Adding nutrients to agricultural systems is essential to enhance crop yield, crop quality, and economic returns. Commercial fertilizers are typically used to supply needed nutrients to crops. Nitrogen (N), phosphorus (P), and potassium (K) fertilizers are used extensively. Other secondary and micronutrient fertilizers are generally required in small quantities to correct plant nutrient deficiencies.

An Amish farmer uses a horse team to spread fertilizer on a field in Lancaster County, Pennsylvania.

Commercial fertilizers contain a guaranteed quantity of nutrients, expressed as fertilizer grade on a label showing the weight percentage of available N, P₂ O₅, and K₂ O equivalent (N-P-K) in the fertilizer. Additional nutrients in fertilizer formulations are listed at the end of the fertilizer grade with the nutrient identified. Commonly used commercial fertilizers include ammonium nitrate (fertilizer grade 33-0-0), urea (45-0-0), urea-ammonium nitrate (28-0-0), anhydrous ammonia (82-0-0), diammonium phosphate (18-46-0), monoammonium...