Research Report 1.12
|David T. Morris Box 104, Markdale, Ontario N0C 1H0|
COESA Report No.: RES/MAN-012/98
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Progress In Addressing Identified Needs for Information
Many questions about effects on the environment from livestock manures and the nutrients they contain continue to be of prime concern within rural Ontario. Several projects undertaken within The Canada-Ontario Agriculture Green Plan addressed issues related to manure and manure nutrient management and much useful information and experience were obtained. This report was prepared to facilitate the transfer of the results of these studies to extension personnel and the farmers that they serve, to the decision makers within the various levels of government, and to some degree, to the general public.
This report provides a summary of the major observations and conclusions of eight Green Plan research reports, with particular reference to water quality and greenhouse gas issues, along with supplementary information from one project funded through the Land Management Assistance Program and four projects of the Rural Conservation Clubs Program.
The first project completed within the Green Plan Research Sub-program was the report, The Current State of the Art on Manure/Nutrient Management by Goss et al, 1994. It identified and ranked twelve priority areas for research and extension activities, related to manure nutrient management. It also included a literature review summarizing the extent of the knowledge about manure/nutrient management as of 1993 and identified the major gaps in the information base regarding the environmental impact of manure management. Throughout this current report, the report by Goss et al and recommendations made by the committees and sub-committees of the Ontario Agricultural Services Coordinating Committee (OASCC) were used as benchmarks against which to compare the progress made within Green Plan. Results from Green Plan projects are summarized according to the contributions made toward answering specific concerns identified by Goss et al or by OASCC. Unresolved concerns or gaps in the knowledge base and recommendations for future actions, as noted in the individual reports by the respective researchers, are also documented.
Progress In Addressing Identified Needs for Information
Manure use in conservation tillage systems was investigated in on-farm trials. Application of liquid manure was integrated with conservation tillage in an effective and efficient manner, from an operational point of view, although modification of application equipment was sometimes necessary depending on site requirements. If tile drains were flowing at the time of application, side-dressed applications of liquid manure in no-till corn resulted in impairment of the quality of tile drainage water such that water quality guidelines for bacteria, ammonia and phosphorus were exceeded for several hours. This occurred both immediately following the manure application (i.e. within minutes) and after a simulated rainfall event one day later, regardless of the method of liquid manure application. Manure was confirmed as the source of the contamination and macropore pathways contributed to tile flows even under unsaturated soil moisture conditions. Compared to surface application, contamination was generally less when the manure had been injected, especially if the system was modified to till the soil before injection. Guidelines were developed to help reduce contamination of tile drainage water from application of liquid manure in no-till situations.
Corn yields produced with manure-nitrogen applied at rates based on soil N test recommendations were generally equivalent to those from control treatments where inorganic fertilizers were used at equivalent rates.
The availability of manure nitrogen to a crop was most directly related to the ammoniacal nitrogen (NH4-N) content of the manure. This fraction must be measured and taken into account if manure N is to be used most economically with minimum environmental impact. The release of available N from spring-applied manures with high NH4-N contents (e.g. liquid swine and cattle manures) was rapid in some years and well in advance of the period of peak N requirement of the corn crop. Solid manures with a low content of NH4-N and a high C/N ratio (e.g solid beef cattle manure) provided little N to the crop in the year of application. They did not cause a depression in available N in the soil, contrary to expectations.
Determination of the availability of N in the soil early in the growing season was complicated by the apparent disappearance of N. Within a few days after application, the amount of inorganic nitrogen that could be extracted from the soil was always less than the amount of NH4-N applied in manures or urea. The N in liquid swine manure was generally more available than that in other manures (i.e cattle or poultry). The availability of N in solid beef cattle manure was generally the lowest. Manure N from all sources was less available than N from fertilizer urea.
