For many agricultural commodity sectors, efforts to meet international obligations regarding emissions reduction are increasing. The Australian cotton industry has already made advances in this regard and the high yields associated with Australian cotton production dramatically minimise greenhouse gas emissions intensity. However, certainty about the quantum of greenhouse gas emissions and the relative contribution of different components of the emissions profile is somewhat unclear; and opportunities for farm-level practice change have not been fully explored. The objectives of this paper were to, (a) build a robust greenhouse gas emissions profile for the product-chain of Australian cotton fibre (lint) grown in northwest New South Wales, (b) using Life Cycle Assessment (LCA), compare the relative contributions of the different industries involved in the product-chain of cotton fibre (e.g. fertiliser producers, cotton farmers, cotton ginning plants) and (c) assess the effects of an array of on-farm mitigation options. Testing the various management options provides information for growers and policy-makers about the relative emissions reduction benefits possible. Additionally, we compared results of previous Australian cotton production studies using similar assumptions and extrapolated the emissions profile to a national scale, with the intention of informing commodity and carbon markets.
The foreground data for the study were for the three production seasons from 2011-2012 to 2013–2014 in northwest New South Wales, with a functional unit of one tonne of cotton lint at port. We also drew upon published data, survey data, scientific literature and Australian and international databases. To ensure consistency between our approach and that applied to meet international emissions reporting obligations, we applied emissions formulae and factors from the Australian National Inventory Report, except where more specific published data were available. We assumed that 96% of production was from irrigated systems, with 85% of irrigation water pumped by diesel-powered irrigation pumps and a median irrigated yield of 10.3 bales per ha. We tested the sensitivity of the resulting emissions profile to a wide array of enterprise assumptions and calculation variables.
The climate change impact of cotton lint on a cradle-to-port basis was 1601 kg CO2e per tonne of cotton lint. The ‘hot-spots’ within the emissions profile included the production and use of synthetic nitrogen (N) fertilisers (46% of emissions), the production and use of electricity and diesel used for irrigation (10%) and the production and use of diesel for farm machinery (9%).
Farm level management options with potential to minimise life cycle GHG emissions were: reducing N fertiliser rate from a commercial rate of 255 kg N/ha to 240 kg N/ha or 180 kg N/ha (2.6% and 13.2% emissions reduction); use of controlled-release and stabilised N fertilisers (5.9% reduction), changing from diesel to solar-powered irrigation pumps (8.1% reduction), changing from diesel to biofuel-powered farm machinery (3.4% reduction), changing from continuous cotton to a cotton-legume crop rotation (3.9% reduction) and use of N fertigation (2.1% reduction). Whilst we focused on farm-level mitigation strategies, these changes were placed in the context of the cradle-to-gate system, to account for associated changes in pre-farm and post-farm emissions.