Résumé
Introduction: Cotton is the most produced natural fibre in the world, with an annual output of 23 million t of lint in the period 2000–2013. Africa produced in average 6% of that output, and despite being a relatively minor contributor to global cotton supply chains, it has been estimated that a large percentage of the continent's population depends on cotton cultivation for their livelihood. Most published cotton LCAs focused on the main global producers (India, China, USA), a few consider African cotton, and none to date Malian cotton. This work presents an LCA of the Malian cotton sector, consisting of an agricultural phase and ginning operations, in contrast with other African and global cotton LCAs. Material and methods: The goal of the study is to assess the absolute and relative environmental impacts of Malian cotton, per agricultural production system type, including the processing of seed cotton in ginning plants to produce cotton fibre bales (cradle to processing plant gate). Inventories were built for the two initial phases in the production cycle of cotton fibre, namely, the agricultural phase and the ginning phase. The main agricultural production system types were identified, according to distinctive differences in yields and technical processes―such as phytosanitary strategies―as well as the main processes performed in ginning plants. Operational data, representing the period 2002–2010, were provided by the Malian Company for the Development of Textiles (CMDT). It included yields and input and their uncertainty data. Direct field emissions of the agricultural phase were estimated following the AGRIBALYSE methodology, adapted when necessary to tropical conditions (e.g. a modified version of the Indigo-N model set was used to estimate N losses). Impact assessment was based on the European-sanctioned ILCD 2011 Midpoint+ v1.0.9, May 2016 method. Sensitivity was explored with scenarios and uncertainty data was propagated with Monte Carlo. Results and discussion: The agricultural phase of cotton production in Mali differs from that of the largest producing countries, in that it is non-irrigated and non-mechanised and that non-Bt varieties are used. Instead, Malian cotton is rainfed―thus produced during the rainy season, from April/May to October/November―in rotation with maize or sorghum, manual work is prevalent up to the harvest, ploughs are towed by animals, and local varieties are grown (mainly STAM 59A and NTA 90-5). Malian yields were in the order of 400 kg lint/ha in the period 2001–2018, corresponding to ~ 1 t seed cotton/ha. The dominant production system, conventional agriculture, was sub-classified into three sub-types based on the phytosanitary strategy followed: calendar (81%), threshold control (15%) and targeted (4%). An average conventional system type was also constructed, as a production-weighted average of calendar, targeted and threshold. An existing marginal production of organic (0.5‰) cotton was also modelled. Organic cotton products (seed cotton, lint and cottonseed) feature lower impacts than conventional both per t and per ha (except for the toxicity, climate change and eutrophication impact categories), despite comparatively lower yields, due to lower input intensity. A single score–based contribution analysis confirms that, for conventional cotton, pesticide application is the main contributor to impacts, followed by mineral fertilisers. For organic cotton, the main drivers of impacts are natural pesticides and organic fertilisation. The overwhelming contribution of pesticides is largely due to the provision of organophosphorus compounds, specifically the insecticide profenofos. Moreover, the ginning phase contributed very little to the overall impacts (up to 3%). When data uncertainty is considered, the impacts per t of lint are always lower for organic cotton. Conclusions: Impacts were generally larger for conventional than from organic cotton. The main hotspots are related to pesticide use, and therefore, efforts should focus on that factor, despite pesticide inputs being already relatively lower than elsewhere. Climate change indicators for Malian cotton products were compared with literature values, having similar orders of magnitude. Malian cotton production features lower yields than the main global producers do, which is mainly due to low soil fertility and, to a lesser extent, to its dependence on rainwater. A shift towards organic cotton would be desirable only if the yield gap can be overcome.