If you can demonstrate than your machine does work on different soils or under quite different conditions, potential buyers/users might be more inclined to use or buy your machine.

It's very necessary in order to give good manufacturer's recommendations

Yes, if you want to sell or recommended it for other soils than it is required. Further following conditions should also be tested-

1. Different levels of water in field such as 15 cm. 30 cm, 40 cm etc.

2. Gender basis trial - may not suit both sexes

3. Height of seedlings.

4. Type of nursery - Mat/broadcasting normally

Wish you all the best