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

cover crop) and 26% of soil C (cover crop + compost). Conservation agriculture resulted in soil C sequestration over several decades, until a new soil C equilibrium was reached. 1. Introduction The Intergovernmental Panel on Climate Change [1] has reiterated the need for urgent action to ensure the future of humanity under climate change. To remain within the target of no more than 1.5˚C of warming, urgent action at unprecedented scales and across all sectors is required within the next 10 years. According to IPCC [2], 24% of total greenhouse gas (GHG) emissions worldwide are caused by the agricultural sector. Consequently, agriculture has a major role in meeting the 1.5˚C target through lowering its GHG emissions and sequestering carbon dioxide (CO2) in the soil. At the same time, agricultural systems need to adapt to cli- mate change, and produce sufficient food for a growing world population, while preserving biodiversity, water and soil. Soil carbon (C) sequestration can contribute to reducing net anthropogenic GHG emis- sions, while preserving and restoring soil health by maintaining and increasing soil organic matter, thus helping to increase production resilience and food security [3]. Conservation agri- culture is based on three crop management principles: no tillage, permanent organic soil cover with crop residues and/or cover crops, and crop rotation [4]. Conservation agriculture addresses several environmental and management issues. Planting of cover crops can improve soil quality by providing a source of substrate for microbial activity,

which enhances soil C and nitrogen (N) cycles [5]. Soil erosion decreases when soils are less dis- turbed by tillage and are enriched with biomass from cover crops and organic fertilisation [6]. Cover crops also increase N-use efficiency: they take up soil N left by the previous crop, thus decreasing nitrate (NO3) leaching and providing N from cover crop residues to the next crop [7]. Finally, conservation agriculture usually has lower production costs than conventional agri- culture, due to reduced use of inputs (e.g. fuel) and less time spent in the field [8, 9]. Conservation agriculture is not common in popcorn (Zea mays) and wheat (Triticum aesti- vum) rotations in France. In current conventional popcorn and wheat rotations, the soil is ploughed in autumn, remains bare in winter, and only mineral fertiliser is applied. This type of management is prone to soil erosion and NO3 leaching, and results in low stocks of soil organic matter, which negatively influences soil structure and soil water retention [10]. The Nataïs company, Europe’s main popcorn producer, started transitioning towards conservation agriculture approximately two decades ago [11], with reduced tillage, inclusion of cover crops, and application of organic fertiliser. Several studies have highlighted the importance of soil organic C (SOC) dynamics when estimating the C footprint of agricultural systems, particularly when conservation agriculture practices are used [12, 13]. These studies have shown that planting cover crops and using

reduced or no tillage are good strategies to increase soil C content. These practices also tend to increase in-field N2O emissions, due to the incorporation of cover crop residues, and may cause additional CO2 emissions related to fuel combustion. Overall, conservation agriculture has lower net GHG emissions than conventional agriculture [13, 14] because the effect of soil sequestration on net GHG emissions is superior to that of increased N2O and CO2 emissions. Similarly, Prechsl et al. [14] found that using organic fertiliser (cattle slurry) rather than min- eral N fertiliser in a 6-year rotation with cover crops in Switzerland emitted more in-field N2O. However, the GHG emissions associated with production of mineral N fertiliser tipped the net GHG emissions in favour of organic fertilisation. 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 2 / 18 study results, but had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Abbreviations: ˚C, degree Celsius; C, carbon; Ccomp, organic C input from compost; Ccover, organic C input from cover crops; Ccrop, organic C input from cash-crop residues; Cd, cadmium; Cmin, mineralisation of soil C; CO2, carbon dioxide; CO2-eq., carbon dioxide-equivalent; Cons_CC, conservation agriculture with cover crops scenario; Cons_full, conservation agriculture with cover

crops and compost scenario; Conv, conventional agriculture scenario; Cr, chromium; Cseq, organic C input from humified C sequestered; Cu, copper; GHG, greenhouse gas; Ha, hectare; Hg, mercury; IPCC, Intergovernmental Panel on Climate Change; ISO, international organization for standardization; LCA, life cycle assessment; LCI, life cycle inventory; N, nitrogen; N2O, nitrous oxide; NH3, ammonia; Ni, nickel; NO3, nitrate; NOx, nitrogen oxides; P, phosphorous; Pb, lead; PO4, phosphate; SOC, soil organic carbon; t, ton; Zn, zinc.