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Manure Nutrient Losses
Manure Nutrient Losses
Manure nutrients are lost during manure handling, storage, treatment, and application. Manure nitrogen is especially vulnerable to volatilization when ammonium is transformed to ammonia. Losses of phosphorus and potassium are primarily due to runoff and erosion.
Losses from storage and treatment facilities
Nutrient losses vary with types of manure storage and treatment facilities. Losses of manure phosphorus and potassium are minimal with some manure handling systems, but considerable phosphorus and potassium may be lost from open feedlots to runoff and leaching. Manure nitrogen losses are relatively higher in open feedlots and with poultry manure on shavings or sawdust, and relatively less with bottom- loaded slurry storage and pits under slatted floors.
Anaerobic treatment of manure results in considerable loss of nitrogen, mostly in the form of ammonia due to volatilization. During anaerobic digestion of manure, organic matter in the liquid decomposes and is emitted as methane gas and carbon dioxide. Much of the particulate matter, including phosphorus and potassium compounds, settles to the bottom. Some of the liquid with low nutrient and organic matter content is regularly removed to maintain the storage capacity of the lagoon while the sludge is left to accumulate at the bottom of the lagoon. The phosphorus and potassium in anaerobic lagoons is potentially recoverable by removing the sludge, but this generally is not done more than once every 15-25 years to avoid interruption of the anaerobic decomposition process.
Composting accelerates the decomposition of organic matter, yielding a less bulky and more stable organic product. A significant amount of ammonium is lost during composting as ammonia is either released to the atmosphere or inorganic nitrogen is tied-up in stable organic compounds.
Ammonium available following application
When manure is not incorporated, significant nitrogen losses can occur following land application due to volatilization of ammonia. This is especially true for liquid effluents, which have greater concentrations of the total nitrogen in ammonium form. If manure is immediately incorporated, little or no ammonium is lost, but 100 percent can be lost without incorporation. On hot and windy days, 100 percent of the ammonium can be lost within two days following surface application.
Nitrogen Availability Factors for Manure
Manure Nutrients - Crop Available or Pollutant?
Mineralization of nutrients and crop availability
Plants take up nutrients in inorganic forms. Ammonium and nitrate in manures are immediately available to crops. Organic material needs to decompose to allow mineralization of nutrients to inorganic forms that plants can use. Manure type affects the rate of mineralization, often due to differing carbon:nitrogen ratios. Poultry manure typically has a low carbon:nitrogen ratio compared to cattle or swine manure, and has a high rate of mineralization. Litter or bedding in manure will slow decomposition and mineralization of the nutrients. Nutrients in anaerobically-treated manure will mineralize relatively quickly. Incorporated manure will decompose faster than if left on the soil surface.
A major part of organic nitrogen is not available in the season of application. About 25 percent of organic nitrogen in solid manure from beef feedlots is typically available in the year of application (see availability factors above). Organic nitrogen continues to be mineralized in subsequent years, releasing approximately 12 percent and 5 percent of the organic nitrogen applied in the second and third years, respectively, after application. Mineralization of nitrogen from compost is slow as the composting process results in the formation of stable organic compounds that resist decomposition.
Much of the manure phosphorus is in dissolved inorganic forms and crop available until phosphorus ions are fixed by calcium or iron (in most Nebraska soils). Calcium and iron phosphate are only slowly available to plants.
Crop removal of nutrients
Removal of nutrients by grain and forage crops is related to yield. Harvest of 200-bushel corn removes approximately 140 pounds nitrogen, 60 pounds P2O5 and 40 pounds of K2O. Alfalfa and soybean can derive much of their nitrogen from the atmosphere.
Biological nitrogen fixation is inhibited when soil nitrogen levels are high and the crops will obtain a major part of the required nitrogen from the soil. Alfalfa is able to capture nitrate which has leached beyond the rooting zone of annual crops.