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

equilibrium. When 95% of the change in SOC stock at 100 years was reached, the subsequent annual change was near zero for each scenario: -0.0005% (Conv), 0.0005% (Cons_CC), and 0.0009% (Cons_full). The Conv scenario reached this 95% threshold after 31 years, losing 9% of the initial SOC stock, whereas Cons_CC and Cons_full reached it after 34 years, gaining 14% and 26% of the initial SOC stock, respectively. After 100 years, estimated SOC stocks were 35.7 (Conv), 43.9 (Cons_CC), and 48.8 (Cons_full) t C/ha. In the south west of France approximately 7500 ha of popcorn are grown in a conventional crop rotation. Let us assume that all of this popcorn were grown in a popcorn-wheat rotation which would transition from conventional to conservation agriculture according to the Cons_CC scenario. Over a 34-year period this would allow the sequestration of 43.9–38.4 = 5.5 t/ha on 15000 ha (twice the popcorn area, because popcorn is present one year out of two in the rotation). This corresponds to an average annual C sequestration of (5.5 * 15000)/ 34 = 2426 t. The annual C footprint of a French citizen being 9 t CO2-eq. [38], this corresponds to the C footprint of 270 citizens. Initial annual climate change impacts for the scenarios were 0.19 (Cons_full), 1.64 (Cons_CC), and 4.31 (Conv) t CO2-eq./ha. As mentioned, the Cons_full scenario included a sorghum cover crop followed by a fava bean + phacelia cover crop and 6.5 t/ha of compost (Table 1). The Cons_full scenario resembled the 2017–2019 conservation system (Table 3), but

differed in that it had a single cover crop (fava bean + phacelia) and slightly different crop yields (6.8 and 6.3 t/ha for wheat and popcorn, respectively vs. 5.9 and 6.5 t/ha, respectively in the 2017–2019 system). Assuming constant management practices, the climate change impact decreased over time for Conv but increased for Cons_CC and Cons_full. Climate change Fig 3. Soil organic carbon stock (0–30 cm) over 100 years according to three scenarios of popcorn and wheat crop rotations as estimated by the SIMEOS-AMG simulation tool. See Table 2 for a description of the scenarios. https://doi.org/10.1371/journal.pone.0285586.g003 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 11 / 18