Modelling of selected CFI offset options

Summary

The impact of four potential Carbon Farming Initiative (CFI) methodologies on total methane and nitrous oxide emissions per hectare and per unit of production was modelled, and the financial gain to the farmer estimated. The methodologies focussed on earlier finishing of livestock, increasing forage quality, increasing reproductive performance and an investigation of emissions from a beef supply chain.

The general approach used to assess the four methodologies in this project was firstly to identify a baseline scenario for each of the issues examined and then applying the most suitable modelling tools to the analysis. The ‘baseline’ scenario for each of the methodologies defined the essential details of the modelling to be conducted including location, soil and pasture types, and livestock production system including stocking rates and calving dates.

In each case, the baseline scenario was formed from existing case studies and/or regional farm benchmarking data. The CFI methodologies were then investigated as increments of changes in management to the baseline system. In this project, a modelling approach utilising a combination of daily time step biophysical systems models (eg. Grassgro and SGS Pasture model) and spreadsheet calculators based on greenhouse gas accounting approaches (eg. Farmgas) was developed to estimate the productivity and greenhouse gas (GHG) emissions from these animal production systems.

There is currently no biophysical model that can simulate both the animal management systems and greenhouses gases (methane and nitrous oxide) within the one simulation framework. GHG emissions of methane and nitrous oxide only were considered in this analysis, in line with the rules of the CFI.

In the ‘wheat-sheep’ zone at Birchip, lamb finishing systems that primarily relied on pasture had the lowest total meat sold, the highest total emissions per hectare and the highest emissions intensity of all five systems. The proportional gains of feedlotting lambs relative to the baseline, pasture finishing system were greater for emissions intensity (≈8% for feedlotting wether lambs only and ≈14% for feedlotting all lambs) than for total emissions (4-5% for all feedlotting scenarios). If the farmer was paid $20/t CO2-e, these reductions in total emissions would lead to a payment equivalent to $1.00-1.40/ha. Under the meat price and supplementary prices used in this analysis, feedlotting lambs was more profitable than the pasture finishing system, however, this result is highly sensitive to meat and supplementary feed prices and would not be profitable in all years.