Based on prior knowledge, the relationship between the Season feature and the grain yield of a soybean cultivar can be analyzed as follows:

In general, the grain yield of soybean cultivars tends to be higher during specific seasons, while lower during others. The exact seasons vary depending on factors like the climate and growing conditions, but typically there are certain seasons that are more favorable for high grain yields.

To create the dictionary with specific details, let's assume that the feature values for Season are integers ranging from 1 to 2.

Based on this analysis, here is the dictionary with typical Season values for each target class:

```json
{
	"low": [1.0, 1.0, 1.0, 1.0, 1.0],  
	"high": [2.0, 2.0, 2.0, 2.0, 2.0]  
}
```

Please note that the values in the dictionary are examples based on the assumption that 1 represents a season associated with low grain yield, while 2 represents a season associated with high grain yield. The actual values for each target class may vary depending on the specific dataset and analysis.