Qualifications
"Biosystems engineer" is less a job description and more of a collegiate focus. So, if you want to work in biosystems engineering, you should major in biosystems engineering—but put the brakes on printing those "biosystems engineer" business cards. Funny the way that works.
How do you become a biosystems engineering major in the first place? Take all of your school's chemistry, biology, and physics classes, and then realize that, meh, even though you're a math genius, they just don't interest you. Then take your school's environmental science class, and realize that, hey, maybe you do want to be an engineer.
During college, most biosystems engineering majors take a common core curriculum with dual emphasis on ecological engineering and bioprocess engineering. We're talking all things "bio:" biofuels, biomaterials, biography—er, wait. Maybe not that last one.
The tricky part is becoming a biosystems engineer with a specialty. You're the all-purpose flour of the engineering world. Everyone wants your sort of specific-but-still-incredibly-broad brand of general skills. It's your responsibility to figure out what kind of cookie you want to become.
Resource conservation? Great, intern with the U.S. Forest Service. Have a passion for gardening equipment? You can do that, too. Love food engineering? Hit General Mills with that beautiful résumé of yours.
If you can't think of an application for all the skills you've learned in school, then you're probably not the creative, problem-solving person that biosystems engineers should be.