Based on prior knowledge, the number of stems (NLP) is an important factor for the grain yield of soybean cultivars. Typically, a higher number of stems would result in a higher grain yield.

Here is the dictionary with possible values of feature NLP for the target class 'low' and 'high':

```json
{
	"low": [0.0, 1.0, 2.0, 3.0, 4.0],  
	"high": [10.0, 12.0, 15.0, 18.0, 20.0]  
}
```

Please note that these values are just examples and should be adjusted based on the specific context and knowledge of the problem at hand.