Based on prior knowledge, the Season feature is likely to have an influence on the grain yield of soybean cultivar. The value of Season represents different seasons in which the soybean is grown. 

To analyze the relationship between Season and the grain yield, we can start by looking at historical data or studies that have been conducted on soybean cultivars. By examining the data, we can identify typical values of Season for low and high grain yield.

Once we have the data, we can create a dictionary with the appropriate format. Here is an example:

```json
{
    "low": [1.2, 1.0, 0.9, 0.8, 1.5],
    "high": [2.5, 2.3, 2.7, 2.2, 2.1]
}
```

In this example, we assume that the season values for low grain yield are typically less than 1.5, while the season values for high grain yield are typically greater than 2.0. The specific values provided in the dictionary are just hypothetical examples.

Please note that in order to provide a more accurate analysis, it is important to have access to actual data or research related to soybean cultivars and their grain yield based on the seasons.