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MANURE AND NUTRIENT MANAGEMENT 399 11 Manure and Nutrient Management Concern about the impact of nutrient loadings on the environment, that is, the relation of livestock and poultry manure to groundwater contamination, is well- documented both inside the United States (Brown et al., 1989; Frink, 1969; Harris, 1987; Lanyon and Beegle, 1989; Madison et al., 1986; Patni and Culley, 1989; Pinkowski et al., 1985; University of Wisconsin-Extension and Wisconsin Department of Agriculture, Trade and Consumer Protection, 1989; U.S. Congress, Office of Technology Assessment, 1990; Walter et al., 1987; Young et al., 1985) and outside the United States (Adams and McAllister, 1975; Phillips et al., 1982; Steenvoorden, 1986; Webster and Goulding, 1989). RESOURCE UTILIZATION OR WASTE DISPOSAL A little more than 50 years ago, animal manures were considered a tremendous asset in providing fertility to U.S. soils. The 1938 yearbook of agriculture stated: One billion tons of manure, the annual product of livestock on American farms, is capable of producing $3,000,000,000 worth of increase in crops. The potential value of this agricultural resource is three times that of the Nation's wheat crop and equivalent to $440 for each of the country's 6,800,000 farm operators. The crop nutrients it contains would cost more than six times as much as was expended for commercial fertilizers in 1936. Its organic matter content is double the amount of soil humus annually destroyed in growing the Nation's grain and cotton crops (U.S. Department of Agriculture, 1938:445).
MANURE AND NUTRIENT MANAGEMENT 400 Today, animal excrements are largely referred to as wastes for disposal rather than as manures for utilization. The change in attitude toward manure has mainly been a result of two factors. First, livestock and poultry production has become concentrated in large-scale, confinement-type enterprises. These include dairy cow operations with hundreds of cows, beef and hog feedlots with thousands of animals, and poultry enterprises with many hundreds of thousands of birds. In 1987, for example, only 7.5 percent of all beef cow-calf producers had herds larger than 100 animals, but these producers produced 47.6 percent of all the calves produced. In 1990, cattle feedlots with capacities of 1,000 head or more represented only 4 percent of the total feedlots, but they fed 84 percent of the cattle that year (Krause, 1992). Such large concentrations of animals or birds have greatly magnified the problems related to handling of wastes, including hazards to human health and aesthetic nuisances. Second, marked improvements in the techniques for making fertilizer from atmospheric nitrogen were made in the period before World War II. During the war, the federal government built numerous plants for the manufacture of fixed nitrogen for munitions. At the war's end, these manufacturing plants became available for making farm fertilizers at relatively low prices. Equally spectacular achievements have been realized in the production of highly effective phosphorus fertilizers from rock phosphates. Benefits of Manure Application Even though fertilizer prices have increased considerably in recent years as a result of increasing energy costs, in many instances they remain lower than the cost of handling animal manures. Therefore, if one looks only at the economic value of manure as a source of plant nutrients, particularly nitrogen, the use of manure may not be competitive. There are other benefits, however, from using animal manures in crop production systems. Continuous and judicious use of manure improves the physical and chemical properties of nearly all soils, particularly those that are shallow, coarse textured, or low in organic matter; and the potential for degradation of the quality of soil, air, and water resources is greatly reduced. More specifically, manure provides essential elements for crop growth. It adds organic matter, it improves soil structure and tilth, and it increases the soil's ability to hold water and nutrients as well as resist compaction and crusting (Madison et al., 1986). The return of nutrients and organic matter to the soil by manure completes the ancient and natural cycle on which all life depends. Soil fertilityâthe ability of soil to provide nutrients for plant growthâis enhanced by such judicious returns of nutrients. The composition of
MANURE AND NUTRIENT MANAGEMENT 401 manures, however, depends on the kind of animal or bird, the type of feed, storage and handling procedures, climate, and other factors. Nonetheless, soil chemical properties are generally improved by animal manures, unless the manures are added in excess. Supply of Manure The American Society of Agricultural Engineers (1988) has established standard values for estimating the amounts and compositions of manures produced in the United States (Table 11-1). Cross and Byers (1990) used these values together with recent livestock and poultry statistics to estimate the total amount of manure and the economic value of the nutrients in manure produced in the United States (Table 11-2). Beef cattle in extensive (grazing) production systems contribute about seven-eighths of the total beef cattle manure, whereas beef cattle on feed contribute only about one-eighth. For dairy cattle manure, as much as one-half or two-thirds might be voided on pastures, although the trend TABLE 11-1 Manure and Its Associated Nutrient Content Millions of Metric Tons (dry weight) Source Total Manure Nitrogen Phosphorus Potassium Cross and Byers (1990) 143 5.9 1.8 3.7 Van Dyne and Gilbertson 102 3.7 0.9 2.2 (1978) Committee on Long-Range 124 5.1 1.4 NR Soil and Water Quality (1993; this report) NOTE: NR, no data reported. TABLE 11-2 Economic Value of Nitrogen, Phosphorus, and Potassium in Manures Total Manure Nutrient Value (millions of dollars) (millions of metric tons) Source Nitrogen Phosphorus Potassium Cross and Byers 143 1,611 668 895 (1990) Van Dyne and 102 1,016 334 524 Gilbertson (1978) Committee on Long- 124 1,387 498 NR Range Soil and Water Quality (1993; this report) NOTE: NR, no data reported.
