You certainly can’t believe everything you read on the internet, but there is wealth of information out there. “Land grant universities” that have schools of agriculture still do a good amount of research and service to the public, and many have online databases of free publications (often in PDF format) available.
Here in Illinois, the University of Illinois has some good ones. They’re not all available in PDF unfortunately, but you certainly print them to PDF for your records. The main publication search page for UI is Vista, but the following free books caught my eye –
The University of California – Davis also has a whole host of publications online. The Free Publications page is great to browse, but here are some of my favorites –
The National Sustainable Agriculture Information Service (ATTRA) also has a huge publications list and for obscure and highly specialized but interesting newsletters and magazines, you should check out the AgZines page of the US Agricultural Information Network. And don’t forget free Google e-books – most of the free ones are old out-of-print publications, but you can find some real gems under Gardening if you have the time and inclination to browse.