Manure N dynamics in the soil, related to N mineralization and immobilization, were difficult to assess because of the differences in inorganic N recoveries and variable release rates in the soil. Similar difficulties were experienced in estimating the contribution of available N from the organic N fraction of manures. Nevertheless, there appeared to be little, if any, early-season release of organic N from spring-applied manures. Release of organic N occurred late in the growing season or in subsequent seasons. There was evidence that some of the organic N in fall-applied manure became mineralized in the late summer, twelve months after application. Significant quantities of residual manure N can become available in the year following application. Unfortunately, the soil test for nitrate nitrogen did always not accurately reflect the contribution of nitrogen from previous manure applications and other organic sources of nitrogen such as residues from legume crops or cover crops.
Manure N transformations in moderately acid soils (e.g. mineralization and nitrification) occurred at a slower rate than in neutral or slightly alkaline soils. However, soil acidity had little influence on the extent of N transformations. Liming of these acid soils resulted in an increase in the rate of mineralization and nitrification to near normal levels. Provided that such soils receive lime treatments periodically, soil acidity should not interfere with the availability of manure-N in most circumstances.
The implications for groundwater quality of using liquid manure were found to be similar to those of using mineral N sources at equivalent rates of inorganic N. There was a high risk of nitrate leaching from fall applications of liquid manures with a high NH4-N content (e.g. liquid swine or liquid dairy cattle manures). This risk existed in the fall immediately after application, in the following spring, and in the next fall period. There appeared to be little risk of water quality impairment from fall-application of composted manures, composted organic wastes or solid manures with relatively low NH4-N content and substantial bedding content, but these materials also provided little N to the corn crop in the first year.
Fall treatments, designed to immobilize nitrogen, (e.g. seeding of cover crops or adding straw) were not adequate to reduce the risk of nitrate leaching significantly. Cover crops sown after manure application in the fall removed less than 10% of mineral-N applied in liquid cattle manure, and only 10% - 15% of this was transferred to the following corn crop. Much of the N from fall-seeded cover crops did not appear to be become available until late in the following season.
Adjustments in the level and degradability of protein in the diets of dairy cattle were more likely to affect the form of the nitrogen excreted (i.e. urine vs faeces) than the total amount. Feeding a diet with high protein content and degradability to dairy cattle had little effect on the N content of the faeces, but increased excretion of nitrogen in the urine. The major source of available N in cattle manure appears to be derived from the urine. Faeces may even restrict N availability. Dietary changes that increase the proportion of N excreted in the urine could influence N utilization by crops, gaseous losses or leaching.
The fate of nitrogen inputs in six different conventional manure handling systems varied depending on the manure and the system. The amount of N excreted as fresh faeces was consistently 70 - 80% of feed N. As a percentage of N inputs (feed + bedding), final plant available manure NH4-N amounts ranged between 8% (solid beef) and 40% (liquid swine or liquid dairy). Organic N in the manure varied from 1% (liquid swine) to 45% (solid dairy) of input N. The major pathway of N loss was as ammonia (NH3) volatilization from fresh manure (22 - 65% of excreted N). Because this loss of N occurred very quickly before the manure was moved into storage, there appear to be few management options for reducing it. In comparison, losses in storage were relatively low for most systems (3 to 23% of manure N). Aerobic conditions in one storage lagoon for liquid swine manure system resulted in high concentrations of NH4-N in the liquid manure, leading to significant loss of NH3 during agitation and spreading of the manure. It is also significant to note that the nitrogen contained in runoff from a solid beef manure storage pad represented as much as 25% of the available N in the final manure to be spread.
Greenhouse gas emissions from six conventional manure handling and storage systems were monitored and an extensive database of information was collected. Greenhouse gas losses (except CO2) were usually negligible with respect to mass balance of C and N. However, the magnitudes of the losses were important from an environmental perspective. The fate of carbon inputs in conventional handling and storage systems varied depending on the manure and the system. The amount of C remaining in the final manure, as a percentage of input C, ranged between 5% (liquid swine) to 39% (liquid dairy). Losses of C in storage ranged as high as 57%.
A comparative benefit-cost assessment of six manure-handling systems, indicated that total annual costs (overhead plus operating) exceeded the value of plant nutrients applied to the soil on five of the six test farms by amounts ranging from $4.13 to $124.28 per tonne of manure applied per year. A small net benefit of $0.06/tonne manure was achieved on one dairy farm.