MANURE AND NUTRIENT MANAGEMENT 402 to intensive (confinement) production systems is expected to continue. Essentially all poultry are produced in confinement. For intensive animal production systems, the predominant sources of voided manure in terms of solids and nitrogen appear to be dairy cattle, swine, beef cattle, broilers, turkeys, and laying hens. Van Dyne and Gilbertson (1978) also estimated the amount of manure and nutrients contained in manure produced by livestock and poultry in 3,050 counties in the United States. Their estimates, 102 million, 3.7 million, 0.9 million, and 2.2 million metric tons (112 million, 4.1 million, 1 million, and 2.4 million tons) of manure, nitrogen, phosphorus, and potassium, respectively, on a dry-weight basis, were somewhat lower; but in most regards they were similar to the estimates of Cross and Byers (1990) given in Table 11-1. Van Dyne and Gilbertson (1978) also estimated that losses caused by volatilization, leaching, and runoff would reduce the dry weight by 10 percent, total nitrogen by 36 percent, phosphorus by 5 percent, and potassium by 4 percent. Of the 102 million metric tons (112 million tons) of dry manure produced, Van Dyne and Gilbertson (1978) estimated that 47 million metric tons (52 million tons) was economically recoverable. The committee also estimated manure and nutrients produced by livestock and poultry as one element of estimated nitrogen (see Chapter 6) and phosphorus (see Chapter 7) mass balances (see the Appendix for a complete discussion of the methods used to estimate manure production) for each state and for the United States as a whole. The economic value of the nutrients available in manure shows the benefits that can be attained by using manure as a resource. Manure as Waste The concentration and specialization of modern crop and livestock production systems has led to a breakdown of manure recycling as it occurred on livestock and crop farms in the past (Walter et al., 1987). Figure 11-1 shows the break in the livestock-crop nutrient cycle. Synthetic fertilizers replace manures as a nutrient source, and manure becomes a waste problem. Often, the least-cost solution to the manure waste problem is to apply it to the land (Walter et al., 1987). Simply disposing of manure as a waste product can lead to serious degradation of both surface water and groundwater. Likely sources of surface water and groundwater contamination include runoffs and leaching from manure and wastewater applied to the land, open and unpaved feedlots, runoff holding ponds, manure treatment and storage lagoons, and manure stockpiles. Dead animal disposal and animal
MANURE AND NUTRIENT MANAGEMENT 403 dipping vats may contribute to surface water and groundwater contamination. Manure accumulations around livestock watering locations, intermittent-use stock pens, and livestock grazing operations that occur on areas ranging from sparsely grazed rangelands to intensively grazed pastures may also influence surface water and groundwater quality (U.S. Congress, Office of Technology Assessment, 1990). FIGURE 11-1 Schematic of livestock-crop system showing gap in traditional manure recycling system because of use of relatively inexpensive fertilizers. Source: M. F. Walter, T. L. Richard, P. D. Robillard, and R. Muck. 1987. Manure management with conservation tillage. Pp. 253â270 in Effects of Conservation Tillage on Groundwater Quality: Nitrates and Pesticides, T. J. Logan, J. M. Davidson, J. L. Baker, and M. R. Overcash, eds. Chelsea, Mich.: Lewis Publishers, a subsidiary of CRC Press, Boca Raton, Florida. With permission. The presence of constituents such as pathogenic organisms, nitrate, and ammonia in livestock drinking water may adversely affect livestock health (U.S. Congress, Office of Technology Assessment, 1990). The presence of the same constituents in surface water or groundwater drink water supplies may adversely affect human health. Consequently, effective on-farm nutrient management is essential. IMPROVING MANURE MANAGEMENT Technologies are available to improve manure management, and wider use of these technologies could reduce the water pollution caused by misuse of manures. Producers trying to improve the ways that they
