No, don't do it!...... the nutes have to be diluted by pre mixing with water before application to soil....trying to get the correct dilution relying upon rainfall is a big mistake....IMHO! The undiluted ferts are way too concentrated for the plants roots to handle...they'll be fried!
edit
^^^why not just collect rain water and mix nutes in then pour on plants?
(excerpted from above)
That would work fine!