Methane and nitrous oxide emission factors from pig manure

Methane and nitrous oxide emission factors from pork manure management systems in South Africa

Industry Sector: PORK

Research Focus Area: The Economics Of Red Meat Consumption And Production In South Africa

Research Institute: University of Pretoria

Researcher: Susarah Johanna Whitehead

Title Initials Surname Highest Qualification
Dr. C.J.L Du Toit PhD
Prof W.A Van Niekerk PhD
Dr L Stevens PhD
Prof L.J Erasmus PhD

Final Report Approved: 23 August 2018

Aims Of The Project

  • 3.1.1) To identify the “on farm” manure management systems used in intensive pork production systems on a provincial basis.
  • 3.1.2) To determine the methane emissions from manure in different intensive pork production systems.
  • 3.1.3) To determine the nitrous oxide emissions from manure in different intensive pork production systems.

Short Motivation

 Methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) from manure represent a significant greenhouse gas (GHG) emissions source from intensive livestock production systems and an important mitigation opportunity. Production of N<sub>2</sub>O during storage and treatment of animal waste can occur through a nitrification-denitrification process. The amount of emissions released from manure depends on the system and duration of waste management. An additional N<sub>2</sub>O source is created if the manure is utilized as organic fertilizer on crops and pastures. Current livestock GHG inventories are based on Intergovernmental Panel on Climate Change (IPCC) Tier 1 and 2 methodologies. Tier 3 methodologies require country specific emission factors developed through experimental data. South Africa needs to develop country specific GHG emission factors based on experimental data in order to move to a Tier 3 methodology. It is crucial that <em>in situ</em> measurements are part of future strategies to improve GHG inventories and develop mitigation measures for livestock production systems.

The purpose of this study is to determine the methane and nitrous oxide emissions from a commercial pork production system under South African conditions taking into account the effects of variation in temperature and humidity over different seasons, animal weight in different growth phases, ration composition provided in each phase, manure management system applied in the production unit and application of the manure on pasture. The hypothesis is that such accurate quantification of baseline emission figures will facilitate evaluation and effective adaptation of mitigation strategies. A comprehensive literature review will also be compiled on potential mitigation strategies.

Executive Summary

The purpose of this study is to determine the methane and nitrous oxide emissions from a commercial pork production system under South African conditions taking into account the effects of variation in temperature and humidity over different seasons, animal weight in different growth phases, ration composition provided in each phase, manure management system applied in the production unit and application of the manure on pasture. The hypothesis is that such accurate quantification of baseline emission figures will facilitate evaluation and effective adaptation of mitigation strategies. A comprehensive literature review will also be compiled on potential mitigation strategies.

Materials and Methods

The experiment was conducted at the TOPIGS grower farm in Dorsfontein and consisted of three sample collection periods. The sample collection periods were done during the different seasons which is the cold-dry season, the dry-warm season and the wet-hot season. Collections where done from each step of the manure management system found on the farm as well as from each growth phases of the pigs. The laboratory analyses were done at Nutrilab, Department of Animal and Wildlife Sciences, University of Pretoria. Soil analyses were done at NviroTek Labs and starch analyses were done at the South African Grain Laboratory NPC. The trial was approved by the Animal Ethics Committee of the University of Pretoria (EC015-15).

 Sample Procedure

In-house

The layout of the pork production unit at TOPIGS assigns individual housing to each production phase which has its own allocated ration type. Therefore, animals within a specific production phase receives the same ration type. The pigs in each house are similar in age and in weight. The weaner to finisher pigs are placed in group pens in each house. The floors are slatted in all of the units and temperature and humidity is recorded on a regular basis.

There are three different growth phases on the farm. The weaner phase has four houses, the grower phase has five houses and the finisher phase has four houses. Each house represents a replication and five fresh manure samples were taken from each replication during each sampling period. The fresh manure samples were pooled to form a composite sample and again sub-sampled into three different chambers. Gas samples were taken from each subsample and stored in 5 ml pre-evacuated vials and manure samples were taken from each sub-sample. This was done for each phase.

Each house has a slurry pit with a plug that is used to release the slurry to the central canal. A composite sample of the slurry per treatment and replicate was taken and sub-sampled for gas analysis.  A manure sample was taken at each sampling point for analysis in the laboratory. This was done for each growth phase.

Gas samples were taken at 0, 10, 20 and 30 minutes and analysed for methane, nitrous oxide and carbon dioxide using closed static chambers and GC with a FID and ECD detector. Manure samples collected from each sub-sample site was analysed for dry matter, ash, total-N, total carbon, total ammonia nitrogen, volatile solids, temperature and pH. Feed samples were also taken during each sampling period for proximal nutrient analysis in the laboratory according to standard procedures. Environmental data was collected at each sample site during the different seasons.

Lagoons

There are three lagoons located on the experimental site. The first lagoon is covered and flows into the second lagoon which flows into the third lagoon where the liquid manure is aerated. From the covered lagoon gas samples were collected from the outlets.

The open lagoons were divided into a grid of equal parts from which representative manure samples was taken. The slurry samples were homogenized and sub-sampled into 3 buckets and gas samples were taken at 0, 10, 20, and 30 minutes for gas analysis. Representative manure samples were taken from each sample point and analysed for dry matter, ash, total-N, total carbon, total ammonia nitrogen, volatile solids, temperature and pH. Gas samples and environmental data were gathered and analysed.