MANURE AND NUTRIENT MANAGEMENT 404 manage manures face particularly difficult problems that need to be overcome before new technologies can be successfully applied. Special Problems in Manure Management Improvements in manure management can effectively capture the benefits of using manures as inputs to crop production systems and can reduce the water pollution associated with manure disposal. Special problems with the management of manures as production inputs must be overcome if manure management is to be improved. These problems include handling and application costs, estimating nutrient value, determining the amount of manure to be applied, balancing multiple nitrogen and phosphorus applications, concentration of livestock, and the need for storage and handling facilities. Handling and Application Costs High labor requirements for manure handling, the increased travel distances required to spread manure, and reduced opportunities for using manure as a resource on-farms have tended to increase the cost of using manure as a nutrient source. Investigators have developed management systems that reduce the amount of labor required to handle manure and that increase its nutrient value. These systems, however, require significant capital investments for the construction of storage and handling facilities and the purchase of application equipment. These capital costs can be an important constraint to the adoption of these systems. Difficulty Estimating Nutrient Value of Manures Nitrogen is often the plant nutrient that first becomes limiting in crop production systems. Much of the nitrogen in manure is in organic form and must be mineralized before it can be used by plants. In contrast to nitrogen, the phosphorus in manures is generally conceded to be as effective as acid-treated forms of inorganic phosphorus, such as superphosphate (a common formulation used in commercial phosphorus fertilizers) (Azevedo and Stout, 1974). Potassium in manure is also considered readily available. Direct losses of nitrogen, phosphorus, and potassium via volatilization, leaching, and runoff are estimated to reduce the nutrient content of manure significantly. The nutrient contents of different manures can vary significantly, making estimation of application rates difficult. Furthermore, not all nutrients in manure
MANURE AND NUTRIENT MANAGEMENT 405 are immediately available for crop growth. Improved storage, treatment, and application equipment can reduce these manure utilization problems. The uncertainty in estimating the quantity and availability of nutrients in manures can lead to their overapplication or to the use of supplemental nutrient sources when none are required for crop growth. Manure testing services to estimate the nutrient content of manures are available, however, and should be used to improve manure management. Reduced Need for Manure after Repeated Applications Gilbertson and colleagues (1979) developed a technical guide (Table 11-3) that estimates the amount of manure that must be added to supply 112 kg of available nitrogen per hectare (100 lb/acre). This guide is based on the principles that the percentage of nitrogen in manure that is released in the first year increases with the amount of nitrogen in the manure and that it takes 3 or more years before most of the nitrogen present in manure is mineralized and available to plants. The important point is that when manure is applied to the same field year after year, each succeeding year requires less manure to maintain a supply of 112 kg of plant-available nitrogen per hectare (100 lb/acre). TABLE 11-3 Quantity of Livestock or Poultry Manure Needed to Supply 100 kg of Nitrogen over the Cropping Year with Repeated Applications of Manure Quantity (metric tons) Needed for Manures with the Following Percent Nitrogen Number of Years 0.25 1.0 2.0 4.0 Applied 1 154.1 22.2 7.0 1.4 2 79.3 15.6 5.8 1.4 3 53.8 12.7 5.1 1.4 4 40.9 11.0 4.7 1.3 5 33.0 9.8 4.4 1.3 10 17.0 6.9 3.7 1.3 15 11.5 5.6 3.3 1.2 20 8.7 4.8 3.0 1.2 SOURCE: Derived from J. S. Schepers and R. H. Fox. 1989. Estimation of N budgets for crops. Pp. 221-246 in Nitrogen Management and Ground Water Protection, R. F. Follet, ed. Developments in Agricultural and Managed-Forest Ecology 21. Amsterdam: Elsevier.
