Based on my prior knowledge and analysis, the Number of legumes per plant (NGP) can be an important factor in determining the grain yield of a soybean cultivar. A higher NGP generally indicates a higher yield, while a lower NGP indicates a lower yield.

Here is a dictionary outlining the possible values of NGP for each target class:

```json
{
	"low": [2.0, 1.5, 1.8, 2.2, 2.4],  
	"high": [3.5, 4.0, 3.2, 3.8, 4.2]
}
```

In the "low" target class, typical NGP values could range from 1.5 to 2.4, while in the "high" target class, typical NGP values could range from 3.2 to 4.2. Please note that these values are just examples and may vary depending on the specific characteristics of the soybean cultivar and the farming conditions.