Nutrient Management On Pastures.

Nutrient management on pastures is a critical part of maintaining and improving their ability to provide key ecosystem services including forage and fuel production, clean air and water, and climate mitigation. Our objective was to determine the scientific underpinning for purported benefits of nutrient management on pastures. We searched the peer-reviewed literature addressing nutrient inputs to pastures and practices designed to retain nutrients in the pasture, but limited our searches to U.S. pastures used for grazing or haying, explicitly excluding rangeland. We found that that nearly 500 million tons of manure is applied to U.S. pastures either through direct deposition by grazing animals or land application of stored manure. Nutrient additions also come in the form of inorganic fertilizers applied to pastures at highly variable rates and times. Nutrient management involves the development of a nutrient budget for sources and placement methods that accounts for plant requirements, soil supply, and nutrient losses from the system. Of particular importance is the difference in nutrient budgets between hayed and grazed pastures because grazing animals return a large portion of ingested forage nutrients to the soil through their excreta, which increases the rate of nutrient cycling. Many environmental and management factors combine to determine the fate of nutrients applied to pastures. An important part of nutrient retention is maintaining or improving the physical, chemical, and biological capacity of the soil for productivity by building soil organic matter. Both gaseous and aqueous losses of nutrients from pastures are often lower than that from row crops because pasture vegetation is typically more dense and perennial. However, when pastures receive high nutrient inputs and/or are managed such that significant bare soil is exposed, nutrient losses can be quite high, adversely impacting water and air quality at local, regional, and global levels.