MANURE AND NUTRIENT MANAGEMENT 406 Nitrogen-Phosphorus Trade-Off The ratio of nitrogen to phosphorus in fresh manure is generally 3 or 4. Since a significant amount of nitrogen is lost by volatilization, the nitrogen:phosphorus ratio of manure applied to the land is often less than 3. Therefore, when manure is applied at rates sufficient to supply adequate nitrogen for most cropping conditions, excess amounts of phosphorus and potassium are added. For example, Sharpley and colleagues (1984) found that 8 years of continuous manure usage resulted in large accumulations of available phosphorus. Christie (1987) also found significant increases in extractable phosphorus in soil that had been treated with cow or pig manure slurries. The increased phosphorus contents of surface soil increase the potential for soluble and sediment-bound phosphorus to be transported in runoff and, therefore, has water quality implications, as discussed in Chapter 7. Sharpley and Smith (1989) recently developed an equation that predicts the soluble phosphorus concentration of runoff on the basis of the available phosphorus of the surface soil determined by a soil test. Van Reimsdijk and colleagues (1987) also warned that spreading of animal manure on land in quantities exceeding the amount of phosphorus taken up by plants results in phosphorus accumulation. They stated that when the cumulative excess becomes large compared with the buffering capacity of the soil, phosphorus could leach to surface water and groundwater, causing eutrophication. (Eutrophication is the process by which a body of water becomes âeither naturally or by pollutionârich in dissolved nutrients such as phosphates and, often, becomes seasonally deficient in dissolved oxygen.) They concluded, however, that these negative effects develop only after a relatively long period of large manure applications and that soils differ widely in their buffering capacities. The potential phosphorus buildup from the use of manure poses a tremendous challenge for managing animal wastes. Historically, manure application rates have mainly been based on nitrogen loading rates, with little attention paid to phosphorus accumulation. However, with the growing environmental concern associated with phosphorus in surface water supplies, pressures are mounting for limiting or even banning phosphorus additions to soils that exceed a certain level of plant-available phosphorus on the basis of a soil test. Such criteria could result in significantly reduced manure application rates or even no manure applications. Michigan recently adopted guidelines indicating that manure additions should be restricted to rates adequate to replace the phosphorus removed by crops once the available phosphorus level determined by a soil test reaches a value of 160.
MANURE AND NUTRIENT MANAGEMENT 407 The use of phosphorus as the criterion for determining manure loading rates may be appropriate, particularly in regions containing surface waters where accelerated eutrophication can occur. In other areas, however, the benefits derived from using manures to enhance overall soil quality and as the primary source of nitrogen for supplementing plant growth may outweigh any potential negative effects associated with increased phosphorus levels. Therefore, risk assessments for specific regions rather than adoption of generic standards across regions should be made. Concentration of Livestock The concentration of livestock production in large confinement feeding operations or regional concentrations of dairy, poultry, or other animal production systems has resulted in situations in which there is simply more manure being produced than can be used efficiently on nearby croplands. Nutrient flows in intensive livestock operations are directly related to outputs as animals and animal products. In contrast to the situation on cash grain farms, the proportion of nutrient input that exits in product output is usually much less for intensive livestock operations. This accumulation causes a net nutrient loading on the farm that may exceed the crop's nutrient needs (Lanyon and Beegle, 1989) and degrade water quality. According to Young and colleagues (1985), southeastern Pennsylvania, and Lancaster County in particular, are among the most intensively farmed areas in the United States. In Lancaster County, between 1960 and 1986, beef cattle numbers increased by 55 percent, dairy cattle increased by 61 percent, hogs increased by 677 percent, poultry layers and pullets increased by 193 percent, and broilers increased by 504 percent (Lanyon and Beegle, 1989). This production intensity is linked to continuing development pressures on agricultural land coupled with excellent marketing conditions, in that one-third of all U.S. consumers live within 124 km (200 miles) of Lancaster County. This situation threatens local and regional environments because southeastern Pennsylvania agricultural land is a major source of the nutrients and pesticides that enter the Chesapeake Bay (Young et al., 1985). The volume of manure produced in areas where livestock production is concentrated may well exceed the area of cropland available on which to apply manures at rates that minimize the potential for surface water or groundwater degradation. For example, 0.9 metric ton (1 ton) of solid dairy cattle manure contains approximately 4.5 kg (10 lb) of
