1989 - 1994
The Effects of Livestock Manure Application
D. King1, G.C. Watson2
, G.J. Wall1, and B.A. Grant2
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Livestock production is an important agricultural industry in Ontario accounting for approximately 54% of farm cash receipts (approx. $3.1 billion) in 1991. The Agricultural Statistics for Ontario (1991) reported approximately 3 million swine, 0.7 million dairy cattle, 1.6 million beef cattle, and 28.4 million poultry. The disposal of the animal wastes generated by this industry can represent both a valuable agronomic resource and, potentially, an environmental liability. This study has focused on the disposal of liquid swine manure on soils managed under conservation tillage systems and examined the potential for the contamination of surface waters and methods of reducing that contamination.
The concern for the contamination of surface water by nitrogen and bacteria constituents found in manure arises from their threat to human health and wildlife habitat. Nitrate-N concerns are related primarily to infant health and in particular methaemoglobinaemia (infant cyanosis or blue baby) (Fraser and Chilvers, 1981). In recognition of this problem a safe limit of 10 mg NO3-N L-1has been established for drinking water (OME, 1992). While the evidence is less direct, nitrate and nitrite-N have also been linked with cancer by reactions leading to the formation of nitrosamines (Fraser et al. 1980). While nitrosamines are known to be very active carcinogens in animals, there is no direct evidence linking them to human cancer. A third potential drinking water health effect from nitrates, relates to malformations of the central nervous system and musculoskeletal system in infants (Dorsch et al. 1984). In addition, because nitrates are a concern for livestock health a provincial water quality guideline limit on livestock drinking water concentrations of 20 mg NO3-N L-1 has been recommended for farm use.
Concentrations of ammonium in water is also a concern for wildlife populations with fish, for example, being highly sensitive to free NH3 in water. Toxic to chronic toxicity concentrations of un-ionized ammonia for rainbow trout have been reported of 0.02 to 0.16 mg L-1 respectively (Thurston et al. 1984; Thurston and Russo 1983). By comparison, ammonium concentrations of up to 5 mg L-1 may be associated with manure spills while Spires and Miller (1978) report mean surface water runoff concentrations of 1.8 mg L-1 from manured fields.
The concentrations of bacterial populations in manure are such that any inputs to surface or subsurface water supplies may result in levels of contamination in the water in excess of water quality guidelines for Ontario. Ontario water quality bacteria standards for drinking and recreational use are 0 and 100 counts per 100 mL respectively of Escherichia coliform (E.coli.) and fecal coliform (OME, 1992).
The trends toward liquid manure handling systems and conservation tillage systems in Ontario have raised questions regarding the best manure management methods to achieve maximum economic yield while preventing nitrogen and bacterial contamination of tile drains and groundwater. Liquid manure application methods, application rates for different soils and crops, and the timing of application are among questions being asked by producers.
Beauchamp and Kachanoski (1990) have suggested that conservation tillage practices should work well with manure injection systems by conserving nitrogen and reducing nutrient runoff losses. In addition, chisel plowing after manure application should result in sufficient crop residues left on the soil surface to prevent significant runoff of nutrients. However, incorporation of manure into no-till cropping systems remains a problem. The authors cite a Quebec study that found when manure was used as a source of nitrogen in a no-till corn crop, poorer corn seedling emergence, weed control and an increased risk of frost damage occurred. In addition, the formation of macropores by earthworms, which is enhanced by a reduction in tillage, can increase the likelihood of manure contaminants reaching the tile drains. Research has indicated that while conventional injection methods may be effective in reducing odours and losses of ammonia to the air they may result in levels of tile water contamination equal to or greater than surface broadcasting methods (Fleming and Bradshaw, 1992).
While it is frequently assumed that bacteria are not transported great distances through the soil matrix, recent studies have suggested that bacterial transport through soil macropores may be a significant process in contamination of tile drainage waters. Patni et al. (1984) reported an increase of fecal bacteria populations in tile drain water minutes to hours after irrigation with liquid manure. In tile drains with an average depth of 75 cm Culley and Phillips (1982) observed high fecal bacteria counts for several days following fall or winter application of liquid manure. Recent studies by Dean and Foran (1991) in southwestern Ontario have further increased concerns with respect to direct transport of bacteria to tile drains from liquid manure applications. In their field studies they observed that tile drains became contaminated with fecal coliform shortly after liquid manure application for 9 of 12 events monitored. In these studies, tillage of the soils prior to manure application appeared to disrupt macropore continuity and prevent bacteria transport to the tile drains.