Soilborne diseases of potatoes can effectively be reduced through the use of manures and other related organic amendments. More than one mechanism is involved and the effects vary depending on the manure, the pathogen, soil type, and soil moisture levels. A rapid and reproducible laboratory bioassay was developed for determining the effect of manures on pathogens in a particular soil. This assay could be used to provide farmers with information as to where certain manures can be safely applied and under what conditions.
Comparison of techniques for composting manures indicated that manures from Ontario livestock operations generally do not have characteristics that minimize the loss of nitrogen or the release of methane (CH4) during composting. Solid cattle and swine manures had moisture levels significantly above the optimum of 60%. Solid poultry manures were significantly below the optimum. All manures had C/N ratios significantly below the optimum. Similarly, none of the 16 composting techniques tested showed any consistent advantage over the others for reducing losses of nitrogen or production of CH4. Because anaerobic microsites formed within the composting mass, CH4 was released during composting in all cases even though pore-space oxygen concentrations were above the 5% level considered adequate. Mixing would appear to be warranted for bacteria, enzyme and substrate distribution (as opposed to overall aeration) and should be carried out using a compost windrow turner, rather than a front-end loader, to minimize heat losses. Nitrogen losses for the sixteen composting processes studied ranged between 8.4% and 52.7%, with the average nitrogen loss being 29.7%. The benefit of a 50% reduction in manure volumes due to composting was typically offset by the value of nitrogen lost during the composting process. The use of wheat straw to optimize the C/N ratio was found to be an uneconomical strategy for reducing nitrogen losses.
Composting generally reduced the potential for leaching of nitrogen, phosphorus and potassium from the finished compost compared to the raw manure. No one process or modification was more advantageous than another in producing compost with a lower potential for leachate losses of these nutrients. The potential for leaching of nutrients from solid beef cattle manure during the composting process was low whether it was done outside or inside, because a hard crust formed on the surface of manure that effectively shed water.
Treatment systems for contaminated water were tested in three Conservation Club projects. . Results from a project to evaluate vegetated filter strips on five cattle farms established that this technology is an environmentally sound treatment system for feedlot and barnyard runoff. Sampling showed no accumulation of nutrients in the soil profile and no change in the quality of ground water samples from preconstruction levels. Two other Conservation Club projects demonstrated that constructed wetlands can be an effective means to treat milkhouse wash water and barnyard runoff without adverse effects on water quality.
Composted organic wastes can be applied at rates in the order of 100 Mg ha-1 without adverse effects on the production of corn, soybeans or grass hay. Because composts can inhibit germination of crop seeds to some degree, fall applications may be preferable to spring when higher rates of composted materials are to be applied. Relatively little of the N in these materials was in an inorganic form and it appeared that little or no N from the composts tested was made available to the crops. Thus, normal N application rates should be used in conjunction with the application of composted organic wastes. Composts did contribute significant amounts of phosphorus, potassium, and zinc to the soil, which in time, could be reflected in reduced fertilizer requirements. Three annual additions of composted organic wastes, of 10,000 to 15,000 kg carbon ha-1 yr-1, increased organic carbon levels in the soil by almost 33%, relative to where no compost was applied.
Application of composted organic wastes did not adversely affect soil quality in two soils as reflected by soluble salts, metal content or soil microbial biomass. Compost has the potential to increase water holding capacity and improve soil infiltration rates, thereby reducing risks of soil loss due to water erosion. The increased residual water content with the some composts, however, may increase the risk of delayed planting because of wet soil conditions. The impact of compost application on soil pore size distribution needs to be further investigated.
At an application rate of 100 Mg ha-1, the cost of composted urban organic wastes could not be justified on the basis of yield increases and fertilizer benefits. Indeed, these benefits were insufficient to cover the cost of the application. The intangible benefits of organic carbon, improved water characteristics, etc. might be sufficient to justify the cost of applying compost if it were delivered to the farm free of charge.
Although much useful information and experience related to manure management were gained as a result of Green Plan activities, most of the concerns identified by Goss et al or by OASCC remain to be answered more fully. In an particular, more work is needed to clarify questions related to:
Last Updated: May 16, 2011 02:33:51 PM