MANURE AND NUTRIENT MANAGEMENT 408 nitrogen, 2.3 kg (5 lb) of phosphate (P2O5), and 4.5 kg (10 lb) of potash (K2O) (Madison et al., 1986). If a 635-kg (1,400-lb) dairy cow, for example, produces 50 to 57 kg (110 to 125 lb) of manure and bedding daily, a 50-cow herd will produce about 454 metric tons (500 tons) of manure daily. At a maximum application rate of 56 metric tons/ha (25 tons/acre), 8 ha (20 acres) of cropland is required. Additional lands may be required to spread manure from calves, heifers, steers, or other livestock (Madison et al., 1986). Figure 11-2 illustrates the problem of manure production and land application. FIGURE 11-2 Ratio of amount of manure produced to amount of cropland available for manure application. Source: U.S. Department of Agriculture, Soil Conservation Service, 1989. Water Quality Indicator Guides: Surface Waters. Report No. SCS-TP-161. Washington, D.C.: U.S. Department of Agriculture. Van Dyne and Gilbertson (1978) also estimated the ratio of manure production to land area in the United States. The average ratio of economically recoverable manure weight to cropland area and improved pasture averaged only 0.27 metric tons of manure per hectare (0.12 tons/acre) nationally across all 3,050 counties of the United States. The range was from less than 0.02 metric dry tons/ha (0.01 dry tons/acre) to a high of 4.0 metric dry tons/ha (1.8 dry tons/acre). Although there is adequate cropland in all areas of the United States to receive manure, it is often not in the immediate vicinity of the animal manure source or under the control of the livestock producer. As a result, these facilities often stockpile wastes or apply it to
MANURE AND NUTRIENT MANAGEMENT 409 croplands at rates in excess of those required for maintaining soil quality. Figure 11-3 shows manure production and nitrogen concentration (on an as- voided basis) within various intensive animal production systems versus extensive livestock production systems as a function of animal density and spacing per unit live weight (U.S. Congress, Office of Technology Assessment, 1990). FIGURE 11-3 Average amount of manure nitrogen produced by animals per unit area in relation to animal spacing. Source: Adapted from U.S. Congress, Office of Technology Assessment. 1990. Technologies to improve nutrient and pest management. Pp. 81-167 in Beneath the Bottom Line: Agricultural Approaches to Reduce Agrichemical Contamination of Groundwater. Report No. OTA-F-418. Washington, D.C.: U.S. Government Printing Office.
MANURE AND NUTRIENT MANAGEMENT 410 Storage and Handling Facilities Off-site utilization of manures is constrained because of the high costs associated with the facts that both semisolid and liquid manures are bulky material to handle, the use of manure in an environmentally acceptable manner limits the application time period, and sufficient hauling equipment must be available during the limited application time period (the equipment then goes unused for the remainder of the year) (Young et al., 1985). Although some manure transactions occur now, there is not a flourishing market for manure, and the potential for marketing excess manure nutrients with a positive return to farmers is limited. Considering the volume of the excess manure on-farms in southeastern Pennsylvania, Young and colleagues (1985) concluded there is no reason to anticipate improved circumstances for manure marketing with positive returns to farmers. The trend of increasing farm animal numbers adds to the dilemma. Manure that is collectible is concentrated geographically. Gilbertson and colleagues (1979) mapped areas where manure from livestock and poultry can be collected and spread economically. There appear to be three geographic areas of special interest: (1) New York, Pennsylvania, and Vermont; (2) Wisconsin, Iowa, southern Minnesota, northern Illinois, eastern South Dakota, and eastern Nebraska; and (3) southern California and New Mexico (Walter et al., 1987). Opportunities for Improvement For management purposes, animal wastes can be divided into point and nonpoint sources. Point sources, such as feedlots and other confinement facilities, are regulated by the U.S. Environmental Protection Agency (EPA). Point source animal waste management problems must be addressed in terms of existing situations as well as expanding and new facilities. It is essential that environmentally sound waste management plans be developed during the planning of all new and expanding confinement feeding operations. Improving existing facilities to meet regulatory standards presents a greater challenge. Nonpoint sources of livestock manure are characterized by diffuse runoff from areas such as feeding and watering sites. In most cases, these sites are not regulated, do not produce collectable manure, and are manageable through proper site selection away from streams, soil erosion control, cover cropping, and use of vegetative filters to minimize transport of potential contaminants to streams (Sweeten, 1991). Manure-fertilized
