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

be equivalent to 120–460 kg CO2-eq./ha [49], smaller than the average effect of cover crops on SOC, but not insignificant. Other continued beneficial effects of cover crops include reduction of soil erosion, fixation of atmospheric N, reduction of NO3 leaching, weed suppression, and improvement of the structure of soil microbial communities [10]. 4.5 Study limitations The amount of dry matter (crop residues and compost) received by the conservation agricul- ture system was 9.6 t/ha in 2019, and 16.8 t/ha in 2020. Application of crop residues and com- post increases N2O emissions. This was taken into consideration in our estimation of N2O emissions. However, N2O emissions are particularly increased when residues are left on the soil as a mulch rather than incorporated in the soil due to inversion tillage [51, 52]. This effect was not taken into account in the modelling of N2O emissions according to the IPCC 2019 Tier 1 method we used. Consequently, we may have somewhat underestimated N2O emissions of the conservation agriculture system. The assessment of short-term effects of conservation agriculture was based on real-life farm data on yield and farming practices for the conservation rotation, while farming practices of the conventional rotation were based on expert judgement and its crop yields were assumed to be identical to those of the conservation rotation. Although the assumption regarding yield level is supported by the literature and we consider the expert judgement on farming practices

to be of high quality, the lack of field data on the reference conventional system constitutes a limitation of this study. A 10% decrease or increase of assumed conventional crop yields had a modest effect on C sequestration and climate change impact, suggesting that our results are nevertheless robust. Furthermore effects of the conservation and conventional agriculture rotations on soil car- bon dynamics are based on modelling results. This also constitutes another limitation of this study. However, an evaluation of the AMG model by comparing it to SOC results from 60 long-term field trials in France revealed that the model accurately simulated the changes in SOC stocks over time [34]. Thus, in spite of the absence of field data, we consider these model- based results to be sufficiently solid. 5. Conclusions This study revealed that implementing an innovative conservation agriculture system initially decreased the climate change impact of a popcorn and wheat rotation strongly, while moder- ately influencing marine eutrophication, terrestrial acidification, land competition, and cumu- lative energy demand. Scenario modelling revealed that a new SOC equilibrium was nearly reached after ca. 30 years, when C sequestration virtually ceased, and the climate change impact of the conservation scenarios was slightly higher than that of a conventional scenario. Modelling over 100 years revealed that at near soil C equilibrium, the SOC stock of the con- ventional scenario had decreased by 9%, whereas that of the conservation scenario had

increased by 14% and, when compost was used, by 26%. The climate change impact of the system using compost of green waste depended strongly on how impacts of the composting process were allocated between its waste treatment and compost production functions. This finding illustrates the need to establish a consensus on the allocation of composting impacts. Conservation agriculture can sequester a large amount of C until the SOC stock reaches a new equilibrium after a few decades. Shifting towards more complex systems such as agrofor- estry could enhance C sequestration further. 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 15 / 18