are just examples and can be adjusted based on the specific context and prior knowledge about soybean cultivation.