Based on prior knowledge and common understanding, the number of stems (NLP) can potentially have an impact on the grain yield of soybean cultivars. A higher number of stems may indicate greater branching and potentially higher grain yield, whereas a lower number of stems may suggest lower branching and lower grain yield.

To generate the dictionary, we need to analyze the relationship between the NLP feature and the task. Without any specific data, we can only provide general assumptions. Here's a possible dictionary based on these assumptions:

```json
{
	"low": [2.5, 3.0, 3.5, 4.0, 4.5],  
	"high": [5.0, 5.5, 6.0, 6.5, 7.0]
}
```

Please note that the values provided are just hypothetical and may not reflect the actual range of NLP values for the given task. It is crucial to analyze actual data or consult domain experts for more accurate insights.