COMPOSTER & linzelu100,
If you are interested in nutrient density, here is a link to a website that I regularly visit. They have a lot of good information for building healthy soils and strong plants that can increase yields and nutrient density. They've helped me to understand that nitrogen isn't the most important factor in growing more prolific vegetables. This site is also linked to High Brix Gardens which is a very informative and useful site.
http://www.aglabs.com/
http://www.highbrixgardens.com/
dpurdy