Cow manure, depending on bedding amounts, weighs in at a dismal 0.5% nitrogen, 0.5% phosphorus, and 0.5% potassium, low in all three elements. Be sure to cure cow manure by giving it plenty of time in your compost pile. Horse manure usually scores slightly better in all categories with a 1.5–1.0–1.5 N-P-K rating and a shorter composting time.