http://www.amazon.com/The-Intelligent-Gardener-Growing-Nutrient/dp/0865717184
http://www.amazon.com/Building-Soils-Naturally-Phil-Nauta/dp/1601730330
http://www.amazon.com/Science-Agriculture-Advanced-Methods-Sustainable/dp/0911311351
http://www.amazon.com/Teaming-Nutrients-Gardeners-Optimizing-Nutrition/dp/1604693142
http://www.amazon.com/Neal-Kinseys-Hands-On-Agronomy-Kinsey/dp/0911311599
http://www.acresusa.com/the-biological-farmer