Research Report 1.3

 On-Farm Manure Composting Techniques:
Understanding Nitrogen and Carbon Conservation

Mr. Richard St. Jean, Ecologistics Ltd,
490 Dutton Drive, Suite A1, Waterloo, ONT N2L 6H7
COESA Report No.: RES/MAN-003/97

Objectives & Expected Outputs

Executive Summary

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Objectives and Expected Outputs
Objectives: To evaluate composting techniques suitable for use in Ontario by commercial livestock and poultry farm operations with emphasis on carbon, nitrogen and other transformations and losses, the affect on farm productivity, sustainability, environmental impact, economic viability and potential for implementation as part of an effective farm manure management and nutrient recycling program.
Expected Outputs: The technical presentation should provide information on carbon, nitrogen and other nutrient transformations and losses; the economic and physical limitation of optimizing manure carbon to nitrogen ratios; the evaporative potential of composting manure; the relative nutrient leaching potential of manures and compost; a comparison with composting techniques promoted by the Ecological Farmers of Ontario; the practicality of recycling finished compost as livestock bedding; the quantification of greenhouse gas production; and databases to establish labour, energy and capital requirements in each process.
Type: Open Bid, Industry
Spending Profile: 93-94: $132.8 K,    94-95: $114.0 K,    95-96: $62.1 K,    96-97: $91.0 K,   
Total:
$399.9 K
Status: Available February 1998

 

Executive Summary

Conventional as well as ecological on-farm manure composting techniques were studied in this project using a series of 16 composting trials. The composting trials examined carbon and nitrogen losses as well as nitrogen, phosphorus and potassium leaching losses. The effect of composting techniques on off-gas and pore-space methane (CH4), carbon dioxide (CO2), ammonia (NH3), and oxygen (O2) concentrations was also examined. Data were collected to track process temperatures, moisture losses and, in some experiments, weight changes.

Germination tests were completed using cress seed to compare seed germination inhibition levels at the end of the active composting process determined as the point at which the compost process temperature approaches ambient temperatures. Germination inhibition of the compost was also assessed after 30, 60 and 90 days of curing.

Manures were sampled from beef, dairy and poultry operations in Ontario to asses their suitability for composting in terms of moisture levels and carbon to nitrogen (C/N) ratio.

Germination Test
Germination tests to check compost maturity (lack of seed germination - inhibition)

 Manures used and composts produced as part of this project were sampled and analyzed for total nitrogen (N), phosphorus (P), potassium (K), ammoniacal nitrogen (ammonium and ammonia), nitrate (NO3) nitrogen, nitrite (NO2) nitrogen, dry matter (DM), organic matter, (OM), total carbon (TC), pH, and ash.

Solid manures produced on the dairy and beef farms sampled during this study were found to have moisture levels in the range of 70 to 80%, significantly above the optimum of 60%. Solid poultry manures were found to average 33%, significantly below the optimum. All manures had C/N ratios significantly below the optimum of 30/1 and C/N ratios ranged from 10 for poultry manures to 16 to 17 for dairy and beef.

Data collected from three different composting processes used by ecological farm operators did not indicate any advantage to these processes over conventional farm composting techniques in terms of nitrogen conservation, reduced leachate losses, or maturity as indicated by seed germination inhibition.

Comparison of traditional turned-pile, passive-aeration, and forced-aeration composting processes with similar windrow dimensions of 3 m wide by 1.2 m high, did not indicate that one process was advantageous over the other in terms of carbon or nitrogen conservation, leaching potential, or degree of seed germination inhibition.

Outside and inside composting were observed to have similar nitrogen and carbon losses and nutrient leaching potential.

The Sittler Compost Turner
A "turned-pile" composting process conducted at the Edwin Sittler Farm

The outside composting manure was observed to form a hard surface due to the sun's drying, which effectively shedded water. This hard surface reduces the potential for nitrogen leaching during the process despite the fact that it is exposed to rainfall. The net moisture loss was approximately 20% greater for the covered processes compared to the outside process. The outside process had a net moisture loss of 43.2% compared to 69.6% for the covered control process. Composting processes, manipulated for nitrogen conservation, were observed to have insufficient moisture loss to make them suitable for treatment of farm-generated liquids (e.g. barnyard runoff).

Composting manure suspended on load cells

Composting in bins suspended on load cells for weight-loss monitoring

Composting was found to reduce the potential for N, P and K leaching compared to raw manure. Fourteen out of sixteen processes studied showed a reduction in N, P and K leaching losses as a result of composting.

The study indicated that windrows 3 m wide and 1.2 m high have sufficient natural convection through them to maintain aerobic conditions without aeration enhancements such as forced-aeration, static aeration tubes or mixing. Mixing, however, was observed to stimulate bacterial activity (as indicated by a temperature increase after mixing), even when pore-space oxygen levels were not limiting. This is believed to be due to the redistribution of bacteria, enzymes, and substrate.

Mixing using a tractor loader was found to cause significantly greater heat losses during mixing than the use of a compost windrow turner for mixing. This initial heat loss was observed to reduce the rate of natural convention and create a temporary oxygen deficit, increasing the potential for CH4 production, until the temperature recovered. Based on the data collected, mixing is warranted for bacteria, enzyme and substrate distribution as opposed to aeration and should be carried out using a compost windrow turner to minimize heat losses.

Passive aeration composting

Passive aeration composting process set up for on-line monitoring of pore space and off-gas composition.

The data collected did not indicate that one composting technique was advantageous over another in reducing the production of CH4. Anaerobic microsites were found to exist regardless of the technology used. Establishment of anaerobic microsites is a function of the non-homogenous nature of manure. Forced-aeration processes without mixing were not observed to reduce CH4 concentrations in pore-spaces or off-gases. It is believed that mixing will help reduce the level of anaerobic microsites.

Compost curing for up to 90 days was observed to be insufficient time for the chemical transformations necessary to eliminate seed germination inhibition, characteristic of composts at the end of the active heating cycle of composting processes. There was no evidence from the data collected that compost curing up to 90 days would reduce the potential for nitrogen leaching.

Real-time gas monitoring system

On-Line data acquisition system with CO2/O2  analyzer and computer

The benefit of a 50% reduction in manure volumes due to composting is typically offset by the value of the nitrogen lost during the composting process. Nitrogen losses during composting for beef cattle manure were found to be equivalent in value to the reduced spreading costs. The reduced spreading costs for dairy cattle manure as a result of composting were found to yield a net benefit of $0.41/T (wet) manure composted after N losses were accounted for. In the case of poultry manure, the cost of nitrogen loss exceeds the benefit of reduced spreading costs by $5.10/T (wet).

 


 

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