ASSIMILATION VS. ACCUMULATION OF MACRO- AND MICRO-NUTRIENTS IN SOILS: RELATIONS TO LIVESTOCK FEEDING OPERATIONS

Authors: Cole, Noel; Schwartz, Robert; Todd, Richard

Submitted to: American Society of Animal Science Annual Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/1/2004
Publication Date: 7/26/2004
Citation: Cole, N.A., Schwartz, R.C., Todd, R.W. 2004. Assimilation vs. accumulation of macro- and micro-nutrients in soils: relations to livestock feeding operations. Extension Workshop held at the American Society of Animal Science Annual Meeting, July 26, 2004, St. Louis, Missouri. p. 36-51

Interpretive Summary: Nutrient management is an integral part of profitable agrisystems, but in some areas of the U.S. continued inputs of fertilizer and manure nutrients in excess of crop requirements have led to a buildup of nutrient concentrations that are of environmental concern. Proper use of nutrients in livestock manures is becoming more critical for sustainability of concentrated animal feeding operations (CAFO) because new environmental regulations require that nutrients be properly applied and managed. Most agronomic soil tests were developed to determine appropriate inorganic fertilizer application rates and must be used with caution when determining manure application rates. Losses of nutrients such as nitrogen (N) and phosphorus (P) can be reduced by refining the rations fed, increasing nutrient retention by livestock, moving manures from areas of surplus to deficiency, finding alternative uses for manure, using cropping and haying systems that remove excess nutrients, and using conservation practices such as limited tillage, buffer strips and cover crops to limit runoff and leaching. Whole farm nutrient balances are useful for educating producers about quantities of nutrients being managed and the flow of nutrients, but they can also be misleading because of spatial factors such as uneven nutrient application that introduce environmental risk not noted with a whole-farm nutrient balance. Manure utilization plans also need to deal with nutrients that potentially leave the field or production area in route to sensitive ecosystems on or near the production unit.

Technical Abstract: Amending soils with animal manures is a common practice to increase soil fertility while disposing of potential wastes from concentrated animal feeding operations (CAFO). However, improper application of manure can result in runoff of nutrients or pathogens to surface waters, percolation of nutrients to ground water, accumulation of nutrients in the soil, or loss of significant quantities of N and C to the atmosphere. The trend toward larger animal feeding operations has resulted in higher rates of manure and litter application in localized areas; thus, increasing the potential for pollution from land applied manure. With the advent of the new clean water regulations all CAFO and many smaller animal feeding operations must have comprehensive nutrient management plans that are designed for proper utilization of manure nutrients. Unfortunately, only 20 to 50% of CAFO have adequate land to meet land application standards. The nutrient composition and phytoavailability of CAFO manures vary greatly. The capacity of soils to bind or accumulate nutrients varies with soil type, previous management/fertilization, and tillage method. In some cases, nutrients can accumulate in soils to the point of being toxic to plants. Application of manures to pastures is normally not sustainable because less than 20% of the nutrients applied ever leave the field in animal tissues or products. However, when the forage is cut for hay or silage, appreciable quantities of applied nutrients can be exported. Areas adjacent to CAFO can receive appreciable quantities of nitrogen via dry or wet deposition. These can be advantageous to some crops or forages, but may be detrimental to plants sensitive to nutrient inputs such as native range or forests. Speciation data indicate that the relatively nontoxic dietary organic form of arsenic can be converted to the more toxic form in soils, suggesting that continuous land application of arsenic-containing poultry litter could potentially be detrimental to long-term soil and water quality. For optimal sustainability, fertilization levels need to be balanced with plant requirements. However, even under the best management systems some accumulation or escape of nutrients is inevitable. Therefore, nutrient management plans must recognize the need to deal with nutrients that accumulate in soils or leave the field or production area.