Why Are Manure and Fertilizer Used in Fields?

What You Need to Know

Every plant that grows in a field absorbs nutrients from the soil. When that plant is harvested and removed from the field, those nutrients leave with it. A single acre of corn, for example, removes approximately 160 pounds of nitrogen, 60 pounds of phosphorus, and 50 pounds of potassium from the soil each year. Without replenishment, the soil's nutrient reserves become exhausted within a few seasons, and crop yields collapse.

This is why farmers have applied manure and fertilizer for thousands of years. The two serve complementary purposes.

Manure is animal waste, typically from cattle, poultry, hogs, or horses. Its benefits extend beyond simple nutrient content. Manure adds organic matter to soil, which improves soil structure by creating aggregates that allow air and water to penetrate. It increases the soil's water-holding capacity, critical during dry periods. It feeds earthworms and beneficial soil microorganisms that break down organic matter and make nutrients available to plants. And it supplies a broad spectrum of macro and micronutrients in slow-release form.

However, manure alone has limitations. Its nutrient content is variable and relatively low compared to synthetic fertilizer. A ton of dairy cow manure contains roughly 10 pounds of nitrogen, 5 pounds of phosphorus, and 10 pounds of potassium. To supply a corn crop's nitrogen needs from manure alone would require approximately 16 tons per acre, which creates logistical and environmental challenges.

Synthetic fertilizer addresses these limitations. Products like urea (46-0-0), DAP (18-46-0), and muriate of potash (0-0-60) deliver precise quantities of specific nutrients in concentrated form. A farmer can calculate exactly how much nitrogen, phosphorus, and potassium a crop needs based on soil tests and yield goals, then apply the exact amount required. Synthetic fertilizer is also more practical to transport, store, and apply uniformly across large fields.

Modern agriculture typically uses both. Manure provides the organic matter and biological benefits that synthetic fertilizer cannot, while synthetic fertilizer fine-tunes the nutrient supply to match crop demands precisely. This integrated approach maintains soil health while achieving the yields needed to feed a growing population.

Without either input, continuous cropping would deplete soil fertility within 3 to 5 years, and yields would drop to a fraction of their potential. The practice of fertilizing fields is the foundation of productive agriculture worldwide.