MANURE AND NUTRIENT MANAGEMENT 411 pastures and croplands are also regarded as nonpoint sources of nitrogen and phosphorus pollution. With the increased national concern about the effects of nonpoint sources of pollution on water quality, increasing attention will be given to how and when animal wastes are applied to pastures and croplands and at what rates. Nutrient management plans, tailored for local conditions, are essential for safeguarding the soil and water resources over the long-term. Using a flush-clean system, cattle manure is washed from the confinement area to underground concrete tanks. After screening, the manure wash will be pumped onto fields with irrigation water. Credit: Agricultural Research Service, USDA. Point Source Control The initial concern with confinement feeding operations was fish kills associated with the runoff that enters streams and lakes. Therefore, regulations and policies focused on controlling runoffs from those operations that were considered point sources. Technologies or best-management practices for water quality protection from concentrated animal feeding operations have been well developed and are widely implemented (Sweeten, 1991). These point sources are directly regulated by the EPA and/or state agencies, with the basic requirement of no discharge, that is, containment and proper
MANURE AND NUTRIENT MANAGEMENT 412 disposal of all manure, wastewater, and runoff for up to 25 years and for a 24- hour-duration storm event. For purposes of water pollution control, intensive livestock production systems are defined by EPA regulations for feedlots as animal feeding operations [where animals are] stabled or confined and fed or maintained for a total of 45 days or more in any 2-month period, and â¦ crops, vegetation, forage growth or post- harvest residues are not sustained in the normal growing season over any portion of the lot or facility (U.S. Environmental Protection Agency, 1976:11,460, as cited by U.S. Congress, Office of Technology Assessment, 1990). This definition covers many animal species, types of facilities, animal densities, climates, and soils. It uses a single, visually determined criterionâ that is, the absence of vegetation. Under such conditions, manure production and animal traffic are of sufficient quantity and duration to prevent germination or growth of forage. This condition implies that runoff, volatilization, and leaching pathways may be proportionately larger from unvegetated surfaces than from vegetated surfaces (U.S. Congress, Office of Technology Assessment, 1990). Consequently, the U.S. Congress, Office of Technology Assessment (1990) has concluded that EPA regulations for confined livestock and poultry operations deal with surface water protection and do not include requirements for groundwater protection. Several states and local entities do have groundwater protection requirements. For example, the Texas Water Commission regulation that governs confined, concentrated livestock and poultry feeding operations includes groundwater protection for lagoons and holding ponds. The regulation requires that all wastewater retention facilities be constructed of compacted, low-permeability soils (for example, a clay or clay loam) at a minimum thickness of 30 cm (12 inches) (U.S. Congress, Office of Technology Assessment, 1990). Sweeten (1991) lists the following best-management practices as appropriate for achieving a no-discharge system: â¢ proper site selection; â¢ selection of appropriate types of facilities with respect to climate, topography, geology, soils, land resource base, land use, and proximity to surface water or groundwater or neighbors; â¢ reduced sizes of open feedlots, diversion of runoff outside the feedlot, covered manure storage facilities, and installation of roof gutters on feedlot buildings; â¢ use of frequent dry scraping, debris basins, or screen separators;
MANURE AND NUTRIENT MANAGEMENT 413 â¢ use of lagoons, holding ponds, or storage tanks or pits for liquid manure and/or runoff; â¢ sealing or lining of earthen storage and treatment structures for groundwater protection, subject to permeability testing; â¢ adequate systems for manure and wastewater distribution on croplands or pasturelands; â¢ dead animal disposal in clay-lined dry pits or by composting and utilization; and â¢ land application at rates consistent with crop production and water quality goals. Nonpoint Source Control Control of nonpoint sources of animal wastes requires improvements in manure management in smaller and diverse livestock operations. Effective manure management strategies have been determined (University of Wisconsin- Extension and Wisconsin Department of Agriculture, Trade and Consumer Protection, 1989) and should include the following: â¢ awareness of the nutrient value of manure; â¢ manure analysis; â¢ proper crediting of nutrients; â¢ appropriate application methods, rates, and timing; â¢ site considerations; â¢ manure storage; â¢ effective and efficient disposal of animal wastes; and â¢ designated cattle lanes and fencing. Although some technologies and best-management practices address all of these objectives, additional efforts are needed to promote the development and adoption of such practices. Of major importance is the need to develop and extend economic guidance for land application of manures, including soil and manure testing to define appropriate application rates and information about nutrient release rates to allow efficient and economically viable use of manures. These efforts must include quantification of the magnitude of nutrient losses from lagoons, storage tanks, and land application as a function of design, operation, and climatic variables to develop nutrient management plans and nutrient mass balance models. Increases in the agronomic uses of manure might be fostered through joint efforts among states, cities, industry, and agriculture to promote manure processing and use on public and private lands. Development