The role of macropores in the transport of surface applied nutrients is not yet well understood and is of particular concern for no-till fields where agricultural amendments are usually applied to the soil surface and macropore systems are not subjected to periodic disruption by tillage (Shipitalo et al. 1990). The lack of disturbance or disruption by tillage, which is associated with no-till systems, has also been shown to result in increased earthworm activity that can significantly contribute to macropore formation (Beven and Germann 1982; Edwards et al. 1988). The phenomenon of preferential flow by macropores acts to conduct water and solutes quickly to significant soil depths without the soil matrix being saturated (Beven and Germann, 1982; Thomas and Phillips, 1979). Measurement has been limited of the magnitude of nutrient losses by preferential flow in unsaturated soil and accompanying solute transport variability from a field scale under no-till management.
In a joint effort between Agriculture and Agri-Food Canada, the Upper Thames River Conservation Authority, the Ontario Ministry of Agriculture Food and Rural Affairs, and the Ontario Ministry of the Environment and Energy this study was conducted with the following objectives:
Surface water runoff collected from microplots indicated the modified injection method under NT management significantly reduced nutrient and bacteria contamination compared to other conventional treatments. The loadings of nutrients and bacteria which were observed in the subsurface tile water may pose an environmental concern. The field scale study suggested liquid manure application on medium textured soils under NT tillage systems can result in excessive levels of nutrient and bacterial contamination in the tile drain waters. The observation of manure contaminants in tile drain waters shortly after manure application suggests downward movement by preferential flow. Disturbance of macropores by cultivation (eg. modified injection method) prior to liquid manure injection in NT fields can reduce the levels of contamination in surface runoff and tile drain waters compared to surface applied and conventional injection methods. The negligible differences in fuel consumption between the injection methods tested indicates that the modified injection method is also an economically viable alternative for farmers. The loss of nutrients to tile drains from liquid manure applied at a rate equivalent to crop production nitrogen requirements is relatively low from a crop production standpoint.
5. NEW TECHNOLOGIES AND BENEFITS
The prototype manure injection system tested in this study was designed to disrupt soil pore continuity in reduced and no tillage systems while maintaining surface residues. As previously discussed, soil macropores or preferential flow can contribute significant quantities of nutrients and bacteria contaminants to tile drains which may pose an environmental concern. The reduction of macropores near the soil surface prior to the application of manure could therefore allow farmers using no-till systems to apply manure to those fields. The prototype liquid manure injection system was effective in sidedressing manure between corn rows at the six-leaf stage of corn growth which will allow farmers to supplement the nutrient requirements of the crop and improve the utilization of manures as a nutrient resource.
The system used for monitoring flow in tile drains proved to be an inexpensive and reliable method of monitoring flow rates continually over an extended period of time. The method may have applications for other research activities where the monitoring of water flows at relatively low rates (0 to 10 litres min-1) is required.
6. IMPLICATIONS FOR THE GREAT LAKES BASIN ECOSYSTEM:
The potential for contamination of surface waters by surface runoff and tile drainage contributions from the application of liquid manure to agricultural fields has been clearly identified. Results of this study have indicated that while conventional injection methods of manure application are effective in reducing surface runoff losses, they continue to contribute equal or greater levels of manure contaminants to the tile drains as the surface application techniques. The results achieved with the prototype application system tested in this study indicates that by disturbing the soil surface prior to injection, the flow of manure to the tile drains can be reduced and thereby reduce the levels of nutrient and bacterial contaminants entering the rivers and lakes in the Great Lakes basin ecosystem.
7. TECHNOLOGY TRANSFER POTENTIAL:
The potential for transferring and disseminating the technological advancements of this study have been greatly enhanced by the collaboration of the Ontario Ministry of Agriculture Food and Rural Areas and the Upper Thames River Conservation Authority. These organizations are routinely involved in agricultural extension activities and have already proven effective in finding cooperating farmers for on-farm research activities. Their direct involvement in this research will facilitate a rapid dissemination of the study findings and an improved understanding of their implications. In addition, Husky Farm Equipment Ltd., the manufacturer of the prototype injection system, has been involved in the development of the tanker application unit and has provided ongoing support for the modification and maintenance of the applicator tanker as the project has been in progress.
The effectiveness of cultivating prior to manure injection has been demonstrated through the results of this study at the field scale. This is valuable and convincing information for the farming community so that the impacts of manure application to tile drained fields can be fully appreciated.
8. GAPS/NEEDS FOR FUTURE RESEARCH
While this study has identified the levels of nutrients and bacteria in tile drains and surface runoff which may be expected from the application of liquid manure under the study conditions to soils at a particular rate under conservation tillage systems, more work is needed to establish a system to predict environmentally safe rates of manure application to land. In addition, the significance of the levels of contamination being observed at various rates of application to the ecological health of the receiving bodies of water requires further investigation.
Further work should be directed towards determining the relevance of the findings of this study to other soil types. While this study has pointed to macropore flow as a likely pathway of manure to the tile drains, additional research is needed to more precisely determine the pathways and processes of nutrient and bacteria transport. Additional validation of predictive water quality models with field scale data would enhance their use for predicting scenarios during which water quality standards are likely to be exceeded.
Thursday, May 05, 2011 03:03:22 PM