Manure and commercial fertilizers supply major nutrients such as nitrogen, phosphorus and potassium to growing plants. However, before 1950, when World War II bomb factories were converted to fertilizer production facilities, organic manure was the only option for growers.
Nutrients from organic manure are not immediately beneficial to plants because the organic matter must first be broken down by microorganisms in the soil. On the other hand, commercial fertilizers are fast-acting and provide quick nutritional boosts to developing plants. Organic manure also helps to enhance to soil structure, increasing the soil's ability to hold onto nutrients more effectively than if using commercial fertilizer.
Primary sources of organic manure include poultry, dairy and beef cattle, swine, sheep, horse and guano, whereas commercial fertilizers are manufactured from nonliving materials. Content of commercially manufactured fertilizers is listed on the packaging as a ratio of the three macronutrients (nitrogen, phosphorus and potassium), whereas manure samples must be analyzed to provide the same information.
If used as instructed, organic manure offers several long-term environmental benefits over commercial fertilizer. Organic manure will increase soil carbon levels and decrease soil erosion and runoff, as well as nitrate leaching.