Pasture

Measurements of methane, nitrous oxide and carbon dioxide emissions with a closed chamber technique commenced immediately following slurry application on pasture.

The area of land was divided into four and random samples were taken in each quadrant. Samples on the pastures were taken twice a daily. Gas samples, environmental data and soil samples were taken and analysed.

Feed samples

Representative feed samples were taken at each sampling period and nutrient analysis took place in the laboratory according standard procedures.

Sampling Material

   The chambers used for the gas sampling procedures are classified as non-flow through or closed chambers. In these chambers there is no or very little replacement of air in the headspace so that the gas concentration increases over time. The increase in concentration with time is considered the actual flux from the manure or the soil. The material used in the chamber construction such as seals, tubing, septa and vents do not react with any gases or emit contaminants. The static closed chamber method was used to measure the N2O, CO2 and CH4 fluxes from the pasture, in addition to the use of an adapted static closed chamber method to measure emissions of these gases from fresh and slurry manure.

   The chamber used on the pasture and the bases are made of polyvinyl chloride (PVC) pipes with a diameter of 25 cm. The base has a height of 10cm and the chamber height is 20.8cm. The base was permanently placed in the soil and the upper part of the chamber was placed and sealed on top of the base at the time of sampling with tubing to prevent air to escape or penetrate. The installation of chambers or bases causes soil disturbance, which may impact gas emissions, therefore bases are inserted permanently in the place where measurement is to take place during the time of gas sampling. The chamber was coated with a reflective material such as aluminium sheets to minimize internal heating by solar radiation. The plastic white buckets used during the gas sampling of the fresh manure and slurry manure was made of polyethylene. The lid closes the bucket take the bucket complete airtight. The chambers contained a sampling port to sample headspace gas by inserting a needle through a rubber septum into the headspace of the chamber to make the chamber airtight.

Sampling was performed by inserting a needle with a polypropylene syringe into the chamber septa and slowly removing 8-10 ml of gas sample and transferring it to a previously evacuated 5 ml glass vial sealed with a butyl rubber septum for storage. The vials were over-pressurized by inserting 8-10 ml of gas sample into the 5 ml vial to avoid incursion of ambient air into the vials during storage. The vials were then stored in a cooling room at the University of Pretoria until analysis.

Gas Analyses

Gas samples collected and stored were analysed using a SRI 8610C Gas Chromatograph. The gas samples from the vials were injected manually into the gas chromatograph (GC) through a sample injection valve which then enters into a carrier gas which travels to a column. Once the sample is injected into the GC column, it is separated by the carrier gas and passed through detectors specific to the particular gas such as the Thermal Conductivity Detector (TCD), Elector Capture Detector (ECD) and Flame Ionization Detector (FID) for analysis of CO2, N2O and CH4 respectively.

Greenhouse gas (GHG) emissions from different pig waste management systems in a typical pork production unit in South Africa were experimentally determined over three seasons (cold and dry, warm and dry and hot and wet) between 2015 and 2016. Specific emission factors such as temperature, pH, moisture content, growth phase and manure weight at the time of analysis are taken into account. Fluxes of methane (CH4) and nitrous oxide (N2O) from manure applied on pastures, slurry lagoons, inhouse solid manure and inhouse slurry manure were measured using closed circuit chambers. During the warmer months cumulative emissions of N2O-N and CH4-C were greater than the colder months. The total N2O emissions per day on pasture during the warmest period was 258.01g N2O-N/ha/d, 0.050mg N2O-N/m2/ d from the slurry lagoons, 1.272 mg N2O-N/m2/ d from inhouse weaner solid manure, 2.169 mg N2O-N/m2/ d from inhouse grower solid manure, 0.310 mg N2O-N/m2/ d from inhouse finisher solid manure, 3.517 mg N2O-N/m3/day from inhouse weaner slurry manure, 0.448 mg N2O-N/m3/day from inhouse grower slurry manure, and 0.913 mg N2O-N/m3/day from inhouse finisher slurry manure. The total CH4 emissions per day during the warmest seasons on pasture was 178.780g CH4-C/ ha/ d, 0.220g CH4-C /m2/ d from the slurry lagoons, 0.220g CH4-C/m2/ d from inhouse weaner solid manure, 0.193g CH4-C/m2/ d from inhouse grower solid manure, 0.255g CH4-C/m2/ d from inhouse finisher solid manure, 0.495g CH4-C/m3/day from inhouse weaner slurry manure, 0.779g CH4-C/m3/day from inhouse grower slurry manure, and 2.206g CH4-C/m3/day from inhouse finisher slurry manure. To conclude the highest emissions were observed from the pasture followed by the solid manure for the nitrous oxide emissions and the slurry manure for the methane. The least amount of nitrous oxide was observed from the lagoons and methane was observed from the solid manure. From the experimental result obtained in this study the gas flux varied during the year and was higher during the warmer periods. Changes in seasonal temperatures, manure temperatures, pH, manure weight and moisture had an effect on the emission rates. The different waste management system had an influence on the emission rates.

Please contact the Primary Researcher if you need a copy of the comprehensive report of this project – Susarah Johanna Whitehead on Whitehead.sj91@gmail.com