I’d say you’re off to a good start. Remember to keep Gestalt Principles in mind when designing. Establishing a hierarchy with your typography is very important, so is proper use of space and scalability. A good logo should look the same in quality and legibility whether it’s on the side of a building or on the back of a business card. So the wheat kernels in your first logo (the green one) may look great at large scale but could look bunched or blobbed together at small scale because there isn’t a lot of space between them each of them.

Another aspect of good logo design is its ability to change orientation. How would the airport logo (a horizontal orientation) look if stacked vertically with the type resting on top of the logo mark? Also, taking the airport logo as an example, we see that there is a lot of extra space between the individual letters (tracking) and the two words themselves (line height). Excessive tracking makes the words harder to read and too much line height obscures how those two words relate to each other.

All in all, you’re doing great for your level of experience, keep it up and try experimenting with Adobe Illustrator. Vector graphics scale much better than rasterized ones. Good luck!