MANURE AND NUTRIENT MANAGEMENT 414 of incentives for manure use in cropping systems, particularly in areas with high levels of manure production, may offer an opportunity to enhance the agronomic use of this resource as opposed to treating it as a waste disposal problem. Federal and state programs that include cost-sharing or other economic incentives that encourage livestock producers to adopt and implement water quality protection practices, particularly in areas where water is most vulnerable, could promote the adoption of such incentives. Technical assistance (provided by the Soil Conservation Service of the U.S. Department of Agriculture [USDA]), education (provided by the Cooperative Extension Service of USDA), and research (supported by the Agricultural Research Service of USDA) must be able to promote and support the adoption of water quality protection practices by producers. For example, demonstration livestock production operations in areas with high or low pollution potentials for groundwater could serve to disseminate information on appropriate best- management practices that contain provisions for groundwater protection (U.S. Congress, Office of Technology Assessment, 1990). Efforts to increase the adoption of improved manure management practices may face important economic and social obstacles. The effects of on-farm nutrient loss abatement practices on farm income may be great. Moderate nutrient loss reductions may be achieved with negligible effects on-farm profits. Substantial reductions in nutrient losses, however, could have significant effects. Without taxpayer assistance, measures to reduce nutrient losses significantly could impose financial hardships on producers (Young et al., 1985). The economic farm model of Young and colleagues (1985) determined that nutrient losses could be reduced about 10 percent with negligible impacts on net farm economic returns by using manure storage, the more even application of manure on croplands, and changes in the intensity of crop rotation. Given the fact, however, that the additional income generated by adding a cow exceeds the additional expenses associated with disposing of the extra manure when society bears the pollution impact, overapplication of manure nutrients is economically rational (Young et al., 1985). Facilitating change in management techniques can be a slow process. The rate of adoption of various practices is a function of many factors (Harris, 1987). Knowing that nutrient losses from farms must be reduced to achieve water quality improvements and that achieving such reductions is technically feasible is only the first step toward a sound nutrient management program. Social and economic information will be needed to determine what kinds of implementation policies are needed to obtain nutrient reductions in targeted watersheds in an efficient and equitable
MANURE AND NUTRIENT MANAGEMENT 415 manner while giving due consideration to the taxpayers and the heritage of the area. These issues can be resolved only with additional social and economic research to complement and augment ongoing agronomic, biological, and hydrologic research (Young et al., 1985). Alternative Uses of Manure There may be some promise of developing alternative products from animal manures. Livestock and poultry manures generated from concentrated and confined animal feeding facilities may be valuable sources of fertilizer, feedstuff, or fuel. Manure is widely used as an organic fertilizer in many areas. Certain types of manure also may receive limited use in specialized situations as animal feedstuffs, as a substrate for anaerobic digestion to produce methane gas, or as a fuel for combustion or gasification for electric power generation. These alternatives are not without problems. Some alternative uses return all or part of the original manure fertilizer value as a residue that eventually is applied to land. Power generation requires economies of scale for it to be profitable, and refeeding of manure causes livestock health problems if it is done at high levels. Preliminary evaluations of these alternatives indicate that they would be expensive to implement at a scale sufficient to solve the excess nutrient problems in Lancaster County, for example. Moreover, care should be taken when evaluating alternatives for off-site manure disposal subsidized by public funds. Reducing manure disposal costs merely makes animal production more profitable. Thus, farmers are encouraged to expand their operations, further aggravating the problem. Animal numbers should not be increased unless the manure can be used in an environmentally acceptable manner (Young et al., 1985). Alternative useful products can be produced from manure, and these products can be exported from the producing farm. However, increased development of manure management treatment and use technologies, particularly in relation to composting, methane gas generation, thermochemical conversion, fiber recovery, and marketing of such products, will be required to take advantage of these opportunities.
MANURE AND NUTRIENT MANAGEMENT 416