Conservation agriculture reduces climate change impact of a popcorn and wheat crop rotation

Life cycle assessment (LCA) has been used in environmental assessment of agricultural products and systems for several decades. LCA is a methodological framework that estimates potential environmental impacts of a product by quantifying the resources consumed and pol- lutant emissions to the environment in the course of its life cycle [15, 16]. It allows a multi-cri- teria assessment, considering a range of environmental impacts. The carbon footprint method assesses the total amount of GHG emissions that are directly and indirectly caused by an activ- ity or are accumulated over the life stages of a product [17]. It quantifies a single criterion, the LCA climate change impact. Conservation agriculture practices have been studied using LCA, e.g. [14] compared con- ventional tillage and no tillage and [18] assessed the effect of the introduction of cover crops. Yang et al. [19] used carbon footprint methodology to assess the effect of diversification of crop rotation. Surprisingly, we found no LCA or carbon footprint studies that compared con- servation agriculture, i.e. the combination of no tillage, organic soil cover and crop rotation, to conventional agriculture. The objectives of this study were to (i) assess short-term effects of an innovative conserva- tion agriculture popcorn and wheat crop rotation on SOC sequestration, GHG emissions, and the environmental impacts climate change, terrestrial acidification, marine eutrophication, land competition and cumulative energy demand, and (ii) to quantify the potential mid- to

long-term benefits of conservation agriculture for SOC sequestration and these environmental impacts. 2. Materials and methods 2.1 Life cycle assessment Conservation agriculture differs from conventional agriculture both with respect to input use (e.g. tractors, seed for cover crops) and with respect to its sequestration of SOC. LCA allows a whole system comparison of conventional and conservation agriculture by considering simul- taneously off-farm resource use and emissions of GHG and other pollutants (associated with inputs), on-farm resource use and emissions of GHG and other pollutants (e.g. from diesel combustion) and SOC changes corresponding to CO2 emissions or sequestration. 2.1.1 Goal and scope definition. The goal of the study was to assess and compare poten- tial environmental impacts of conventional and conservation agriculture in a popcorn and wheat crop rotation using attributional LCA. The system boundaries of the crop rotations began with the extraction of resources and ended at the farm gate. Processes included the pro- duction of all inputs and all processes related to crop production: (1) soil cultivation, sowing, weed control, fertilisation, pest and pathogen control, harvest; (2) machines and the buildings or areas used to park them; (3) seeds for cash and cover crops, fertilisers including compost, pesticides, water for irrigation and fuel, as well as their transport to the farm; (4) direct emis- sions of fuel combustion, tire abrasion and pollutant emissions in the field. Post-harvest pro-

cesses, such as drying, sorting and storage were not included. The function considered was “land management”, defined as the occupation of agricultural and non-agricultural land for a given amount of time. The land occupied included both “direct” land (on-farm) and “indirect” land (off-farm, e.g. to produce seeds for sowing). The functional unit was 1 ha of land occupied for 1 year (i.e. ha.year). To assess conventional and conservation agriculture rotations we used two complementary approaches: i) a comparison based on field data (for conservation agriculture) and expert judgement (for conventional agriculture) to assess short-term effects (Table 1) and ii) model- ling three agricultural scenarios to quantify long-term outcomes (Table 2). PLOS ONE Conservation agriculture reduces climate change impact of a crop rotation PLOS ONE | https://doi.org/10.1371/journal.pone.0285586 May 23, 2023 3 / 18