Based on prior knowledge and experience, the Number of grains per pod (NS) is typically positively correlated with grain yield in soybean cultivars. A higher NS value indicates a higher grain yield, while a lower NS value indicates a lower grain yield.

To create the dictionary, let's consider some typical NS values for the 'low' and 'high' target classes:

For 'low' target class (low grain yield):
- Typical NS values: [1.0, 1.5, 1.8, 2.2, 2.5]

For 'high' target class (high grain yield):
- Typical NS values: [3.0, 3.2, 3.5, 3.8, 4.0]

Based on this analysis, the dictionary can be formulated as follows:

```json
{
	"low": [1.0, 1.5, 1.8, 2.2, 2.5],
	"high": [3.0, 3.2, 3.5, 3.8, 4.0]
}
```