Soil Fertility & Plant Nutrition

Nutrient Deficiencies and Toxicities of Plants: American Phytopathological Society Press; This reference can be ordered on-line.; "This book discusses the role of essential nutrients in relation to nearly two dozen crops. Use the book's 307 color photographs to diagnose disorders in the field. The accompanying text explains symptoms in detail, with information provided by 31 crop experts. Covers the following crops/crop groups: peanuts, corn, rice, sorghum, wheat and other small grains, sugarcane, sugar beet, soybeans, cotton, cucurbits, onions, tomato, common bean, potato, apples and pears, citrus, peaches and nectarines, grapes, and turfgrass."

PKalc: International Plant Nutrition Institute; The spreadsheet PKalc v1.13 is an interactive tool that allows you to keep track of historical nutrient additions and removals for a field or field area.

Nonconventional Soil Additives: Products, Companies, Ingredients, and Claims

Iowa State Soil Fertility Web Site: Includes a photo gallery of nutrient deficiency symptoms.