Odour and greenhouse gas emissions from manure spreading
Date
2010-06
Authors
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Type
Degree Level
Doctoral
Abstract
The Canadian livestock industry generates 150 million tonnes of manure annually and the majority of this manure is land applied. This practice allows the manure nutrients to be recycled to the soil crop system while improving soil fertility. However, land application of manure has the potential to negatively impact soil, water, and air quality if not managed properly. Microbial processes transform the manure nutrients into forms that are susceptible to leaching or volatilization. Balancing the nutrient loss dynamics from fertilized soil is very difficult because the nutrient transformations are affected by the soil environment such as air and water content, pH, and labile carbon content. All of these soil environmental factors can be influenced by manure application practices such as application rate, timing, and manure placement. Knowledge of how these management practices affect the soil environment can help producers make management decisions that reduce the likelihood of soil, water, and air contamination from manure application.
Very few data exist on how manure application practices affect odour emissions after spreading. Therefore, the efficiency of subsurface application in reducing odours from manure spreading for both solid and liquid manure was assessed. Flux chambers and dynamic dilution olfactometry were used to measure odour emissions from five livestock manure species applied at three application rates using surface and subsurface application methods. The results indicated that odour concentrations from injected plots were up to 66% (37% on average) lower than concentrations from broadcast applications. Injection seemed to have a larger impact on reducing odours from solid manure than liquid manure, mainly due to efficient manure coverage from solid manure injection. Odours measured immediately after solid manure applications were also 37% lower than from liquid manure applications. In general, odours from both manure types increased with higher application rates, but there was little difference in the odours among low, mid, and high application rates. The specific odour rate (odour emission rate per kg N applied) decreased with application rate due to the reduced surface area available for volatilization of compounds with higher application rates. Based on these results, injection of manure is an effective way to reduce the odour emissions immediately after spreading, particularly for solid manure. However, other factors associated with manure injection, such as the increased power requirement and soil disturbance must be considered when evaluating the overall impact of manure injection versus surface application.
The odour data collected in this study described how management practices affected odours immediately after spreading. Knowledge of how these practices affect the emission rate trend over time is required to apply dispersion models to optimize the minimum separation distances for manure spreading activities. The model parameters for an existing volatilization model were determined from field and literature data and the resulting model allowed the effects of application mode (surface vs. subsurface) and manure type (liquid vs. solid) on odour emissions for 48 hours after application to be simulated. The effects of injection depth and a coverage factor on emissions were also simulated. The modeled peak fluxes from liquid manure applications were higher than those for solid manure applications, but the extended duration of odour emissions from solid manure resulted in higher cumulative losses from solid manure applications. While the application rate had no effect on the initial odour flux, higher application rates resulted in higher peak fluxes, higher overall emissions, and longer odour durations for both manure types and application methods. Modest injection depths were shown to reduce odours from both liquid and solid manure applications compared to surface spreading. The percent reductions in cumulative odours due to injection were estimated assuming typical coverage factors. The general predictions of the model developed in this study agree reasonably well with odour emission rate trends reported in literature. Future work should focus on better estimation of the model parameters and the variation of effective diffusivity with time and soil conditions.
Greenhouse gas (GHG) emissions from agricultural activities such as land application of livestock manure cannot be ignored when assessing overall emissions from anthropogenic sources. Like odour emissions, the magnitude of the GHG emissions will be influenced by management practices such as manure placement during land application. The GHG fluxes resulting from the surface and subsurface application of liquid and solid manure were also compared within 24 hours of application using a static chamber and gas chromatography. The results showed that carbon dioxide equivalent (CO2-e) fluxes were approximately three times higher from the injected plots than the surface plots for both solid and liquid manure. The elevated CO2-e fluxes were mainly due to a pronounced increase in N2O fluxes which was likely caused by increased denitrification rates. The CO2-e fluxes from the liquid manure applications were also approximately three times higher than the CO2-e fluxes from the solid manure applications, probably due to higher levels of ammonium available for nitrification and subsequent denitrification. The CH4 fluxes were generally low and the treatments had no effect. The measured specific fluxes (total flux per kg N applied) remained relatively constant with application rate, indicating that, in this study, GHG emissions from manure applications were approximately proportional to the amount of land applied manure.
While the data from this study showed that manure type and placement influenced short-term nitrous oxide (N2O) emissions, manure management practices (particularly slurry injection or solid manure incorporation) have the potential to influence long-term emissions by changing the magnitude and pattern of the nitrogen cycle in the soil-plant system. Management practices also impact the magnitude of other nitrogen losses (ammonia volatilization, nitrate leaching) which affect indirect N2O emissions. A model that simulates the environmental conditions and nutrient transformations after manure application may allow a more reliable prediction of the effect of management practices on total GHG emissions. Numerous process-based models have been used to estimate N2O emissions as influenced by agricultural practices in Canada. However, these models do not account for enhanced denitrification that potentially exists after slurry injection or manure incorporation, resulting in an underestimation of N2O emissions. A simple mass balance of nitrogen after application to land showed that enhanced denitrification can increase total N2O-N emissions by a factor of 5. By accounting for the increased microbial activity, slower oxygen diffusion and higher water filled pore space that exists after manure injection, models may better estimate N2O emissions from manure application practices.
Description
Keywords
Liquid manure, Solid manure, Surface application, Emission rate modelling, Application rate, Injection
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Agricultural and Bioresource Engineering
Program
Agricultural and Bioresource Engineering