Recent precipitation has got me concerned about the excessive water going into places it should not be. Ponds and lagoons have the tendency to overfill and excess water can take a toll in ditches and retention walls. Our large dairy operations have strict regulations to respond to rainy days just as the ones we had before. According to Texas A&M Extension publications, dairies, swine operations, beef cattle feedlots, and poultry houses generate substantial amounts of manure. This by-product is an excellent source of nutrients that can be used to feed plants. The manure also adds organic matter to soil that improves its nutrient retention, water-holding capacity, infiltration, and porosity. When properly managed, manure can be a valuable resource. Research demonstrates that advanced manure application techniques that incorporate manure into the soil are superior to traditional surface application in terms of retaining nitrogen and reducing negative environmental impacts. These advanced methods vary in their ability to reduce nitrogen loss from ammonia volatilization, nitrate runoff and leaching, and nitrous oxide emissions. Therefore, farmers must consider cost, nutrient efficiency, and environmental risks when choosing an application method. Understanding the nitrogen cycle and environmental impacts is essential to choosing application techniques that are most compatible with specific manure characteristics, land use and cropping regimes, and farm management practices. Animals convert a portion of feed nitrogen into milk and meat protein; the remainder is excreted in urine and feces as organic and inorganic nitrogen. This manure is treated/stored, then applied to crop or forage land, where the nitrogen (as urea and organic nitrogen compounds) undergoes various chemical transformations. Manure application: Nitrogen is excreted in livestock and poultry urine as urea (in mammals) or uric acid (in birds), and as urea, ammonia, and organic nitrogen (proteins, organic acids, and amino acids) in feces. Urea hydrolysis: Hydrolysis of urea by urease (produced by microorganisms in feces and soil) converts urea into ammonia, ammonium, and carbon dioxide gas. Soil pH greater than seven favors ammonia volatilization and enhances this process. Ammonia volatilization: This process is the conversion of liquid ammonium into ammonia gas that is lost to the atmosphere. High soil pH and temperature favor ammonium to ammonia conversion. Losses are greatest when this conversion occurs at the soil surface when manure is spread and not incorporated into the soil immediately. Nitrification: Ammonium has a positive charge that binds it to negatively charged clay particles that can be taken up by plant roots. Under aerobic conditions (oxygen present) nitrifying bacteria in the soil converts ammonium to nitrite and then to nitrate in a few days or weeks. In process, nitrous oxide and nitric oxide gases are lost to the atmosphere. Nitrate is highly soluble and plants take it up more rapidly than ammonium–ammonium is bound to clay particles in the soil where roots must reach it. Denitrification: The process by which soil bacteria convert nitrate and nitrite into gaseous nitrous oxide and nitric oxide, and eventually to nitrogen gas, which are lost to the atmosphere. This process occurs under anaerobic conditions (e.g., oxygen-poor soils due to water logging).
Leaching: Nitrate is leached mainly during rainy seasons and fallow periods, when percolating rainfall washes it from the plant root zone. Immobilization: This process occurs when soil organisms take up nitrate and ammonium and temporarily lock up the nitrogen. When these organisms die, the organic nitrogen in their cells is mineralized into ammonium, which is again available to plants. Mineralization: This process is the reverse of immobilization. Microbes in the soil convert organic nitrogen from manure and organic matter to ammonium. The rate of mineralization increases with soil temperature, moisture, and oxygen. Applying large quantities of manure without a proper nutrient management plan can damage soil, water, and air quality. Ammonia, nitrate, and nitrous oxide are the nitrogen compounds that pose the greatest concern for human health and the environment. Nitrous oxide and methane, which emit from stored manure, are potent greenhouse gases. Advanced manure application techniques vary in how well they minimize ammonia volatilization, increase crop nitrogen uptake, improve forage and crop quality, and reduce emission of nitrous oxide. These measures differ according to manure consistency and nutrient loading, application rate, timing of application, weather conditions, land cover and topography, soil structure and moisture content. All of these manure application techniques, particularly for slurry manure, reduce ammonia and nitrous oxide emissions compared to conventional surface application methods. For more information on this or any other agricultural topic please contact me at [email protected] or call the Hopkins County Extension Office at 903-885-3443.
